Skin irritants of the sun spurge (Euphorbia helioscopia L.).

Euphorbia helioscopia is a common herbaceous week found in the British Isles and parts of Europe. It has been responsible for poisoning of livestock resulting in severe inflammation particularly of mucous membranes and the eyes. Four esters of 12-deoxyphorbol were isolated from the fresh aerial parts of the plant and their irritant doses 50% (I.D.50) ascertained using female L.A.C.A. mice, 12-Deoxyphorbol-13-phenylacetate-20-acetate was found to be the major component of the toxic fraction and occurred in yields of 0.0012% w/w. This compound was also the most irritant substance isolated and exhibited an I.D.50 of 0.038microgram, and is accordingly considered to be responsible for the major part of the toxicity of E. helioscopia. A high molecular weight aliphatic ester, 12-deoxyphorbol-13-dodecdienoate-20-acetate, was also obtained in low yields. This compound exhibited an I.D.50 of 0.12microgram. The final two esters obtained from the toxic fraction of the plant were the low molecular weight homologues, 12-deoxyphorbol-13-[2-methyl-cis-2-butenoate]-20-acetate and 12-deoxyphorbol-13-[2-methyl-cis-2-butenoate]. These compounds exhibited I.D.50 of 3.09 and 0.72 microgram, respectively and were the least irritant of the series of compounds isolated.