Spiranoid withanolides from Jaborosa runcinata and Jaborosa araucana

From the aerial parts of Jaborosa runcinata six new withanolides were isolated and named jaborosalactones 1-6 (1-6). All contain a side chain with a carbon-carbon bond between C-12 of the intact steroid nucleus and C-23 and a spiranoid gamma-lactone at the latter position. The additional ring thus formed has a 17(20)-ene-22-keto system. Jaborosalactones 4-6 (4-6) also contain a hydroxyl group at C-21. From the aerial parts of Jaborosa araucana were isolated the known withanolides trechonolide A (8), its 5 alpha,6 beta-dihydroxy analogue jaborosotetrol (9), and the spiranoid withanolide jaborosalactone 2 (2), also isolated from J. runcinata. The stereochemistry of the spiranoid center at C-23 was determined as 23R based on NOESY NMR spectra and molecular modeling using the AM1 semiempirical method.