Income Taxes (Tables)

12 Months Ended

Dec. 31, 2021

The difference between income taxes computed using the U.S. federal income effective tax rate and the provision for income taxes is as follows (in thousands):

	Year Ended December 31,
	2021			2020
Federal statutory rate	$	4,139		$	(8,278	)
State tax benefit		812			(1,740	)
Change in valuation allowance		(288	)		787
Tetraphase net operating losses and other adjustments		(4,670	)		-
Share-based compensation expense		565			9,072
State rate true-up		(369	)		291
Research and development credits		-			(173	)
Other permanent differences		(140	)		41
Provision for income taxes	$	49		$	-

Schedule of Significant Components Deferred Tax Assets

Deferred tax assets are as follows (in thousands):

	December 31,
	2021			2020
Deferred tax assets:
Net operating loss carryforwards	$	84,571		$	84,827
Research and development credits		24,015			24,179
Deferred royalty obligation		36,687			36,265
Share-based compensation expense		2,742			2,497
Depreciation and amortization expense		482			1,044
Lease liability		80			136
Capital loss carryforward		126			-
Other		337			436
Total gross deferred tax assets		149,040			149,384
Deferred tax liabilities:
Right-of-use lease asset		(80	)		(136	)
Valuation allowance		(148,960	)		(149,248	)
Net deferred tax assets	$	-		$	-