Variation of the antimicrobial activity of Pseudognaphalium vira vira (Asteraceae): isolation and X-ray structure of ent-3beta-hydroxy-16-kauren-19-oic acid.

The antimicrobial properties of the resinous exudate from twigs and leaves of a population of Pseudognaphalium vira vira were re-examined against five Gram positive bacteria. The observed decrease in the antimicrobial activity might reflect a change in the diterpenoid composition of the exudate. The title compound 2 was isolated in substantial amount, together with ent-16-kauren-19-oic acid (1), and its structure determined by X-ray diffraction analysis.