Scaffold-hopping strategy toward calanolides with nitrogen-containing heterocycles

(+)-Calanolide A was the first natural product identified as an active agent against HIV-1 and Mycobacterium tuberculosis (Mtb). In devising a scaffold-hopping strategy of structure modification of (+)-calanolide A, we focused on the synthesis of calanolides by replacing ring D with various five or six membered nitrogen-containing heterocycles, hoping to get further understanding of the structure–activity relationship.