Studies on Indian medicinal plants. Part 77. Structure and stereochemistry of some new steroidal alkaloids from Solanum pseudocapsicum and Solanum giganteum by nuclear magnetic resonance spectroscopy
Three new stereoisomeric Steroidal alkaloids, viz. solacapine (6), episolacapine (11), and isosolacapine (13), along with another hitherto unreported base, O-methylsolanocapsine (3), have been isolated from the arboreal part of Solanum pseudocapsicum Linn. They have been characterised as (20S, 22R, 23S, 25R)-, (20S, 22R, 23R, 25R)-, and (20S, 22S, 23S, 25R)-3β-amino-16α,23-dihydroxy-22,26-epimino-5α-cholestanes, respectively, primarily based on 1H and 13C n.m.r. spectra. The structures of (3), (6), and (11) could be confirmed by correlation with solanocapsine (1). Isosolacapine (13) turned out to be the first 22,26-epiminocholestane derivative encountered in nature with 22βN stereochemistry. A diagnostic down-field shift of the C-22 resonance frequency in the 13C n.m.r. spectra of 22βN-22,26-epiminocholestanes by ca. 3 p.p.m. relative to those of the corresponding 22αN-isomers has been observed. The C-25 stereochemistry of solanogantamine (28) and isosolanogantamine (29), the stereoisomeric 3-amino solanidanes isolated from Solanum gigantem Jacq., has also been established.