Tigliane diterpenes from the latex of Euphorbia obtusifolia with inhibitory activity on the mammalian mitochondrial respiratory chain.

Six diterpenes isolated from the latex of Euphorbia obtusifolia Poir. (Euphorbiaceae) were evaluated for their inhibition of the NADH oxidase activity in submitochondrial particles from beef heart. 4,20-Dideoxyphorbol-12,13-bis(isobutyrate) was the most potent inhibitor and showed an inhibitory concentration with IC(50) value of 2.6+/-0.3mM. In the present study, some structure-activity trends are suggested for the inhibitory activity of the mammalian mitochondrial respiratory chain of these natural product derivatives of 4-deoxyphorbol esters.