Major skin-irritant principle from Synadenium grantii.

The latex of Synadenium grantii Hook. f. (Euphorbiaceae) yielded a novel skin irritant, 12-O-tigloyl-4-deoxyphorbol-13-isobutyrate (I). The identity of the diterpene parent alcohol and the relative positions of the esterifying groups were established by spectral analysis and experiments leading to the hydrolysis and acetylation of I. Compound I is the first phorbol derivative to be reported from the genus Synadenium.