Synthetic study of cnicin: Synthesis of the side chain and its esterification

Cnicin is a germacranolide sesquiterpene lactone that possesses potent inhibitory activity against the protozoan parasite Trypanosoma brucei, which causes human African trypanosomiasis (HAT). Although cnicin has an interesting structure and attractive biological activity, synthetic studies of cnicin have not yet been reported. This report describes the synthesis of the protected side chain carboxylic acid moiety at C8 of cnicin via two routes starting from l-ascorbic acid. In addition, esterification between the synthetic side chain and salonitenolide derivative, which can be achieved via hydrolysis of cnicin and protection of the primary alcohol, was conducted. Thus, a semi-synthesis of cnicin was achieved.