F. Capitalization and Warrant Liability

Capitalization

At both December 31, 2016 and 2015, we had 150.0 million shares of common stock and 10.0 million shares of undesignated preferred stock authorized. No shares of preferred stock have been issued as of December 31, 2016.

The following shares of common stock were reserved for future issuance:

 

		December 31
		2016				2015
Stock-based compensation plans			17,940,618				8,838,165
Warrants to purchase common stock — 2011 offering			—				1,310,000
Warrants to purchase common stock — 2012 offering			1,893,527				2,054,893
Warrants to purchase common stock — 2014 offering			—				1,500,000
			19,834,145				13,703,058

As of December 31, 2016, the outstanding warrants to purchase shares of common stock had an exercise price of $1.01 per share and expire in March 2017. As of December 31, 2016, warrants to purchase an aggregate of 2,454,300 shares of common stock have been exercised, resulting in aggregate proceeds of approximately $2.5 million.

In 2014, we completed a registered direct offering generating net proceeds of approximately $18.8 million through the issuance of 5,000,000 shares of common stock and immediately exercisable warrants to purchase 1,500,000 shares of common stock with an exercise price of $4.50 per share that expired in July 2016. The securities were sold in multiples of a fixed combination of one share of common stock and a warrant to purchase 0.30 shares of common stock at an offering price of $4.10 per fixed combination.

 

Aspire Capital

We have had an equity purchase arrangement in place with Aspire Capital since 2011, through two-to-three year equity facility agreements, each with similar terms. The current agreement with Aspire Capital was entered into in December 2015 and includes Aspire’s commitment to purchase up to an aggregate of $30.0 million of shares of our common stock over a three-year period. The terms of the 2015 equity facility are similar to the previous arrangements, and we issued 250,000 shares of our common stock to Aspire Capital as a commitment fee in December 2015 and filed a registration statement for the resale of 16,600,000 shares of common stock in connection with the new equity facility. During the years ended December 31, 2016, 2015 and 2014, we sold 2,191,418, 4,023,719, and 250,000 shares, respectively, to Aspire Capital at average prices of $1.84, $2.58 and $3.78 per share, respectively. As of December 31, 2016, we have received proceeds of approximately $28.8 million in aggregate under the Aspire equity purchase agreements since its inception in 2011.

Warrant Liabilities

The warrants issued in the January 2014 registered direct offering that are now expired contained a provision for a cash payment in the event that the shares are not delivered to the holder within two trading days, which never occurred. The warrants issued in both the March 2012 private placement and the February 2011 registered direct offering, which are now expired, each contained a provision for net cash settlement in the event of a fundamental transaction (e.g., merger, sale of substantially all assets, tender offer, or share exchange). If a fundamental transaction occurs in which the consideration issued consists of all cash or stock in a non-public company, then the warrant holder has the option to receive cash equal to a Black Scholes value of the remaining unexercised portion of the warrant. Further, the March 2012 warrants include price protection in the event we sell stock below the exercise price, as defined, and the exercise price was reduced in February 2013 to $1.01 per share as a result of the October 2012 public offering.

The warrants have been classified as liabilities, as opposed to equity, due to the potential adjustment to the exercise price that could result upon late delivery of the shares or potential cash settlement upon the occurrence of certain events as described above, and are recorded at their fair values at each balance sheet date.