LABELED PRECURSORS FOR BIOSYNTHETIC-STUDIES ON NAPHTHYLISOQUINOLINE ALKALOIDS

The isotope labelled monocyclic ketones 5 and 8, postulated precursors to the presumably acetogenic naphthylisoquinoline alkaloids, have bee n synthesized for biogenetic experiments to Ancistrocladaceae and Dion cophyllacene plants. Key step of the preparation of l-C-14]acetyl-3',5 '-dibenzyloxyphenyl)-2-propanone ([C-14]-13) is the C-acetylation of t he arylpropanone 10 with the mixed pivalic acetic anhydride ([C-14]-11 ). The resulting pyrylium salt [C-14]-13, which is stable and can be s tored, is cleaved directly before the feeding experiment to give the d iketone [C-14]-13 and deprotected to give the free phenolic target mol ecule [C-14]-5. This synthetic route is applicable also to the prepati on of -(2'-[C-13(2)]acetyl-3'-hydroxyphenyl)-2-propanone ([C-13(2)]-5) for biosynthetic experiments with NMR analysis. For the preparation o f the oxygen-poorer C-13-labelled diketone -[methyl-C-13]acetyl-3'-hyd roxyphenyl)-2-propanone ([C-13]-8), an 'indanone-route' has been elabo rated.