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The incorporation of (k) -norprotosinomenine, (*) -nororientalhe, (i) -nor-reticuline, and (i) -reticuline into boldine in Litsea glutinosa has been studied, and the specific utilization of the (*) -reticuline demonstrated. The evidence supports the direct oxidative coupling of (+)-reticdine to give isoboldine, which in turn is shown to be a specific precursor of boldine. The plants also converted norboldine into boldine. Double labelling experiments involving the methoxy-groupof (f) -reticuline showed that most, but not all, of the methoxy-activity was lost in conversion into boldine. BOLDINE (l), the choleretic principle of Peumzls boldzlsMolina, could be formed in nature from suitable l-benzyltetrahydroisoquinoline precursors through various biosynthetic routes. Direct oxidative coupling of reticu-line2 (8) could give rise to the boldine; alternatively oxidative coupling of orientaline (10) and protosinomenine * (12) involving the dienones (15) and ( 16) , respectively, as intermediates, would furnish the required aporphine system by dienone-phenol rearrangement. We now report the details of studies on these and some other aspects of boldine biosynthesis.(&)-Tyrosine was initially fed to young shoots of Litsea glutimsa (Lauraceae), and it was found that the plants were actively biosynthesizing boldine. In subsequent experiments, labelled hypothetical precursors were fed to young L. glutinosa plants. The results of several feedings are recorded in the Table . Feeding (&) -tyrosine Expt.

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