<?xml version="1.0" encoding="us-ascii" standalone="yes"?>
<!--XBRL Document Created with XBRLMaster-->
<!--Version: 2.3.08-->
<!--Based on XBRL 2.1-->
<!--Date of creation: 05/13/2024-->
<!--Software architectural design and coding: A'c Dharmapremananda Avt.-->
<!--Copyright (c) 2024 I-NET Business Solutions, Inc. All Rights Reserved.-->
<link:linkbase xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:roleRef roleURI="http://ptn.com/role/Cover" xlink:href="ptn-20240331.xsd#Cover" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/ConsolidatedBalanceSheets" xlink:href="ptn-20240331.xsd#ConsolidatedBalanceSheets" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/ConsolidatedBalanceSheetsParenthetical" xlink:href="ptn-20240331.xsd#ConsolidatedBalanceSheetsParenthetical" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/ConsolidatedStatementsOfOperationsUnaudited" xlink:href="ptn-20240331.xsd#ConsolidatedStatementsOfOperationsUnaudited" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/ConsolidatedStatementsOfChangesInRedeemableConvertiblePreferredStockAndStockholdersDeficiencyEquityUnaudited" xlink:href="ptn-20240331.xsd#ConsolidatedStatementsOfChangesInRedeemableConvertiblePreferredStockAndStockholdersDeficiencyEquityUnaudited" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/ConsolidatedStatementsOfCashFlowsUnaudited" xlink:href="ptn-20240331.xsd#ConsolidatedStatementsOfCashFlowsUnaudited" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/ORGANIZATION" xlink:href="ptn-20240331.xsd#ORGANIZATION" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/BasisOfPresentation" xlink:href="ptn-20240331.xsd#BasisOfPresentation" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/SummaryOfSignificantAccountingPolicies" xlink:href="ptn-20240331.xsd#SummaryOfSignificantAccountingPolicies" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/NewAndRecentlyAdoptedAccountingPronouncements" xlink:href="ptn-20240331.xsd#NewAndRecentlyAdoptedAccountingPronouncements" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/AssetPurchaseAgreement" xlink:href="ptn-20240331.xsd#AssetPurchaseAgreement" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/ManufacturingSupplyAgreementsForVyleesi" xlink:href="ptn-20240331.xsd#ManufacturingSupplyAgreementsForVyleesi" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/AgreementWithFosun" xlink:href="ptn-20240331.xsd#AgreementWithFosun" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/AgreementWithKwangdong" xlink:href="ptn-20240331.xsd#AgreementWithKwangdong" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/PrepaidExpensesAndOtherCurrentAssets" xlink:href="ptn-20240331.xsd#PrepaidExpensesAndOtherCurrentAssets" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/FairValueMeasurements" xlink:href="ptn-20240331.xsd#FairValueMeasurements" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/INVENTORIES" xlink:href="ptn-20240331.xsd#INVENTORIES" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/AccruedExpenses" xlink:href="ptn-20240331.xsd#AccruedExpenses" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/CommitmentsAndContingencies" xlink:href="ptn-20240331.xsd#CommitmentsAndContingencies" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/RedeemableConvertiblePreferredStockEscrowedProceedsAndStockholdersEquity" xlink:href="ptn-20240331.xsd#RedeemableConvertiblePreferredStockEscrowedProceedsAndStockholdersEquity" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/IncomeTaxes" xlink:href="ptn-20240331.xsd#IncomeTaxes" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/SummaryOfSignificantAccountingPoliciesPolicies" xlink:href="ptn-20240331.xsd#SummaryOfSignificantAccountingPoliciesPolicies" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/SummaryOfSignificantAccountingPoliciesTables" xlink:href="ptn-20240331.xsd#SummaryOfSignificantAccountingPoliciesTables" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/PrepaidExpensesAndOtherCurrentAssetsTables" xlink:href="ptn-20240331.xsd#PrepaidExpensesAndOtherCurrentAssetsTables" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/FairValueMeasurementsTables" xlink:href="ptn-20240331.xsd#FairValueMeasurementsTables" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/InventoriesTables" xlink:href="ptn-20240331.xsd#InventoriesTables" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/AccruedExpensesTables" xlink:href="ptn-20240331.xsd#AccruedExpensesTables" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/CommitmentsAndContingenciesTables" xlink:href="ptn-20240331.xsd#CommitmentsAndContingenciesTables" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/RedeemableConvertiblePreferredStockEscrowedProceedsAndStockholdersDeficiencyEquityTables" xlink:href="ptn-20240331.xsd#RedeemableConvertiblePreferredStockEscrowedProceedsAndStockholdersDeficiencyEquityTables" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/OrganizationDetailsNarrative" xlink:href="ptn-20240331.xsd#OrganizationDetailsNarrative" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/SummaryOfSignificantAccountingPoliciesDetails" xlink:href="ptn-20240331.xsd#SummaryOfSignificantAccountingPoliciesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/SummaryOfSignificantAccountingPoliciesDetailsNarrative" xlink:href="ptn-20240331.xsd#SummaryOfSignificantAccountingPoliciesDetailsNarrative" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/AssetPurchaseAgreementDetailsNarrative" xlink:href="ptn-20240331.xsd#AssetPurchaseAgreementDetailsNarrative" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/ManufacturingSupplyAgreementsForVyleesiDetailsNarrative" xlink:href="ptn-20240331.xsd#ManufacturingSupplyAgreementsForVyleesiDetailsNarrative" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/AgreementWithFosunDetailsNarrative" xlink:href="ptn-20240331.xsd#AgreementWithFosunDetailsNarrative" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/AgreementWithKwangdongDetailsNarrative" xlink:href="ptn-20240331.xsd#AgreementWithKwangdongDetailsNarrative" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/PrepaidExpensesAndOtherCurrentAssetsDetails" xlink:href="ptn-20240331.xsd#PrepaidExpensesAndOtherCurrentAssetsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/FairValueMeasurementsDetails" xlink:href="ptn-20240331.xsd#FairValueMeasurementsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/InventoriesDetails" xlink:href="ptn-20240331.xsd#InventoriesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/AccruedExpensesDetails" xlink:href="ptn-20240331.xsd#AccruedExpensesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/CommitmentsAndContingenciesDetails" xlink:href="ptn-20240331.xsd#CommitmentsAndContingenciesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/CommitmentsAndContingenciesDetailsNarrative" xlink:href="ptn-20240331.xsd#CommitmentsAndContingenciesDetailsNarrative" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/RedeemableConvertiblePreferredStockEscrowedProceedsAndStockholdersDeficiencyEquityDetails" xlink:href="ptn-20240331.xsd#RedeemableConvertiblePreferredStockEscrowedProceedsAndStockholdersDeficiencyEquityDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/RedeemableConvertiblePreferredStockEscrowedProceedsAndStockholdersEquityDetails1" xlink:href="ptn-20240331.xsd#RedeemableConvertiblePreferredStockEscrowedProceedsAndStockholdersEquityDetails1" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/RedeemableConvertiblePreferredStockEscrowedProceedsAndStockholdersEquityDetails2" xlink:href="ptn-20240331.xsd#RedeemableConvertiblePreferredStockEscrowedProceedsAndStockholdersEquityDetails2" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/RedeemableConvertiblePreferredStockEscrowedProceedsAndStockholdersEquityDetails3" xlink:href="ptn-20240331.xsd#RedeemableConvertiblePreferredStockEscrowedProceedsAndStockholdersEquityDetails3" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/RedeemableConvertiblePreferredStockEscrowedProceedsAndStockholdersEquityDetails4" xlink:href="ptn-20240331.xsd#RedeemableConvertiblePreferredStockEscrowedProceedsAndStockholdersEquityDetails4" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/RedeemableConvertiblePreferredStockEscrowedProceedsAndStockholdersEquityDetailsNarrative" xlink:href="ptn-20240331.xsd#RedeemableConvertiblePreferredStockEscrowedProceedsAndStockholdersEquityDetailsNarrative" xlink:type="simple" />
