Note 2 — Stock-Based Compensation

As of March 31, 2016, the Company had two stock-based employee compensation plans, the Stock Incentive Plan (“Incentive Plan”) and the Employee Stock Purchase Plan (“ESPP”), both which were amended and restated in March 2014 and approved by the Company’s stockholders in May 2014. Stock-based compensation expense of $2,645 ($2,556 of expense related to the Incentive Plan and $89 of expense related to the ESPP) was recognized during the first three months of 2016, while $2,259 ($2,165 of expense related to the Incentive Plan and $94 of expense related to the ESPP) was recognized during the first three months of 2015.

There was approximately $16,164 of total unrecognized compensation cost related to non-vested stock option awards and restricted stock unit awards granted by the Company as of March 31, 2016. That cost is expected to be recognized as follows: $4,840 during the remainder of 2016, $5,856 in 2017, $3,796 in 2018 and $1,672 in 2019. In addition, the Company has outstanding performance-based stock options for which no compensation expense is recognized until “performance” has occurred and the award vests. At the time of vesting, compensation expense will be recognized.

Stock Incentive Plan

The Company grants stock option awards and restricted stock unit awards to its employees, directors, and consultants under the Incentive Plan. Under the Incentive Plan, stock option awards are granted with an exercise price equal to the market price of the Company’s stock at the date of grant. Since March 1, 2011, stock option awards granted to employees generally vest 25% each year until fully vested after four years. In January 2013, the Company made retention grants of stock option awards and restricted stock units. These awards vest 50% each year until fully vested after two years. In August 2013 and December 2014, the Company issued 1,032 and 1,250 performance-based stock options, respectively. These awards vest upon successful completion of specific development milestones. As of March 31, 2016, 75% of the August 2013 grants have vested based upon achievement of three milestones: (1) successful completion of the OPuS-1 clinical trial, for which vesting occurred in the second quarter of 2014, (2) FDA approval of RAPIVAB for which vesting occurred in the fourth quarter of 2014, and (3) initiation of a Phase 1 clinical trial to evaluate the safety, pharmacokinetics and pharmacodynamics of orally-administered BCX7353 in healthy volunteers, for which vesting occurred in the second quarter of 2015. Thus, as of March 31, 2016, 25% of the August 2013 performance-based grants and 100% of the December 2014 performance-based grants remain unvested and no compensation expense has been recognized for these portions of the previously issued performance-based grants. Stock option awards granted to non-employee directors of the Company generally vest monthly over one year. All stock option awards have contractual terms of 5 to 10 years. The vesting exercise provisions of all awards granted under the Incentive Plan are subject to acceleration in the event of certain stockholder-approved transactions, or upon the occurrence of a change in control as defined in the Incentive Plan.

Related activity under the Incentive Plan is as follows:

	Awards Available			Options Outstanding			Weighted Average Exercise Price
Balance December 31, 2015		16			10,671		$	7.50
Restricted stock unit awards granted		(13	)		—			—
Restricted stock unit awards cancelled		15			—			—
Stock option awards granted		—			—			—
Stock option awards exercised		—			(79	)		2.32
Stock option awards cancelled		109			(109	)		9.58

Balance March 31, 2016		127			10,483		$	7.51

No stock option awards were granted under the Incentive Plan during the first three months of 2016.

Employee Stock Purchase Plan (“ESPP”)

The Company has reserved a total of 1,475 shares of common stock to be purchased under the ESPP, of which 463 shares remain available for purchase at March 31, 2016. Eligible employees may authorize up to 15% of their salary to purchase common stock at the lower of 85% of the beginning or 85% of the ending price during six-month purchase intervals. No more than 3 shares may be purchased by any one employee at the six-month purchase dates and no employee may purchase stock having a fair market value at the commencement date of $25 or more in any one calendar year. The Company issued 34 shares during the first three months of 2016 under the ESPP. Compensation expense for shares purchased under the ESPP related to the purchase discount and the “look-back” option were determined using a Black-Scholes option pricing model.