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Schemes for the degradation of narcotine (111) are devised which allow unambiguous isolation of labelled atoms from the alkaloid isolated from Papaversomniferum plants fed with a variety of precursors, both singly and multiplylabelled. 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). 0-, 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.

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