Withanolides from Vassobia lorentzii

Abstract

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)-5β,6β:18,20-diepoxy-18-hydroxy-1-oxowitha-2,5,24-trienolide (1); (17S,20R,22R)-18,20-epoxy-4β,18-dihydroxy-1-oxowitha-2,5,24-trienolide (2); (17S,18R,20R,22R)-4β-hydroxy-18,20-epoxy-18-methoxy-1-oxowitha-2,5,24-trieno lide (3); (17S,18S,20R,22R)-4β-hydroxy-18,20-epoxy-18-methoxy-1-oxowitha-2,5,24-trieno lide (4); (17S,20R,22R)-4β-hydroxy-18,20-epoxy-1,18-dioxowitha-2,5,24-trienolide (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)-5β,6β-epoxy-4β,18,20-trihydroxy-1-oxowitha-2,24-dienolide (8). Compounds 1 and 2 were obtained as epimeric mixtures at C-18.