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.
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Zeitschrift für Naturforschung B is an international scientific journal which publishes original papers, microreviews, and letters from all areas of inorganic chemistry, solid state chemistry, coordination chemistry, molecular chemistry, and organic chemistry.