  <link:roleRef roleURI="http://ptn.com/role/IncomeTaxesDetailsNarrative" xlink:href="ptn-20240331.xsd#IncomeTaxesDetailsNarrative" xlink:type="simple" />
  <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" />
  <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" />
  <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" />
  <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" arcroleURI="http://xbrl.org/int/dim/arcrole/all" />
  <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#notAll" arcroleURI="http://xbrl.org/int/dim/arcrole/notAll" />
  <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/Cover" xlink:title="00000001 - Document - Cover Page Information">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_CoverAbstract" xlink:label="loc_deiCover" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/ConsolidatedBalanceSheets" xlink:title="000002 - Statement - Consolidated Balance Sheets">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaapStatementLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaapStatementTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStatementTable" order="2000" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaapStatementClassOfStockAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapStatementClassOfStockAxis" order="20" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaapClassOfStockDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapStatementClassOfStockAxis" xlink:to="loc_us-gaapClassOfStockDomain" order="30" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaapClassOfStockDomain_10" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaapStatementClassOfStockAxis" xlink:to="loc_us-gaapClassOfStockDomain_10" order="40" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_SeriesAConvertiblePreferredStocksMember" xlink:label="loc_ptnSeriesAConvertiblePreferredStocksMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapClassOfStockDomain" xlink:to="loc_ptnSeriesAConvertiblePreferredStocksMember" order="21" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:label="loc_us-gaapCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MarketableSecuritiesCurrent" xlink:label="loc_us-gaapMarketableSecuritiesCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapMarketableSecuritiesCurrent" order="2" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccountsReceivableNetCurrent" xlink:label="loc_us-gaapAccountsReceivableNetCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapAccountsReceivableNetCurrent" order="3" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InventoryNet" xlink:label="loc_us-gaapInventoryNet" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapInventoryNet" order="4" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:label="loc_us-gaapPrepaidExpenseAndOtherAssetsCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapPrepaidExpenseAndOtherAssetsCurrent" order="5" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetsCurrent" xlink:label="loc_us-gaapAssetsCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapAssetsCurrent" order="6" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="loc_us-gaapPropertyPlantAndEquipmentNet" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapPropertyPlantAndEquipmentNet" order="7" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingLeaseRightOfUseAsset" xlink:label="loc_us-gaapOperatingLeaseRightOfUseAsset" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapOperatingLeaseRightOfUseAsset" order="8" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherAssetsNoncurrent" xlink:label="loc_us-gaapOtherAssetsNoncurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapOtherAssetsNoncurrent" order="9" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Assets" xlink:label="loc_us-gaapAssets" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapAssets" order="10" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccountsPayableCurrent" xlink:label="loc_us-gaapAccountsPayableCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapAccountsPayableCurrent" order="11" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccruedLiabilitiesCurrent" xlink:label="loc_us-gaapAccruedLiabilitiesCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapAccruedLiabilitiesCurrent" order="12" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingLeaseLiabilityCurrent" xlink:label="loc_us-gaapOperatingLeaseLiabilityCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapOperatingLeaseLiabilityCurrent" order="13" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FinanceLeaseLiabilityCurrent" xlink:label="loc_us-gaapFinanceLeaseLiabilityCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapFinanceLeaseLiabilityCurrent" order="14" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherLiabilitiesCurrent" xlink:label="loc_us-gaapOtherLiabilitiesCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapOtherLiabilitiesCurrent" order="15" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LiabilitiesCurrent" xlink:label="loc_us-gaapLiabilitiesCurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapLiabilitiesCurrent" order="16" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent" xlink:label="loc_us-gaapOperatingLeaseLiabilityNoncurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapOperatingLeaseLiabilityNoncurrent" order="17" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FinanceLeaseLiabilityNoncurrent" xlink:label="loc_us-gaapFinanceLeaseLiabilityNoncurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapFinanceLeaseLiabilityNoncurrent" order="18" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherLongTermDebt" xlink:label="loc_us-gaapOtherLongTermDebt" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapOtherLongTermDebt" order="19" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherLiabilitiesNoncurrent" xlink:label="loc_us-gaapOtherLiabilitiesNoncurrent" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapOtherLiabilitiesNoncurrent" order="20" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Liabilities" xlink:label="loc_us-gaapLiabilities" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapLiabilities" order="21" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommitmentsAndContingenciesDisclosureAbstract" xlink:label="loc_us-gaapCommitmentsAndContingenciesDisclosureAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapCommitmentsAndContingenciesDisclosureAbstract" order="22" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_ContingentlyRedeemableWarrants" xlink:label="loc_ptnContingentlyRedeemableWarrants" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnContingentlyRedeemableWarrants" order="23" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:label="loc_us-gaapLiabilitiesAndStockholdersEquityAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapLiabilitiesAndStockholdersEquityAbstract" order="24" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_PreferredStockAbstract" xlink:label="loc_ptnPreferredStockAbstract" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnPreferredStockAbstract" order="25" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PreferredStockValue" xlink:label="loc_us-gaapPreferredStockValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapPreferredStockValue" order="26" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockValue" xlink:label="loc_us-gaapCommonStockValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapCommonStockValue" order="27" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdditionalPaidInCapital" xlink:label="loc_us-gaapAdditionalPaidInCapital" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapAdditionalPaidInCapital" order="28" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="loc_us-gaapRetainedEarningsAccumulatedDeficit" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapRetainedEarningsAccumulatedDeficit" order="29" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquity" xlink:label="loc_us-gaapStockholdersEquity" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStockholdersEquity" order="30" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="loc_us-gaapLiabilitiesAndStockholdersEquity" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapLiabilitiesAndStockholdersEquity" order="31" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/ConsolidatedBalanceSheetsParenthetical" xlink:title="000003 - Statement - Consolidated Balance Sheets (Parenthetical)">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaapStatementLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaapStatementTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStatementTable" order="2000" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaapStatementClassOfStockAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapStatementClassOfStockAxis" order="10" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaapClassOfStockDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapStatementClassOfStockAxis" xlink:to="loc_us-gaapClassOfStockDomain" order="20" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaapClassOfStockDomain_10" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaapStatementClassOfStockAxis" xlink:to="loc_us-gaapClassOfStockDomain_10" order="30" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_SeriesAConvertiblePreferredStocksMember" xlink:label="loc_ptnSeriesAConvertiblePreferredStocksMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapClassOfStockDomain" xlink:to="loc_ptnSeriesAConvertiblePreferredStocksMember" order="11" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PreferredStockParOrStatedValuePerShare" xlink:label="loc_us-gaapPreferredStockParOrStatedValuePerShare" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapPreferredStockParOrStatedValuePerShare" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PreferredStockSharesAuthorized" xlink:label="loc_us-gaapPreferredStockSharesAuthorized" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapPreferredStockSharesAuthorized" order="2" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="loc_us-gaapCommonStockParOrStatedValuePerShare" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapCommonStockParOrStatedValuePerShare" order="3" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="loc_us-gaapCommonStockSharesAuthorized" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapCommonStockSharesAuthorized" order="4" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockSharesIssued" xlink:label="loc_us-gaapCommonStockSharesIssued" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapCommonStockSharesIssued" order="5" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="loc_us-gaapCommonStockSharesOutstanding" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapCommonStockSharesOutstanding" order="6" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PreferredStockSharesIssued" xlink:label="loc_us-gaapPreferredStockSharesIssued" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapPreferredStockSharesIssued" order="7" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PreferredStockSharesOutstanding" xlink:label="loc_us-gaapPreferredStockSharesOutstanding" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapPreferredStockSharesOutstanding" order="8" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/ConsolidatedStatementsOfOperationsUnaudited" xlink:title="000004 - Statement - Consolidated Statements of Operations (unaudited)" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/ConsolidatedStatementsOfChangesInRedeemableConvertiblePreferredStockAndStockholdersDeficiencyEquityUnaudited" xlink:title="000005 - Statement - Consolidated Statements of Changes in Redeemable Convertible Preferred Stock and Stockholders (Deficiency) Equity (unaudited)">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaapStatementLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaapStatementTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStatementTable" order="2000" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaapStatementEquityComponentsAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapStatementEquityComponentsAxis" order="20" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaapEquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapStatementEquityComponentsAxis" xlink:to="loc_us-gaapEquityComponentDomain" order="30" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaapEquityComponentDomain_10" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaapStatementEquityComponentsAxis" xlink:to="loc_us-gaapEquityComponentDomain_10" order="40" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_SeriesAConvertiblePreferredStockMember" xlink:label="loc_ptnSeriesAConvertiblePreferredStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEquityComponentDomain" xlink:to="loc_ptnSeriesAConvertiblePreferredStockMember" order="21" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaapCommonStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEquityComponentDomain" xlink:to="loc_us-gaapCommonStockMember" order="22" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_ContigentlyRdeemableWarrantMember" xlink:label="loc_ptnContigentlyRdeemableWarrantMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEquityComponentDomain" xlink:to="loc_ptnContigentlyRdeemableWarrantMember" order="23" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:label="loc_us-gaapAdditionalPaidInCapitalMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEquityComponentDomain" xlink:to="loc_us-gaapAdditionalPaidInCapitalMember" order="24" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RetainedEarningsMember" xlink:label="loc_us-gaapRetainedEarningsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEquityComponentDomain" xlink:to="loc_us-gaapRetainedEarningsMember" order="25" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_RedeemableConvertiblePreferredStockSeriesBMember" xlink:label="loc_ptnRedeemableConvertiblePreferredStockSeriesBMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEquityComponentDomain" xlink:to="loc_ptnRedeemableConvertiblePreferredStockSeriesBMember" order="26" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_RedeemableConvertiblePreferredStockSeriesCMember" xlink:label="loc_ptnRedeemableConvertiblePreferredStockSeriesCMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEquityComponentDomain" xlink:to="loc_ptnRedeemableConvertiblePreferredStockSeriesCMember" order="27" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_EscrowProceedsMember" xlink:label="loc_ptnEscrowProceedsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEquityComponentDomain" xlink:to="loc_ptnEscrowProceedsMember" order="28" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharesIssued" xlink:label="loc_us-gaapSharesIssued" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapSharesIssued" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquity" xlink:label="loc_us-gaapStockholdersEquity" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStockholdersEquity" order="2" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_CumulativeEffectOfAccountingChange" xlink:label="loc_ptnCumulativeEffectOfAccountingChange" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnCumulativeEffectOfAccountingChange" order="3" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_StockBasedCompensationShares" xlink:label="loc_ptnStockBasedCompensationShares" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnStockBasedCompensationShares" order="4" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_StockBasedCompensationAmount" xlink:label="loc_ptnStockBasedCompensationAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnStockBasedCompensationAmount" order="5" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_WithholdingTaxesRelatedToRestrictedStockUnitsShares" xlink:label="loc_ptnWithholdingTaxesRelatedToRestrictedStockUnitsShares" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnWithholdingTaxesRelatedToRestrictedStockUnitsShares" order="6" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_WithholdingTaxesRelatedToRestrictedStockUnitsAmount" xlink:label="loc_ptnWithholdingTaxesRelatedToRestrictedStockUnitsAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnWithholdingTaxesRelatedToRestrictedStockUnitsAmount" order="7" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_RedemptionOfConvertibleSeriesBSeriesCPreferredStockShares" xlink:label="loc_ptnRedemptionOfConvertibleSeriesBSeriesCPreferredStockShares" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnRedemptionOfConvertibleSeriesBSeriesCPreferredStockShares" order="8" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_RedemptionOfConvertibleSeriesBSeriesCPreferredStockAmount" xlink:label="loc_ptnRedemptionOfConvertibleSeriesBSeriesCPreferredStockAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnRedemptionOfConvertibleSeriesBSeriesCPreferredStockAmount" order="9" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_SaleOfCommonStockAndWarrantsNetOfCostsShares" xlink:label="loc_ptnSaleOfCommonStockAndWarrantsNetOfCostsShares" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnSaleOfCommonStockAndWarrantsNetOfCostsShares" order="10" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_SaleOfCommonStockAndWarrantsNetOfCostsAmount" xlink:label="loc_ptnSaleOfCommonStockAndWarrantsNetOfCostsAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnSaleOfCommonStockAndWarrantsNetOfCostsAmount" order="11" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_ConversionOfLiabilityClassifiedWarrants" xlink:label="loc_ptnConversionOfLiabilityClassifiedWarrants" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnConversionOfLiabilityClassifiedWarrants" order="12" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_WarrantExcercisesShares" xlink:label="loc_ptnWarrantExcercisesShares" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnWarrantExcercisesShares" order="13" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_WarrantExcercisesAmount" xlink:label="loc_ptnWarrantExcercisesAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnWarrantExcercisesAmount" order="14" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_ReverseStockSplitFractionalSharesShares" xlink:label="loc_ptnReverseStockSplitFractionalSharesShares" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnReverseStockSplitFractionalSharesShares" order="15" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_ReverseStockSplitFractionalSharesAmount" xlink:label="loc_ptnReverseStockSplitFractionalSharesAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnReverseStockSplitFractionalSharesAmount" order="16" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_ReclassificationOfContingentlyRedeemableWarrants" xlink:label="loc_ptnReclassificationOfContingentlyRedeemableWarrants" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnReclassificationOfContingentlyRedeemableWarrants" order="17" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaapNetIncomeLoss" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapNetIncomeLoss" order="18" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_RedemptionOfConvertibleSeriesBSeriesCPreferredStock" xlink:label="loc_ptnRedemptionOfConvertibleSeriesBSeriesCPreferredStock" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnRedemptionOfConvertibleSeriesBSeriesCPreferredStock" order="19" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_WarrantExercisesShares" xlink:label="loc_ptnWarrantExercisesShares" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnWarrantExercisesShares" order="20" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_WarrantExercisesAmount" xlink:label="loc_ptnWarrantExercisesAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnWarrantExercisesAmount" order="21" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_SaleOfCommonStockAndWarrantsNetOfCosts" xlink:label="loc_ptnSaleOfCommonStockAndWarrantsNetOfCosts" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnSaleOfCommonStockAndWarrantsNetOfCosts" order="22" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_SaleOfCommonStockNetOfCostsShares" xlink:label="loc_ptnSaleOfCommonStockNetOfCostsShares" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnSaleOfCommonStockNetOfCostsShares" order="23" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_SaleOfCommonStockNetOfCostsAmount" xlink:label="loc_ptnSaleOfCommonStockNetOfCostsAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnSaleOfCommonStockNetOfCostsAmount" order="24" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_ConversionOfLiabilityClassifiedWarrantsUponWarrantExerciseShares" xlink:label="loc_ptnConversionOfLiabilityClassifiedWarrantsUponWarrantExerciseShares" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnConversionOfLiabilityClassifiedWarrantsUponWarrantExerciseShares" order="25" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_ConversionOfLiabilityClassifiedWarrantsUponWarrantExerciseAmount" xlink:label="loc_ptnConversionOfLiabilityClassifiedWarrantsUponWarrantExerciseAmount" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnConversionOfLiabilityClassifiedWarrantsUponWarrantExerciseAmount" order="26" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/ConsolidatedStatementsOfCashFlowsUnaudited" xlink:title="000006 - Statement - Consolidated Statements of Cash Flows (unaudited)" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/ORGANIZATION" xlink:title="000007 - Disclosure - ORGANIZATION" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/BasisOfPresentation" xlink:title="000008 - Disclosure - BASIS OF PRESENTATION" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/SummaryOfSignificantAccountingPolicies" xlink:title="000009 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/NewAndRecentlyAdoptedAccountingPronouncements" xlink:title="000010 - Disclosure - New and recently Adopted Accounting Pronouncements" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/AssetPurchaseAgreement" xlink:title="000011 - Disclosure - ASSET PURCHASE AGREEMENT" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/ManufacturingSupplyAgreementsForVyleesi" xlink:title="000012 - Disclosure - MANUFACTURING SUPPLY AGREEMENTS FOR VYLEESI" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/AgreementWithFosun" xlink:title="000013 - Disclosure - AGREEMENT WITH FOSUN" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/AgreementWithKwangdong" xlink:title="000014 - Disclosure - AGREEMENT WITH KWANGDONG" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/PrepaidExpensesAndOtherCurrentAssets" xlink:title="000015 - Disclosure - PREPAID EXPENSES AND OTHER CURRENT ASSETS" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/FairValueMeasurements" xlink:title="000016 - Disclosure - FAIR VALUE MEASUREMENTS" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/INVENTORIES" xlink:title="000017 - Disclosure - INVENTORIES" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/AccruedExpenses" xlink:title="000018 - Disclosure - ACCRUED EXPENSES" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/CommitmentsAndContingencies" xlink:title="000019 - Disclosure - COMMITMENTS AND CONTINGENCIES" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/RedeemableConvertiblePreferredStockEscrowedProceedsAndStockholdersEquity" xlink:title="000020 - Disclosure - REDEEMABLE CONVERTIBLE PREFERRED STOCK ESCROWED PROCEEDS AND STOCKHOLDERS EQUITY" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/IncomeTaxes" xlink:title="000021 - Disclosure - INCOME TAXES" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/SummaryOfSignificantAccountingPoliciesPolicies" xlink:title="000022 