Phenol oxidation and biosynthesis. Part XVIII. The structure and biosynthesis of Erythrina alkaloids

Abstract

The final details of the constitutions of the aromatic Erythrina alkaloids erysodine, erysovine, erysonine, erythratine, and erythramine have been elucidated by a combination of chemical and spectroscopic methods. Similarly the stereochemistry of erythratine has been determined. Erythratine and erythramine have the biogenetically preferred position for the ethylenic linkage.

An improved synthesis of bis-2-(3-hydroxy-4-methoxyphenyl)ethylamine has been developed both in active and radiochemically inactive form. Although this compound has usually been regarded as the precursor of the Erythrina alkaloids it is scarcely incorporated into the akaloids of Erythrina crista-galli. A new biogenetic precursor, N-norprotosinomenine, has been postulated as the parent of the Erythrina alkaloids and relatively good incorporations have been secured. The Erythrina alkaloids appear, therefore, to be in reality benzylisoquinoline alkaloids.

The new theory does not alter the final steps in the biosynthesis. Labelling and other experiments provide good support for the final stages of biosynthesis as previously postulated. A search for one of the presumed final intermediates, erythratinone, has revealed that it is a new Erythrina alkaloid and one of the major basic constituents of Erythrina crista-galli.