Irritant principles of the spurge family (Euphorbiaceae). XIII. Oligocyclic and macrocyclic diterpene esters from latices of some Euphorbia species utilized as source plants of honey.

The latices of the three South African species Euphorbia ledienii, Euphorbia coerulescens, and Euphorbia triangularis, belonging to a group of cactiform Euphorbias locally called "Noors," were shown to contain four 12-mono- and three 13,20-diesters of the tetracyclic tigliane type parent alcohol 12-deoxyphorbol [1]. In addition, two 13,16-di- and two 13,16,20-triesters of the related 12-deoxy-16-hydroxyphorbol [9] were obtained. Ester groups in 1 and 9 are made up of acetic, isobutyric, tiglic, angelic, and 2-methylbutyric acid; their positions in the parent alcohols were identified. The free parent alcohols were not detected in the latices. On the mouse ear all esters isolated showed moderate irritant activity as compared to the tigliane-type standard TPA. In addition to the oligocyclics listed above, the latex of E. ledienii also yielded five esters of the macrocylic, lathyrane type parent alcohol ingol [14]. In the two triesters and three teraesters the ester groups were made up of acetic, tiglic, and 2-methylbutyric acid (positions in 14 unidentified). None of the ingol esters showed irritant activity.