Constituents of plants of the family Asclepiadaceae : constituents of Marsdenia flavescens and Marsdenia restrata from the Wollongong area

The steroidal and diterpenoidal constituents of two Marsdenia species, M. flavescens and M. rostrata^ of the plant family Asclepiadaceae were investigated. Both species were collected from the slopes of Mount Keira on the Illawarra escarpment of New South Wales. Extraction of the whole plant of M^, f lave s cens. which does not contain any alkaloids, yielded different components from two separate collections made during different seasons of 1970 and 1971. From the 1970 collection a new steroid, named flavescin was isolated. Its structure was elucidated on the basis of spectroscopic evidence - especially that obtained by mass and nuclear magnetic resonance spectroscopy - as 12 - 0 - acetyl - 12^, 14^, 20"J - pentahydroxy - ¿^ - pregnen - 1 - one. From the second collection two new diterpenes, designated as diterpene I and diterpene II, were isolated. Biogenetic considerations, together with an examination of the mass spectral fragmentation patterns, lead to the tentative assignment of the new tetracyclic diterpene structures 24. and 2^ to these compounds. Flavescin also was shown to be present. The non-alkaloidal portion of a M^ rostrata extract yielded two new polyhydroxypregnane type steroids. Evidence indicates that rostragenin I possesses hydroxy groups in the 16- and 17- positions. The structure of rostragenin II was elucidated with the help of mass and nuclear magnetic resonance spectroscopy as 5