Technically it doesn’t sound like a loan. What you did was you essentially created an equity investment with a preferred return from operating cash flow (monthly/quarterly depending on the duration), and distribution on a capital event.
This structure is pretty typical for a multi-investor structure where a LLC is formed and a K-1 is issues each year.
Could you claim capital gains on the portion above the loan interest? That would depend on how you structured the initial investment and how that is viewed by the IRS.
Though I doubt you could run into a problem by paying the income tax rate. You could construe it as a deferred interest payable at the capital event.
