Withanolides from Vassobia lorentzii

Eight new withanolides were isolated from the aerial parts of Vassobia lore ntzii and characterized by spectroscopic methods and with the aid of molecu lar modeling. The compounds were identified as (17S,20R,22R)-5 beta ,6 beta :18,20;-diepoxy-18-hydroxy-1-oxowitha-2,5,24-trienolide (1); (17S,20R,22R) -18,20-epoxy-4 beta ,18-dihydroxy-1-oxowitha-2,5,24- trienolide (2); (17S,1 8R,20R,22R)-4 beta -hydroxy-18,20-epoxy-18-methoxy-1-oxowitha-2,5,24-trieno lide (3); (17S,18S,20R,22R)-4 beta -hydroxy-18,20-epoxy-18-methoxy-1- oxowi tha-2,5,24-trienolide. (4); (17S,20R,22R)-4 beta -hydroxy-18,20-epoxy-1,18- dioxowitha-2,5,24-trienolide (5); (17S,18R,20R,22R)-18,20-epoxy-1-methoxy-1 ,4-dioxowitha-2,5,24-trienolide (6); (17S,18S,20R,22R)18,20-epoxy-18-methox y-1,4-dioxowitha-2,5,24-trienolide (7); and (17S,20R,22R)-5 beta ,6 beta -e poxy-4 beta, 18,20-trihyhroxy-1-oxowitha-2,24-dienolide (8). Compounds 1 an d 2 were obtained as epimeric-mixtures at C-18.