Longipinane derivatives from Stevia connata

The hexane extracts of the roots of Stevia connata afforded three new longi pinene derivatives, longipinane-7 beta,8 alpha,9 alpha-triol-1-one 7-angela te-8-methylbutyrate (1), longipin-2-ene-7 beta,8 alpha,9 alpha-triol-1-one 8,9-diangelate (6), and longipin-2-ene-7 beta,8 alpha,9 alpha-triol-1-one 8 -angelate-9-methylbutyrate (8), together with the known longipinane-7 beta, 8 alpha,9 alpha-triol-1-one 8,9-diangelate (2), longipinane-7 beta,8 alpha, 9 alpha-triol-1-one 7,9-diangelate (3), longipinane-7 beta,8 alpha,9 alpha- triol-1-one 7,8-diangelate (4), longipin-2-ene-7 beta,8 alpha,9 alpha-triol -1-one 7,8-diangelate (5), longipin-2-ene-7 beta,8 alpha,9 alpha-triol-1-on e 7-angelate-8-methylbutyrate (12), and stigmasterol. The structures of the new compounds were determined by chemical transformations and spectral met hods including 2D NMR measurements. Spontaneous intramolecular transesterif ications starting from the 7-angelate-9-methylbutyrate 8 provided an equili brated mixture of the 7-angelate-9-methylbutyrate 10, the 7-angelate-8-meth ylbutyrate 12 and the starting material when stored in MeOH-H2O solution, w hile the 8,9-diangelate 6 only provided a binary mixture of the 7,9-diangel ate 7 and the starting material under the same conditions. The structures o f 6-8, 10, and 12 and those of the nonisolable reaction intermediates 9, 11 , and 14 were further evaluated by AM1 semiempirical calculations.