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/SummaryOfSignificantAccountingPoliciesTables" xlink:title="000023 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/PrepaidExpensesAndOtherCurrentAssetsTables" xlink:title="000024 - Disclosure - PREPAID EXPENSES AND OTHER CURRENT ASSETS (Tables)" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/FairValueMeasurementsTables" xlink:title="000025 - Disclosure - FAIR VALUE MEASUREMENTS (Tables)" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/InventoriesTables" xlink:title="000026 - Disclosure - INVENTORIES (Tables)" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/AccruedExpensesTables" xlink:title="000027 - Disclosure - ACCRUED EXPENSES (Tables)" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/CommitmentsAndContingenciesTables" xlink:title="000028 - Disclosure - COMMITMENTS AND CONTINGENCIES (Tables)" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/RedeemableConvertiblePreferredStockEscrowedProceedsAndStockholdersDeficiencyEquityTables" xlink:title="000029 - Disclosure - REDEEMABLE CONVERTIBLE PREFERRED STOCK ESCROWED PROCEEDS AND STOCKHOLDERS (DEFICIENCY) EQUITY (Tables)" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/OrganizationDetailsNarrative" xlink:title="000030 - Disclosure - ORGANIZATION (Details Narrative)" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/SummaryOfSignificantAccountingPoliciesDetails" xlink:title="000031 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details)">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaapStatementLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaapStatementTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStatementTable" order="2000" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductOrServiceAxis" xlink:label="loc_srtProductOrServiceAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_srtProductOrServiceAxis" order="20" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain" xlink:label="loc_srtProductsAndServicesDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtProductOrServiceAxis" xlink:to="loc_srtProductsAndServicesDomain" order="30" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain" xlink:label="loc_srtProductsAndServicesDomain_10" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srtProductOrServiceAxis" xlink:to="loc_srtProductsAndServicesDomain_10" order="40" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProductMember" xlink:label="loc_us-gaapProductMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtProductsAndServicesDomain" xlink:to="loc_us-gaapProductMember" order="21" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_RevenuesGross" xlink:label="loc_ptnRevenuesGross" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnRevenuesGross" order="1" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_ProductSalesAllowancesAndAccruals" xlink:label="loc_ptnProductSalesAllowancesAndAccruals" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnProductSalesAllowancesAndAccruals" order="2" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaapNetIncomeLoss" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapNetIncomeLoss" order="3" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/SummaryOfSignificantAccountingPoliciesDetailsNarrative" xlink:title="000032 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details Narrative)" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/AssetPurchaseAgreementDetailsNarrative" xlink:title="000033 - Disclosure - ASSET PURCHASE AGREEMENT (Details Narrative)" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/ManufacturingSupplyAgreementsForVyleesiDetailsNarrative" xlink:title="000034 - Disclosure - MANUFACTURING SUPPLY AGREEMENTS FOR VYLEESI (Details Narrative)" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/AgreementWithFosunDetailsNarrative" xlink:title="000035 - Disclosure - AGREEMENT WITH FOSUN (Details Narrative)" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/AgreementWithKwangdongDetailsNarrative" xlink:title="000036 - Disclosure - AGREEMENT WITH KWANGDONG (Details Narrative)" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/PrepaidExpensesAndOtherCurrentAssetsDetails" xlink:title="000037 - Disclosure - PREPAID EXPENSES AND OTHER CURRENT ASSETS (Details)" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/FairValueMeasurementsDetails" xlink:title="000038 - Disclosure - FAIR VALUE MEASUREMENTS (Details)">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaapStatementLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaapStatementTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStatementTable" order="2000" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="loc_us-gaapFairValueByFairValueHierarchyLevelAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapFairValueByFairValueHierarchyLevelAxis" order="20" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaapFairValueMeasurementsFairValueHierarchyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapFairValueByFairValueHierarchyLevelAxis" xlink:to="loc_us-gaapFairValueMeasurementsFairValueHierarchyDomain" order="30" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaapFairValueMeasurementsFairValueHierarchyDomain_10" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaapFairValueByFairValueHierarchyLevelAxis" xlink:to="loc_us-gaapFairValueMeasurementsFairValueHierarchyDomain_10" order="40" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="loc_us-gaapFairValueInputsLevel1Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFairValueMeasurementsFairValueHierarchyDomain" xlink:to="loc_us-gaapFairValueInputsLevel1Member" order="21" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="loc_us-gaapFairValueInputsLevel2Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFairValueMeasurementsFairValueHierarchyDomain" xlink:to="loc_us-gaapFairValueInputsLevel2Member" order="22" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="loc_us-gaapFairValueInputsLevel3Member" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFairValueMeasurementsFairValueHierarchyDomain" xlink:to="loc_us-gaapFairValueInputsLevel3Member" order="23" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MoneyMarketFundsAtCarryingValue" xlink:label="loc_us-gaapMoneyMarketFundsAtCarryingValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapMoneyMarketFundsAtCarryingValue" order="1" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_CashEquivalentsTreasuryBillAtCarryingValue" xlink:label="loc_ptnCashEquivalentsTreasuryBillAtCarryingValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnCashEquivalentsTreasuryBillAtCarryingValue" order="2" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_MarketableSecuritiesTreasuryBillAtCarryingValue" xlink:label="loc_ptnMarketableSecuritiesTreasuryBillAtCarryingValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnMarketableSecuritiesTreasuryBillAtCarryingValue" order="3" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_CarryingValueDuringTheYear" xlink:label="loc_ptnCarryingValueDuringTheYear" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnCarryingValueDuringTheYear" order="4" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/InventoriesDetails" xlink:title="000039 - Disclosure - INVENTORIES (Details)" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/AccruedExpensesDetails" xlink:title="000040 - Disclosure - ACCRUED EXPENSES (Details)" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/CommitmentsAndContingenciesDetails" xlink:title="000041 - Disclosure - COMMITMENTS AND CONTINGENCIES (Details)">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaapStatementLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaapStatementTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStatementTable" order="2000" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameAxis" xlink:label="loc_us-gaapPlanNameAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapPlanNameAxis" order="20" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaapPlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapPlanNameAxis" xlink:to="loc_us-gaapPlanNameDomain" order="30" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaapPlanNameDomain_10" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaapPlanNameAxis" xlink:to="loc_us-gaapPlanNameDomain_10" order="40" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_CurrentMember" xlink:label="loc_ptnCurrentMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPlanNameDomain" xlink:to="loc_ptnCurrentMember" order="21" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_OneToThreeYearsMember" xlink:label="loc_ptnOneToThreeYearsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPlanNameDomain" xlink:to="loc_ptnOneToThreeYearsMember" order="22" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_FourToFiveYearsMember" xlink:label="loc_ptnFourToFiveYearsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPlanNameDomain" xlink:to="loc_ptnFourToFiveYearsMember" order="23" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdvancesOnInventoryPurchases" xlink:label="loc_us-gaapAdvancesOnInventoryPurchases" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapAdvancesOnInventoryPurchases" order="1" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/CommitmentsAndContingenciesDetailsNarrative" xlink:title="000042 - Disclosure - COMMITMENTS AND CONTINGENCIES (Details Narrative)" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/RedeemableConvertiblePreferredStockEscrowedProceedsAndStockholdersDeficiencyEquityDetails" xlink:title="000043 - Disclosure - REDEEMABLE CONVERTIBLE PREFERRED STOCK ESCROWED PROCEEDS AND STOCKHOLDERS (DEFICIENCY) EQUITY (Details)">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaapStatementLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaapStatementTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStatementTable" order="2000" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameAxis" xlink:label="loc_us-gaapPlanNameAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapPlanNameAxis" order="10" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaapPlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapPlanNameAxis" xlink:to="loc_us-gaapPlanNameDomain" order="20" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaapPlanNameDomain_10" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaapPlanNameAxis" xlink:to="loc_us-gaapPlanNameDomain_10" order="30" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_CumulativeFromInceptionMember" xlink:label="loc_ptnCumulativeFromInceptionMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPlanNameDomain" xlink:to="loc_ptnCumulativeFromInceptionMember" order="11" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_EquityGrossProceedsShares" xlink:label="loc_ptnEquityGrossProceedsShares" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnEquityGrossProceedsShares" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProceedsFromOtherEquity" xlink:label="loc_us-gaapProceedsFromOtherEquity" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapProceedsFromOtherEquity" order="2" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_EquityFeesShares" xlink:label="loc_ptnEquityFeesShares" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnEquityFeesShares" order="3" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProceedsFromFeesReceived" xlink:label="loc_us-gaapProceedsFromFeesReceived" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapProceedsFromFeesReceived" order="4" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_EquityExpensesShares" xlink:label="loc_ptnEquityExpensesShares" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnEquityExpensesShares" order="5" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_EquityExpensesProceeds" xlink:label="loc_ptnEquityExpensesProceeds" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnEquityExpensesProceeds" order="6" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_EquityNetProceedsShares" xlink:label="loc_ptnEquityNetProceedsShares" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnEquityNetProceedsShares" order="7" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_EquityNetProceedsProceeds" xlink:label="loc_ptnEquityNetProceedsProceeds" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnEquityNetProceedsProceeds" order="8" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/RedeemableConvertiblePreferredStockEscrowedProceedsAndStockholdersEquityDetails1" xlink:title="000044 - Disclosure - REDEEMABLE CONVERTIBLE PREFERRED STOCK ESCROWED PROCEEDS AND STOCKHOLDERS EQUITY (Details 1)">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaapStatementLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaapStatementTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStatementTable" order="2000" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameAxis" xlink:label="loc_us-gaapPlanNameAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapPlanNameAxis" order="10" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaapPlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapPlanNameAxis" xlink:to="loc_us-gaapPlanNameDomain" order="20" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaapPlanNameDomain_10" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaapPlanNameAxis" xlink:to="loc_us-gaapPlanNameDomain_10" order="30" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_MayTwoThousandTwentyTwoWarrantsMember" xlink:label="loc_ptnMayTwoThousandTwentyTwoWarrantsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPlanNameDomain" xlink:to="loc_ptnMayTwoThousandTwentyTwoWarrantsMember" order="11" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_OctoberTwoThousandTwentyTwoPrivateWarrantsOneMember" xlink:label="loc_ptnOctoberTwoThousandTwentyTwoPrivateWarrantsOneMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPlanNameDomain" xlink:to="loc_ptnOctoberTwoThousandTwentyTwoPrivateWarrantsOneMember" order="12" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_OctoberTwoThousandTwentyTwoPlacementAgentWarrantsTwoMember" xlink:label="loc_ptnOctoberTwoThousandTwentyTwoPlacementAgentWarrantsTwoMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPlanNameDomain" xlink:to="loc_ptnOctoberTwoThousandTwentyTwoPlacementAgentWarrantsTwoMember" order="13" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_OctoberTwoZeroTwoThreePrivateWarrantsMember" xlink:label="loc_ptnOctoberTwoZeroTwoThreePrivateWarrantsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPlanNameDomain" xlink:to="loc_ptnOctoberTwoZeroTwoThreePrivateWarrantsMember" order="14" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_OctoberTwoZeroTwoThreePlacementAgentWarrantsMember" xlink:label="loc_ptnOctoberTwoZeroTwoThreePlacementAgentWarrantsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPlanNameDomain" xlink:to="loc_ptnOctoberTwoZeroTwoThreePlacementAgentWarrantsMember" order="15" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_JanuaryTwoZeroTwoFourPrivateWarrantsMember" xlink:label="loc_ptnJanuaryTwoZeroTwoFourPrivateWarrantsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPlanNameDomain" xlink:to="loc_ptnJanuaryTwoZeroTwoFourPrivateWarrantsMember" order="16" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_JanuaryTwoZeroTwoFourPlacementAgentWarrantsMember" xlink:label="loc_ptnJanuaryTwoZeroTwoFourPlacementAgentWarrantsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPlanNameDomain" xlink:to="loc_ptnJanuaryTwoZeroTwoFourPlacementAgentWarrantsMember" order="17" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_SharesOfCommonStock" xlink:label="loc_ptnSharesOfCommonStock" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnSharesOfCommonStock" order="1" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_ExercisePricePerShareWarrantsOutstanding" xlink:label="loc_ptnExercisePricePerShareWarrantsOutstanding" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnExercisePricePerShareWarrantsOutstanding" order="2" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_LatestTerminationDate" xlink:label="loc_ptnLatestTerminationDate" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnLatestTerminationDate" order="3" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/RedeemableConvertiblePreferredStockEscrowedProceedsAndStockholdersEquityDetails2" xlink:title="000045 - Disclosure - REDEEMABLE CONVERTIBLE PREFERRED STOCK ESCROWED PROCEEDS AND STOCKHOLDERS EQUITY (Details 2)" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/RedeemableConvertiblePreferredStockEscrowedProceedsAndStockholdersEquityDetails3" xlink:title="000046 - Disclosure - REDEEMABLE CONVERTIBLE PREFERRED STOCK ESCROWED PROCEEDS AND STOCKHOLDERS EQUITY (Details 3)" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/RedeemableConvertiblePreferredStockEscrowedProceedsAndStockholdersEquityDetails4" xlink:title="000047 - Disclosure - REDEEMABLE CONVERTIBLE PREFERRED STOCK ESCROWED PROCEEDS AND STOCKHOLDERS EQUITY (Details 4)" />
