18,20-Hemiacetal-type and other withanolides from dunalia brachyacantha
Two Dunalia brachyacantha specimens collected at different locations in Argentina were investigated separately. The 18,20-hemiacetal-type withanolides (17S,20R,22R,24S,25R)-4beta-acetyloxy-5beta,6beta:18, 20-diepoxy-18-hydroxy-1-oxowitha-2-enolide (1) and (17S,20R, 22R)-4beta-acetyloxy-5beta,6beta:18, 20-diepoxy-18-hydroxy-1-oxowitha-2,24-dienolide (2) were isolated from the first collection, both as mixtures epimeric at C-18. The second collection contained instead (17R,20S,22R)-5beta, 6beta-epoxy-4beta,16alpha-dihydroxy-1-oxowitha-2,24-dienolide (3); (17R,20S,22R)-5beta,6beta-epoxy-4beta,18-dihydroxy-1-oxowitha-2, 24-dienolide (4), and (17R,20S,22R)-5beta,6beta-epoxy-4beta, 16alpha-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 achieved by spectroscopic techniques.
Silva
GL
Departamento de Quimica Organica and IMBIV, Facultad de Ciencias Quimicas, Universidad Nacional de Cordoba, Ciudad Universitaria, 5000 Cordoba, Argentina, and Departamento de Quimica Organica, Facultad de Ciencias Exactas y Naturales, Univ.
Burton
G
Oberti
JC