In connection with the 2021 Private Placement Financing, we issued to the investors in the 2021 Private Placement Financing an aggregate of 43,125,004 shares of Common Stock and Series K Warrants to acquire up to an additional 32,343,754 shares of Common Stock at an exercise price of $0.17 per share. In addition, we also issued designees of the Placement Agent Placement Agent Warrants to acquire up to 3,234,375 shares of Common Stock at an exercise price of $0.20 per share. As of December 16, 2021, up to 32,343,754 shares may be acquired upon the exercise of the Series K Warrants and up to 3,234,375 shares may be acquired upon the exercise of the Placement Agent Warrants.
In June 2020, we issued certain of holders of our Series D Warrants Series J Warrants to acquire up to 3,886,364 shares of our Common Stock at an initial exercise price of $0.25 per share as consideration for those holders exercising their Series D Warrants in full to acquire 5,181,819 shares of our Common Stock at $0.18 per share. As of December 16, 2021, up to 3,886,364 shares may be acquired upon the exercise of the Series J Warrants.
In connection with the October 2019 Financing that closed on October 18, 2019, we issued an aggregate of 14,285,714 shares of our Common Stock, which equaled approximately 8% of the 173,577,233 shares of our Common Stock that were issued and outstanding immediately prior to the commencement of the October 2019 Financing. Upon the closing of the October 2019 Financing, we also issued Series I Warrants to acquire up to an additional 14,285,714 shares of our Common Stock at an initial exercise price of $0.22 per share and additional warrants to acquire up to an additional 1,071,429 shares of our Common Stock at an initial exercise price of $0.21875 per share to designees of the Placement Agent (the “2019 Placement Agent Warrants”). As of December 16, 2021, up to 14,285,714 shares may be acquired upon the exercise of the Series I Warrants and up to 1,071,429 shares may be acquired upon the exercise of the 2019 Placement Agent Warrants.
In connection with the financing that closed on May 14, 2019 (the “2019 Financing”), we issued an aggregate of 8,615,384 shares of our Common Stock, which equaled approximately 5% of the 164,961,849 shares of our Common Stock that were issued and outstanding immediately prior to the commencement of the 2019 Financing. Upon the closing of the 2019 Financing, we also issued Series H Warrants to acquire up to an additional 8,615,384 shares of our Common Stock at an initial exercise price of $0.40 per share. As of December 16, 2021, up to 8,615,384 shares may be acquired upon the exercise of the Series H Warrants.
In connection with the 2018 Financing that closed on July 2, 2018, we issued an aggregate of 9,070,000 shares of our Common Stock, which equaled approximately 6% of the 154,052,013 shares of our Common Stock that were issued and outstanding immediately prior to the commencement of the 2018 Financing. Upon the closing of the 2018 Financing, we also issued Series G Warrants to acquire up to an additional 6,802,500 shares of our Common Stock at an initial exercise price of $0.70 per share. As of December 16, 2021, up to 6,802,500 shares may be acquired upon the exercise of the Series G Warrants.
In connection with the 2017 Financing that closed on February 24, 2017, we issued an aggregate of 10,166,664 shares of our Common Stock, which equaled approximately 7% of the 136,745,712 shares of our Common Stock that were issued and outstanding immediately prior to the commencement of the 2017 Financing. Upon the closing of the 2017 Financing, we also issued Series F Warrants to acquire up to an additional 5,591,664 shares of our Common Stock at an initial exercise price of $0.75 per share. As of December 16, 2021, up to 5,591,664 shares may be acquired upon the exercise of the Series F Warrants.
In connection with the 2016 Private Placement Financing that closed on May 26, 2016, we issued an aggregate of 9,418,334 shares of our Common Stock, which equaled approximately 8% of the 118,592,070 shares of our Common Stock that were issued and outstanding immediately prior to the commencement of the 2016 Private Placement Financing. Upon the closing of the 2016 Private Placement Financing, we also issued Series E Warrants to acquire up to an additional 7,063,748 shares of our Common Stock at an initial exercise price of $0.4380 per share. As of December 16, 2021, the Series E warrants expired.
In addition to the aforementioned warrants, in June 2020 and November 2020, we issued $550,000 and $1,050,000 in aggregate principal amount of our Series 1 Unsecured Convertible Promissory Notes and Series 2 Unsecured Convertible Promissory Notes, respectively (collectively, the “Convertible Notes”). The Convertible Notes (i) have a three year term; (ii) accrue interest on the unpaid principal balance at a rate equal to ten percent (10.0%), and (iii) can be converted into shares of our Common Stock at a conversion price of $0.27 per share and $0.25 per share, respectively. At maturity, at our sole option, we may convert the principal and accrued interest under the Convertible Notes (the “Note Obligations”) into shares of our Common Stock at the applicable conversion price in lieu of repaying the Convertible Notes; provided, however, in the event we exercise this option, the Note Obligations will be deemed to equal the product of 1.35 and the outstanding Note Obligations.
Additionally, as of December 16, 2021, 4,278,356 shares of Common Stock were reserved for future issuance under the 2013 Plan, of which 24,899,014 shares are subject to outstanding option awards granted under the 2013 Plan at exercise prices ranging from $0.09