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/RedeemableConvertiblePreferredStockEscrowedProceedsAndStockholdersEquityDetailsNarrative" xlink:title="000048 - Disclosure - REDEEMABLE CONVERTIBLE PREFERRED STOCK ESCROWED PROCEEDS AND STOCKHOLDERS EQUITY (Details Narrative)">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaapStatementLineItems" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaapStatementTable" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStatementTable" order="2000" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaapAwardTypeAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapAwardTypeAxis" order="20" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" order="30" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" order="40" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameAxis" xlink:label="loc_us-gaapPlanNameAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapPlanNameAxis" order="30" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaapPlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapPlanNameAxis" xlink:to="loc_us-gaapPlanNameDomain" order="40" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaapPlanNameDomain_10" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaapPlanNameAxis" xlink:to="loc_us-gaapPlanNameDomain_10" order="50" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaapStatementClassOfStockAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapStatementClassOfStockAxis" order="40" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaapClassOfStockDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapStatementClassOfStockAxis" xlink:to="loc_us-gaapClassOfStockDomain" order="50" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaapClassOfStockDomain_10" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaapStatementClassOfStockAxis" xlink:to="loc_us-gaapClassOfStockDomain_10" order="60" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyTransactionAxis" xlink:label="loc_us-gaapRelatedPartyTransactionAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapRelatedPartyTransactionAxis" order="60" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyTransactionDomain" xlink:label="loc_us-gaapRelatedPartyTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapRelatedPartyTransactionAxis" xlink:to="loc_us-gaapRelatedPartyTransactionDomain" order="70" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyTransactionDomain" xlink:label="loc_us-gaapRelatedPartyTransactionDomain_10" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaapRelatedPartyTransactionAxis" xlink:to="loc_us-gaapRelatedPartyTransactionDomain_10" order="80" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="loc_us-gaapRelatedPartyTransactionsByRelatedPartyAxis" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapRelatedPartyTransactionsByRelatedPartyAxis" order="80" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaapRelatedPartyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapRelatedPartyTransactionsByRelatedPartyAxis" xlink:to="loc_us-gaapRelatedPartyDomain" order="90" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaapRelatedPartyDomain_10" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaapRelatedPartyTransactionsByRelatedPartyAxis" xlink:to="loc_us-gaapRelatedPartyDomain_10" order="100" xbrldt:contextElement="segment" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_TwentyTwentyThreeEquityDistributionAgreementMember" xlink:label="loc_ptnTwentyTwentyThreeEquityDistributionAgreementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_ptnTwentyTwentyThreeEquityDistributionAgreementMember" order="81" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_SecuritiesPurchaseAgreementPlanMember" xlink:label="loc_ptnSecuritiesPurchaseAgreementPlanMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPlanNameDomain" xlink:to="loc_ptnSecuritiesPurchaseAgreementPlanMember" order="82" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_SeriesBAndCRedeemableConvertiblePreferredStockMember" xlink:label="loc_ptnSeriesBAndCRedeemableConvertiblePreferredStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapClassOfStockDomain" xlink:to="loc_ptnSeriesBAndCRedeemableConvertiblePreferredStockMember" order="83" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_ExecutiveOfficersMember" xlink:label="loc_ptnExecutiveOfficersMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapRelatedPartyTransactionDomain" xlink:to="loc_ptnExecutiveOfficersMember" order="84" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_ConvertibleSeriesAPreferredStocksMember" xlink:label="loc_ptnConvertibleSeriesAPreferredStocksMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapClassOfStockDomain" xlink:to="loc_ptnConvertibleSeriesAPreferredStocksMember" order="85" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_SeriesBConvertiblePreferredStockMember" xlink:label="loc_ptnSeriesBConvertiblePreferredStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapClassOfStockDomain" xlink:to="loc_ptnSeriesBConvertiblePreferredStockMember" order="86" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_SecuritiesPurchaseAgreementMember" xlink:label="loc_ptnSecuritiesPurchaseAgreementMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPlanNameDomain" xlink:to="loc_ptnSecuritiesPurchaseAgreementMember" order="87" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_SeriesBRedeemableConvertiblePreferredStockMember" xlink:label="loc_ptnSeriesBRedeemableConvertiblePreferredStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapClassOfStockDomain" xlink:to="loc_ptnSeriesBRedeemableConvertiblePreferredStockMember" order="88" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_SeriesCRedeemableConvertiblePreferredStockMember" xlink:label="loc_ptnSeriesCRedeemableConvertiblePreferredStockMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapClassOfStockDomain" xlink:to="loc_ptnSeriesCRedeemableConvertiblePreferredStockMember" order="89" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_TwentyElevenStockIncentivePlanMember" xlink:label="loc_ptnTwentyElevenStockIncentivePlanMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPlanNameDomain" xlink:to="loc_ptnTwentyElevenStockIncentivePlanMember" order="90" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_PresidentMember" xlink:label="loc_srtPresidentMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapRelatedPartyDomain" xlink:to="loc_srtPresidentMember" order="91" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_CFOandCOOMember" xlink:label="loc_ptnCFOandCOOMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapRelatedPartyDomain" xlink:to="loc_ptnCFOandCOOMember" order="92" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_EquityDistributionAgreementDescription" xlink:label="loc_ptnEquityDistributionAgreementDescription" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnEquityDistributionAgreementDescription" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockOptionPlanExpense" xlink:label="loc_us-gaapStockOptionPlanExpense" