Biosynthesis of oxyacanthine

Abstract

The incorporation of (±)-norcoclaurine, (±)-coclaurine, (±)-N-methylcoclaurine, didehydro-N-methylco-claurinium iodide, (+)-(S)-N-methylcoclaurine and (–)-(R)-N-methylcoclaurine into oxyacanthine in Cocculus laurifolius DC has been studied and specific utilization of (±)-N-methylcoclaurine, (+)-(S)-N-methylcoclaurine, (–)-(R)-N-methylcoclaurine, and didehydro-N-methylcoclaurinium iodide demonstrated. The evidence supports intermolecular oxidative coupling of (+)-(S)-N-methylcoclaurine and (–)-(R)-N-methylcoclaurine to give oxyacanthine. A double labelling experiment with (±)-[1-³H,N-¹⁴CH₃]-N-methylcoclaurine demonstrated that the hydrogen atom at the asymmetric centre in the 1-benzylisoquinoline precursor is retained in the bioconversion into oxyacanthine.