Peracid oxidation products of swertanone, the novel triterpene of Swertiachirata

While treatment of swertanone (1a) with mineral acids and Lewis acids yielded isoswertanone (2a) as the only isolable product, its reaction with m-chloroperbenzoic acid afforded 7-alpha, 8-alpha-epoxyswertanone (7), 7-alpha -hydroxy-swert-8-en-3-one (8), swerta-7, 9(11)-dien-3-one (3a), its 7-alpha, 8-alpha -epoxide (4a), 7-alpha -hydroxy-friedogammacer-14-en-3-one (5a) and its 14-alpha, 15-alpha -epoxide (6a). The structures of the products have been elucidated mainly on the basis of H-1 and C-13 NMR spectroscopy and, in some cases, by chemical correlation. Assignments of C-13 NMR signals of the products have been done and those of some of the signals of 1a, swertenyl acetate (1b) and swertenol (16) have been revised. In this connection, spectra of bauerenyl acetate (18), isobauerenyl acetate (19) and multiflorenyl acetate (20) have been recorded.