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The preparation of the daphnane prototype polyfunctional diterpene resiniferonol from resiniferatoxin (1) contained in latex from Euphorbia unispina or E. poisonii was modified to convert in an `early’ fraction of the acetone extract the extremely irritant 1 to the much less irritant 9,13,14-ortho(phenylacetate) 2 by transesterification. 2 was obtained in good yields and can be handled conveniently to prepare resiniferonol as reported previously. By esterification of resiniferonol with homologous straight chain aliphatic acids from C 2  to C 18  resiniferonol-14,20-diacylates were prepared. Treatment of the diacylates with perchloric acid/methanol yielded by intramolecular formation of the orthoester function the corresponding 9,13,14-orthoester-20-acylates. They were cleaved selectively by base catalysed transesterification to obtain the resiniferonol-9,13,14-orthoacetate (3), -hexanoate (4), -decanoate (5), -tetradecanoate (6) and -octadecanoate (7). On the mouse ear, unexpectedly they exhibit only weak irritant activity and on the mouse back skin practically no tumor promoting activity.

zeitschrift für naturforschung b

On the Chemistry of Resiniferonol. I. Preparation of Resiniferonol, Synthesis of Homologous Aliphatic Resiniferonol-9,13,14-orthoesters and Some of their Bioactivities