18-20-hemiacetal-type and other withanolides from Dunalia brachyacantha

Two Dunalia brachyacantha specimens collected at different locations in Arg entina were investigated separately. The 18,20-hemiacetal-type withanolides (17S,20R,22R,24S,25R)-4 beta-acetylaxy-5 beta,6 beta:18,20-diepoxy-18-hydr oxy-1-oxowitha-2-enolide (1) and (17S,20R,22R)-4 beta-acetyloxy-5 beta,6 be ta:18,20-diepoxy-18-hydroxy-1-oxowitha-2,24-dienolide (2) were isolated fro m the first collection, both as mixtures epimeric at C-18. The second colle ction contained instead (17R,20S,22R)-5 beta,6 beta-epoxy-4 beta,16 alpha-d ihydroxy-1-oxowitha-2,24-dienolide (3); (17R,20S,22R)-5 beta,6 beta-epoxy-4 beta, 18-dihydroxy-1-oxowitha-2,24-dienolide (4), and (17R, 20S,22R)-5 bet a,6 beta-epoxy-4 beta,16 alpha-dihydroxy-1,18-dioxowitha-2,24-dienolide (5) . All five new withanolides (1-5) bear an A and B ring substitution pattern similar to that of withaferin A, and their structural elucidation was achi eved by spectroscopic techniques.