© Georg Thieme Verlag Stuttgart · New York
Cryptic and Free Skin Irritants of the Daphnane and Tigliane Types in Latex of Excoecaria agallocha 11 Part III in the series “Medicinal Plants of Euphorbiaceae Occurring and Utilized in Thailand”. For part II, see Ref. (1)
04 January 2007 (online)
In the extremely skin irritant and caustic latex of Excoecaria agallocha the major part of the polyfunctional diterpene esters (DTE) (group I) are aliphatic polyunsaturated 9,13,14-orthoesters of the daphnane-type parent alcohol 5β-hydroxyresiniferonol-6α,7α-epoxide, esterified simultaneously in their 20-positions with aliphatic saturated homologous n-carboxylic acids (even numbered, C22-C30). The minor part of DTE is composed of analogous structures of 5β,12β-dihydroxyresiniferonol-6α,7α-epoxide (group II) and of aliphatic 13-polyunsaturated, 20-saturated diesters of the tigliane-type parent alcohol 12-deoxyphorbol (group III). All three groups of DTE exhibit practically no irritant activity on the mouse ear. By alkaline transesterification of groups I-III, the corresponding highly irritant multicomponent mixtures of Excoecaria factors A (OH-20 deacylated) are released. They comprise a mixture of the known Excoecaria factors A1/A2/A3 and three mixtures of hitherto unknown Excoecaria factors A4/A5, A6/A7 and A8/A9. The groups I-III are typical structures of “cryptic irritants”. By an alternative, extremely mild separation procedure the highly irritant mixture A1/A2/A3 was obtained directly. It represents the “free” Excoecaria factors, the natural constituents of the latex responsible for its bioactivity.
Daphnane-type orthoesters - 12-deoxyphorbol esters - Euphorbiaceae - Excoecaria agallocha - skin irritants