| Abstract
| - Twelve new withanolides were isolated from the aerial part of Jaborosa rotacea: five had a spiranoid δ-lactone (1−5);one contained a 26,12-δ-lactone and a C-12−C-23 bond (6); five corresponded to trechonolide-type withanolides withconfiguration at C-23 opposite of those previously isolated (7, 8, 10−12); two of these have an additional oxido-bridgebetween C-21 and C-24; finally a withanolide with a hemiketal ring formed between a 21-hydroxyl and a 12-ketone(13) and the closely related jaborosalactone R were also isolated. New compounds were fully characterized by acombination of spectroscopic methods (1D and 2D NMR and MS). The structures of the spiranoid withanolide and ofthe epimer of trechonolide A were confirmed by X-ray diffraction studies. Compounds 4, 5, 6, and 8 showed selectivephytotoxicity toward monocotyledoneous and dicotyledoneous species.
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