Labelled precursors for biosynthetic studies on naphthylisoquinoline alkaloids

The isotope labelled monocyclic ketones 5 and 8, postulated precursors to the presumably acetogenic naphthylisoquinoline alkaloids, have been synthesized for biogenetic experiments to Ancistrocladaceae and Dioncophyllaceae plants. Key step of the preparation of 1-(2′-[carbonyl-14C]acetyl-3′,5′-dibenzyloxyphenyl)-2-propanone ([14C]-13) is the C-acetylation of the arylpropanone 10 with the mixed pivalic acetic anhydride ([14C]-11). The resulting pyrylium salt [14C]-12, which is stable and can be stored, is cleaved directly before the feeding experiment to give the diketone [14C]-13 and deprotected to give the free phenolic target molecule [14C]-5. This synthetic route is applicable also to the prepation of 1-(2′-[13C2]acetyl-3′-hydroxyphenyl)-2-propanone ([13C2]-5) for biosynthetic experiments with NMR analysis. For the preparation of the oxygen-poorer 13C-labelled diketone 1-(2′-[methyl-13C]acetyl-3′-hydroxyphenyl)-2-propanone ([13C]-8), an ‘indanone-route’ has been elaborated. © 1997 John Wiley & Sons, Ltd.