Polybenzoate und -acetate des Phorbols und Phorbol-3-ols und funktionelle Derivate der Allylgruppierung des Phorbols

Abstract

Base catalysed transesterification of phorbol-12,13,20-tribenzoate yields phorbol-12,13-dibenzoate. By base catalysed transesterification of phorbol-pentaacetate phorbol-9,12,13-triacetate is obtained. This can be re-acetylated to give phorbol-9,12,13,20-tetraacetate which is also obtained by treatment of phorbol-12,13,20-triacetate with acetic anhydride/p-toluene-sulfonic acid. Reduction of phorbol-12,13,20-triacetate with LiAlH4 yields phorbol-3-ol which reduces Fehling's and Tollen's reagent. Reduction of the 3-keto group alone can be accomplished with sodium borohydride. From all phorbol-esters investigated only in phorbol-pentaacetate an acetyl migration is observed during the sodium borohydride reduction leading to phorbol-3-ol-3,9,12,13,20-pentaacetate. By these findings those two tertiary hydroxyl groups of phorbol which are not acetylated with acetic anhydride/pyridine at room temperature were further characterized. Oxidation of phorbol-12,13-diacetate with activated manganese dioxide yields phorbol-20-al-12,13-diacetate. By evaluation of nmr-spectra of this aldehyde and of some of its derivatives as well as of the epoxide of phorbol-12,13-diacetate and of 6-oxo-7-hydroxy- and 6,7-diacetoxy-20-nor-phorbol-12,13-diacetate the sequence of C-atoms around the allylic alcohol group of phorbol is further characterized.