The Structure of a Human Metabolite of Pholcodine

Abstract

The structure of a metabolite of pholcodine produced by humans is shown, by spectroscopic and synthetic data, to be a morpholin-3-one (amide) derivative rather than the alternative morpholin-2-one ( lactone ) isomer. Acylation of diethanolamine leads to an N,O- diacyl product even when only 1 equiv. of acylating agent is used. A mechanism is proposed to account for this observation. The appropriately substituted diacyl product can be cyclized to give a morpholin-3-one derivative which can be coupled to morphine by using caesium carbonate to give the metabolite. Suitable morpholin-2-one systems were coupled with morphine in basic conditions to give the alternative metabolite structure whose lactone group hydrolysed on standing to form a hydroxy acid derivative.