Studies of enzyme-mediated reactions. Part V. Synthesis of (13S)- and (13R)-[13-3H1]scoulerine from stereospecifically labelled (R)- and (S)-[α3H1]benzyl alcohols; stereochemistry of enzymic reactions at saturated benzylic carbon

Abstract

A synthesis of (14RS)-scoulerine [as (2)] has been developed which allows stereospecific labelling with deuterium or tritium at C-13; (14RS)-coreximine (45) is a valuable second product from the synthesis. The configurational purity of the labelled scoulerine was determined by degradation of a suitable intermediate, in the 2H series to monodeuteriosuccinic acid, and in the 3H-series to [3H]malic acid for configurational assay by fumarase.Incorporation experiments with (13R)- and (13S)-[13-3H1]scoulerine have proved that the biosynthesis of both narcotine (6) and chelidonine (7) involves stereospecific removal of the pro-S hydrogen atom from the saturated benzylic carbon, C-13 of scoulerine (2). The mechanistic implications of these findings are considered.