At December 31, 2013, outstanding warrants to purchase shares of common stock are as follows:
| Warrants | Exercise Price | Expiration Date | ||||||
| 99,696 | $ | 11.9125 | June 2014 | |||||
| 144,000 | $ | 5.8750 | October 2014 | |||||
| 19,007 | $ | 4.4750 | July 2014 | |||||
| 14,183 | $ | 4.0625 | August 2014 | |||||
| 36,071 | $ | 3.7500 | June 2014 | |||||
| 216,000 | $ | 3.6700 | October 2014 | |||||
| 1,816,608 | $ | 3.6500 | May 2015 | |||||
| 409,228 | $ | 3.4400 | April 2015 | |||||
| 2,046,139 | $ | 2.7500 | January 2016 | |||||
| 1,062,500 | $ | 1.0000 | April 2015 | |||||
| 10,625,000 | $ | 1.1000 | November 2016 | |||||
| 28,097,500 | $ | 0.6500 | June 2018 | |||||
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| 44,585,932 | ||||||||
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