Biosynthesis of boldine (1,10-dimethoxy-6aα-aporphine-2,9-diol)
The incorporation of (±)-norprotosinomenine, (±)-nororientaline, (±)-nor-reticuline, and (±)-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 (+)-reticuline 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-group of (±)-reticuline showed that most, but not all, of the methoxy-activity was lost in conversion into boldine.