title: 18,20-Hemiacetal-type and other withanolides from dunalia brachyacantha
abstract: 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.
authors.affiliation: 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.
authors.initials: GL
authors.lastname: Silva
authors.initials: G
authors.lastname: Burton
authors.initials: JC
authors.lastname: Oberti