The Succulent Euphorbias of Nigeria. III. Structure and Potency of the Aromatic Ester Diterpenes of Euphorbia Poissonii Pax

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Abstract
The latex of E. poissonii was found to contain irritant aromatic diterpene esters based upon resiniferonol, 12-deoxy-16-hydroxy-phorbol and 12-deoxyphorbol. Four resiniferonol esters, 9,13,14-o-phenylacetyl-resiniferonol-20-0-[p-hydroxy-phenylacetate]; 9,13,14-o-phenylacetyl-resiniferonol-20-0-[m-methoxy-m''-hydroxy-phenylacetate]; 9,13,14-o-phenylacetyl-resiniferonol-20-0-acetate and resiniferonol-14-0-phenylacetate-20-0-[m-methoxy-m''-hydroxyphenylacetate], were identified. Two further esters were identified as 12-deoxy-16-0-[2-methylbutyroyl]-phorbol-13-0-phenylacetate-20-0-acetate and 12-deoxy-16-0-[2-methylbutyroyl]-phorbol-13-0-phenylacetate. These compounds represent the first aromatic esters of this parent diterpene to be obtained from natural sources. The third group of compounds were identified as 12-deoxyphorbol-13-0-[p-hydroxyphenylacetate]-20-0-acetate; 12-deoxyphorbol-13-0-[p-acetoxyphenylacetate]-20-0-acetate; 12-deoxyphorbol-13-0-phenylacetate-20-0-acetate and 12-deoxyphorbol-13-0-phenylacetate. The irritant potency of the 10 pure compounds was obtained using a mouse ear method for assessment of the irritant dose 50%.