Euphosalicin, a new diterpene polyester with multidrug resistance reversing activity from Euphorbia salicifolia

A novel diterpene polyester, named euphosalicin (1), the first representative of a new class of bicyclic diterpenes, was isolated from the dichloromethane extract of the whole plant of Euphorbia salicifolia, together with one known (2) and two new jatrophane diterpenes (3, 4). The new carbon skeleton is formally derived from the jatrophane framework by incorporation of a geminal methyl group in the ring system. Compound 1 was found to be more active than verapamil in reversing multidrug resistance in mouse lymphoma cells.