Syntheses and biological evaluation of ring-C modified colchicine analogs.

Ring-C modified alkaloids were synthesized from colchicine using iminonitroso Diels-Alder reactions in a highly regio- and stereoselective fashion. Several analogs exhibited cytotoxic activity similar to that of colchicine itself against PC-3 and MCF-7 cancer cell lines, by serving as prodrugs of colchicine through retro Diels-Alder reactions under the assayed conditions. In vitro microtubule polymerization assays indicated that these modifications affected their interaction with tubulin.