It's because the due date for Nasrat to get paid for the Trimipramine ANDA came around.
And this due date has been in the SEC filings for YEARS.
Good grief...
Here's the 10-K all the way back from 2017:
Trimipramine Acquisition
On May 16, 2017, we executed an asset purchase agreement with Mikah Pharma,and acquired from Mikah Pharma (the “Trimipramine Acquisition”) an FDA approved ANDA for Trimipramine for aggregate consideration of $1,200,000, payable pursuant to a senior secured note due on December 31, 2020 (the “Trimipramine Note”). Mikah Pharma is owned by Nasrat Hakim, the Chairman of the Board of Directors, President and Chief Executive Officer (CEO) of the Company. The Trimipramine Note bears interest at the rate of 10% per annum, payable quarterly. All principal and unpaid interest is due and payable on December 31, 2020. Pursuant to a security agreement, repayment of the Note is secured by the ANDA acquired in the Acquisition