During 2016, 2015 and 2014, we paid interest aggregating $5.5 million, $4.6 million and $2.9 million, respectively. Interest paid during 2016 included collection fees of $778,000 and a prepayment premium of $2.1 million, both of which were withdrawn by CRG from a bank account under their control. During 2016, 2015, and 2014, we issued 67,002, 68,157 and 36,455 shares of our common stock, respectively, as matching contributions to our 401(k) Plan which were valued at $121,000, $117,000 and $100,000, respectively. In December 2016, we prepaid $348,000 of insurance premiums through the issuance of a note payable to IPFS with an interest rate of 8.99%. During 2015 and 2014, we recorded $1.0 million and $2.4 million, respectively, of end-of-term fees associated with our notes payable to CRG and Oxford.

In connection with their initial investment in March 2015, the investors in MT were issued warrants that have been determined to be derivative liabilities with an estimated fair value of $63,000. A $46,000 deemed dividend related to the beneficial conversion feature within the MT Preferred Stock was also recorded at the time of the initial investment in MT. See Note 9.

During 2014, in connection with the Oxford Loan Agreement, we issued warrants with an estimated relative fair value of $465,000. Also during 2014, in connection with entering into the R-NAV joint enterprise, Navidea executed a promissory note in the principal amount of $666,666, payable in two equal installments on July 15, 2015 and July 15, 2016, the first and second anniversaries of the R-NAV transaction. See Note 10.