The formation of corydaline and related alkaloids in Corydalis cava in vivo and in vitro

The biosynthesis of corydaline and thalictricavine has been investigated by application of [8-3H]-labelled palmatine and berberine to Corydalis cava bulb tissue. In both cases, high incorporation into the respective (14R,13S)corydaline and -thalictricavine was observed. (S)-[14-3H, 8-14C]Scoulerine was also transferred into corydaline with all of the tritium being lost, indicating that a redox reaction had taken place in the transition of the (14S) to the (14R) product. A partly enriched protein fraction catalyzed the reduction of both protoberberine precursors to the 7,8-dihydro intermediate, which was subsequently methylated at C-13 at the expense of S-adenosylmethionine (SAM) and reduced at C-14 by a B-type reaction with NADPH as reductant. The identity of the product was unequivocally established by NMR, MS, and CD measurements. This biosynthetic route is in full agreement with previously published predictions based on in vivo experiments.