Alkaloid biosynthesis. Part XII. The biosynthesis of narcotine

Abstract

Schemes for the degradation of narcotine (III) are devised which allow unambiguous isolation of labelled atoms from the alkaloid isolated from Papaver somniferum plants fed with a variety of precursors, both singly and multiply-labelled. It is shown in this way that the biosynthesis involves combination of two Ar–C–C units, derivable in the living plant from tyrosine, to generate norlaudanosoline (VII). O-, and N-Methylation from the S-methyl group of methionine then yields reticuline [as (X)], the (+)-isomer of which (X) undergoes oxidative ring-closure to yield (–)-scoulerine (XLII). Further oxidative attack at positions 1, 8, and 13 are then involved in the final steps leading to narcotine. The results from ³H, ¹⁴C-labelling experiments are in agreement with stereospecific attack at position 13.

The synthesis and resolution of labelled 1-benzylisoquinolines and scoulerine are described.