The biosynthesis of the alkaloids of stephania glabra (ROXB.) miers

Tracer experiments show that the tetrahydroprotoberberines stepholidine (14), corydalmine (d15), capaurine (19) and corynoxidine (20) are stereospecifically biosynthesized from (S)-reticuline (22) whereas the bisbenzylisoquinoline alkaloids cycleanine (52), N-desmethylcycleanine (51) and the proaporphine alkaloids. pronuciferine (27) and stepharine (26) are derived from (R)-N-methylcoclaurine in young Stephania glabra. The quaternary protoberberine alkaloids (40 to 44) of the plant are formed by dehydrogenation of the corresponding tetrahydroprotoberberines