Cytotoxic 20,24-epoxywithanolides from Physalis angulata

A new withanolide, physangulide B (1), was isolated from calyxes of Physalis angulata. This compound was also present in the aerial parts along with the known physangulide (4), which was isolated as the acetonide 3, and 24,25-epoxywithanolide D (6). Structures of these compounds were determined by analysis of their spectroscopic data, which indicated the presence of a 20,24-epoxy group in both physangulides. The structures of compounds 1 and 6 were confirmed by X-ray analysis of their corresponding acetyl derivatives 2 and 7. The structure of physangulide was originally described as the 22S withanolide 5, now its structure and configuration are revised to 4. Evaluation of the cytotoxic activity of compounds 1-3 against two human cancer cell lines indicated a potent activity of compound 1 and its derivative 2.