Abstract
Stemmosides C and D, two novel pregnane glycosides characterized by an unusual C-17α side chain were isolated from the pericarps of
Solenostemma argel. In addition, stemmoside D displays an uncommon 14β proton configuration, apparently being the first pregnane isolated from plants known to have a 15 keto,
cis CD ring junction. Their structures have been established by ESIMS and NMR experiments. The relative configuration of the molecules was determined using a strategy based on the simulation of
1H,
13C, and
J coupling NMR parameters. DFT calculations of
1H and
13C chemical shifts, and of the
1H homonuclear spin–spin coupling constants were performed with the mPW1PW91 functional using the 6-31G(d,p) basis set on the fully optimized geometries of all the possible stereoisomers.
Graphical Abstract