Tracer experiments show that the bisbenzylisoquinoline alkaloid, (S,R)-hayatidin (10) is stereospecifically biosynthesized in young Cissampelos pareira Linn plants by intermolecular oxidative coupling of (S)-(5)-and (R)-(3), N-methylcoclaurines whereas (R,R)-isochondrodendrine (14) and (R,R)-bebeerine (12) are formed in the plants by oxidative dimerization of (R)-N-methylcoclaurine (3). © 1987.