MEDICINAL-PLANTS OF EUPHORBIACEAE OCCURRING AND UTILIZED IN THAILAND .5. SKIN IRRITANTS OF THE DAPHNANE AND TIGLIANE TYPE IN LATEX OF EXCOECARIA BICOLOR AND THE UTEROTONIC ACTIVITY OF THE LEAVES OF THE TREE

From latex of Excoecaria bicolor (Euphorbiaceae) four TLC-homogeneous fractions highly enriched in diterpene esters were obtained (F1-F4). F raction F3 by NMR was found to be a mixture of 9,13,14-orthoester-20-e sters (1a) of 5 beta-hydroxyresiniferonol-6 alpha,7 alpha-epoxide (1). Alkaline transesterification yielded from la a mixture of 5 beta-hydr oxyresiniferonol-6 alpha, 7 alpha-epoxide-9,13-14-orthoesters (1f) car rying unsaturated orthoester groups as a TLC-homogeneous material (fin al isolation of Excoecaria factors B1/B2, B3 and B4). The transesterif ication mixture also contained, according to CC-MS, methyl n-carboxyla tes corresponding to the even numbered C-22-C-39 acids from 20-positio ns in 1a. Fraction F4 by NMR contained molecular species (2a) structur ally closely related to 1a, carrying 5 beta, 12 beta-dihydroxyresinife ronol-6 alpha,7 alpha-epoxide (2) as the parent alcohol. From 2a, by a lkaline transesterification, a two-component mixture of Excoecaria fac tors B5/B6, i.e. 5 beta,12 beta-dihydroxyresiniferonol-6 alpha,7 alpha -epoxide-9, 13, -hexadecatrienoate)/-(2,4,6,8-hexadecatetraenoate) (2b /2c) was obtained. CC-MS of the transesterification mixture revealed m ethyl n-carboxylates corresponding to even numbered C-16-C-30 acids fr om 20-positions in 2a (omitting C-18 and C-20). Fractions F1 and F2 by alkaline transesterifications yielded 12-deoxyphorbol (3) and its 13- (3,5-tetradecadienoate) 3b (Excoecaria factor B7). Moreover 4,12-dideo xy(4 alpha)phorbol (4), its 13-(3,5-tetradecadienoate) 4b and the natu ral 4-epimer of 4b 4,12-dideoxyphorbol-13-(3,5-tetradecadienoate) (5a) (new Excoecaria factor B8) were obtained. CC-MS of the transesterific ation mixtures revealed mainly methyl n-carboxylates corresponding to even numbered C-16-C-30 acids, Thus the latex and the fractions F1 and F2 contain 13,20-diesters of the parent alcohols 12-deoxyphorbol (3) and 4,12-dideoxyphorbol (5). 4,12-dideoxy(4 alpha)phorbol (4) and its derivatives may be considered artifacts from alkaline epimerization of 5. The daphnane type Excoecaria Factors B1-B6 are structurally very c losely related to diterpenes such as yuanhuacine occurring in certain Daphne and Wikstroemia species, Daphnane type esters of this kind are currently used routinely in China for fertility regulation. Similarly, daphnane and tigliane type Excoecaria factors present in the latex of E. bicolor may be responsible for the uterotonic activity of its leav es utilized in Thai herbal medicine.