Dammarane triterpenes of Trevoa Trinervis: Structure and absolute stereochemstry of trevoagennins A, B, and C1

Abstract

Trevoagenins A, B, and C, extracted from Trevoa trinervis Miers, are shown, by chemical and spectral means, to be isomeric dammarane triterpenes possessing the general 3,25,30-trihydroxy-(20,24)-epoxydammaran-16-one structure with stereoisomeric side-chains of the ocotillol type. Trevoagenin A (20R,24R)-(1), whose stereochemistry has been established by chemical methods and confirmed by X-ray analysis, was transformed into (20)R,24–ocotillone (26) and the C-24 stereochemistry was assigned as R. As a consequence, the C-24 stereochemistry for ocotillol-related compounds of the (20R)-series, unestablished so far, has been determined. The stereochemistry of trevoagenin B, (20S,24R)-(13), was established by chemical correlation with trevoagenin A. Moreover, trevoagenin B was transformed into ocotillol (20S,24R)-(21) and its recently questioned C-24 stereochemistry has been reaffirmed. Trevoagenin C, (20S,24S)-(17), is the C-24 isomer of trevoagenin B as shown by degradation of both compounds to the lactone (16).