15,21-Cyclowithanolides from Jaborosa bergii.

Six new withanolides (1-6) were isolated from the aerial parts of Jaborosa bergii plants and characterized by spectroscopic methods (1D and 2D NMR, MS). Five of the new compounds presented a novel norbornane-type structure in ring D of the steroid nucleus (1-5), resulting from a carbon-carbon bond between C-15 and C-21. The sixth withanolide isolated was the 5alpha-chloro-6beta-hydroxy analogue (6) of 2,3-dehydrojaborosalactol M (7), previously isolated from this plant. Compound 1 showed selective phytotoxicity toward monocotiledoneous and dicotiledoneous species.