Cytotoxic 20,24-epoxywithanolides from Physalis angulata

• One new 20,24-epoxywithanolide and two known withanolides were isolated.
• This is the first report on the occurrence of 20,24-epoxywithanolides.
• The structure of the previously isolated physangulide is revised.
• The structures of 24,25-epoxywithanolide D and physangulide B were confirmed by X-ray analysis.
• Physangulide B and its acetyl derivative showed a strong cytotoxicity.

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.

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