RESUMO
Eight new withanolides were isolated from the aerial parts of Vassobia lorentzii and characterized by spectroscopic methods and with the aid of molecular modeling. The compounds were identified as (17S,20R,22R)-5beta,6beta:18,20-diepoxy-18-hydro xy-1-oxowitha-2,5, 24-trienolide (1); (17S,20R,22R)-18,20-epoxy-4beta, 18-dihydroxy-1-oxowitha-2,5,24-trienolide (2); (17S,18R,20R, 22R)-4beta-hydroxy-18,20-epoxy-18-methoxy-1-oxowitha-2,5, 24-trienolide (3); (17S,18S,20R,22R)-4beta-hydroxy-18, 20-epoxy-18-methoxy-1-oxowitha-2,5,24-trienolide (4); (17S,20R, 22R)-4beta-hydroxy-18,20-epoxy-1,18-dioxowitha-2,5,24-tri enolide (5); (17S,18R,20R,22R)-18,20-epoxy-18-methoxy-1,4-dioxowitha++ +-2,5, 24-trienolide (6); (17S,18S,20R,22R)-18,20-epoxy-18-methoxy-1, 4-dioxowitha-2,5,24-trienolide (7); and (17S,20R,22R)-5beta, 6beta-epoxy-4beta,18,20-trihydroxy-1-oxowitha-2,24-die nolide (8). Compounds 1 and 2 were obtained as epimeric mixtures at C-18.