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStockOptionPlanExpense" order="2" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_NumberOfShareVestingRestrictedUnits" xlink:label="loc_ptnNumberOfShareVestingRestrictedUnits" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnNumberOfShareVestingRestrictedUnits" order="3" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_AggregateValueOfShareVestingRestrictedUnits" xlink:label="loc_ptnAggregateValueOfShareVestingRestrictedUnits" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnAggregateValueOfShareVestingRestrictedUnits" order="4" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_WarrantToPurchaseCommonStock" xlink:label="loc_ptnWarrantToPurchaseCommonStock" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnWarrantToPurchaseCommonStock" order="5" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:label="loc_us-gaapClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" order="6" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CostsAndExpenses" xlink:label="loc_us-gaapCostsAndExpenses" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapCostsAndExpenses" order="7" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_GrossProceeds" xlink:label="loc_ptnGrossProceeds" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnGrossProceeds" order="8" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_VotingOfSharesDescription" xlink:label="loc_ptnVotingOfSharesDescription" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnVotingOfSharesDescription" order="9" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharesIssuedPricePerShare" xlink:label="loc_us-gaapSharesIssuedPricePerShare" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapSharesIssuedPricePerShare" order="10" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_DescriptionOfCommission" xlink:label="loc_ptnDescriptionOfCommission" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnDescriptionOfCommission" order="11" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_UnvestedPerformancesBasedRestrictedStockUnit" xlink:label="loc_ptnUnvestedPerformancesBasedRestrictedStockUnit" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnUnvestedPerformancesBasedRestrictedStockUnit" order="12" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_UnvestedPerformanceBasedStockOptionsGrantedToExecutiveOfficersAndOtherEmployees" xlink:label="loc_ptnUnvestedPerformanceBasedStockOptionsGrantedToExecutiveOfficersAndOtherEmployees" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnUnvestedPerformanceBasedStockOptionsGrantedToExecutiveOfficersAndOtherEmployees" order="13" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_UnvestedPerformanceBasedStockOptionsGranted" xlink:label="loc_ptnUnvestedPerformanceBasedStockOptionsGranted" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnUnvestedPerformanceBasedStockOptionsGranted" order="14" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockExpense" xlink:label="loc_us-gaapRestrictedStockExpense" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapRestrictedStockExpense" order="15" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVesteOutstandingNumber" xlink:label="loc_ptnShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVesteOutstandingNumber" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVesteOutstandingNumber" order="16" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_DescriptionOfSecuritiesPurchaseAgreement" xlink:label="loc_ptnDescriptionOfSecuritiesPurchaseAgreement" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnDescriptionOfSecuritiesPurchaseAgreement" order="17" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PreferredStockSharesOutstanding" xlink:label="loc_us-gaapPreferredStockSharesOutstanding" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapPreferredStockSharesOutstanding" order="18" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProceedsFromGrantors" xlink:label="loc_us-gaapProceedsFromGrantors" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapProceedsFromGrantors" order="19" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccountsReceivablePurchase" xlink:label="loc_us-gaapAccountsReceivablePurchase" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapAccountsReceivablePurchase" order="20" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LegalFees" xlink:label="loc_us-gaapLegalFees" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapLegalFees" order="21" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockRepurchasedDuringPeriodShares" xlink:label="loc_us-gaapStockRepurchasedDuringPeriodShares" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStockRepurchasedDuringPeriodShares" order="22" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProceedsFromIssuanceInitialPublicOffering" xlink:label="loc_us-gaapProceedsFromIssuanceInitialPublicOffering" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapProceedsFromIssuanceInitialPublicOffering" order="23" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquityOtherShares" xlink:label="loc_us-gaapStockholdersEquityOtherShares" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStockholdersEquityOtherShares" order="24" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharePrice" xlink:label="loc_us-gaapSharePrice" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapSharePrice" order="25" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_ExpiryOfShareIssuance" xlink:label="loc_ptnExpiryOfShareIssuance" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnExpiryOfShareIssuance" order="26" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_AggregateValue" xlink:label="loc_ptnAggregateValue" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnAggregateValue" order="27" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PreferredStockConvertibleConversionPrice" xlink:label="loc_us-gaapPreferredStockConvertibleConversionPrice" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapPreferredStockConvertibleConversionPrice" order="28" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentConvertibleLiquidationPreferencePerShare" xlink:label="loc_us-gaapDebtInstrumentConvertibleLiquidationPreferencePerShare" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapDebtInstrumentConvertibleLiquidationPreferencePerShare" order="29" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CashAvailableForDistributions" xlink:label="loc_us-gaapCashAvailableForDistributions" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapCashAvailableForDistributions" order="30" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_CashAvailableForDistributionsAdditional" xlink:label="loc_ptnCashAvailableForDistributionsAdditional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnCashAvailableForDistributionsAdditional" order="31" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_UnvestedPerformanceBasedRestrictedStockUnitsGranted" xlink:label="loc_ptnUnvestedPerformanceBasedRestrictedStockUnitsGranted" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnUnvestedPerformanceBasedRestrictedStockUnitsGranted" order="32" />
    <link:loc xlink:type="locator" xlink:href="ptn-20240331.xsd#ptn_ContributionOfNumberOfShare" xlink:label="loc_ptnContributionOfNumberOfShare" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_ptnContributionOfNumberOfShare" order="33" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SellingGeneralAndAdministrativeExpense" xlink:label="loc_us-gaapSellingGeneralAndAdministrativeExpense" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapSellingGeneralAndAdministrativeExpense" order="34" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueAdjustmentOfWarrants" xlink:label="loc_us-gaapFairValueAdjustmentOfWarrants" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapFairValueAdjustmentOfWarrants" order="35" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://ptn.com/role/IncomeTaxesDetailsNarrative" xlink:title="000049 - Disclosure - INCOME TAXES (Details Narrative)" />
</link:linkbase>
