Biosynthesis of the furoquinoline alkaloids, skimmianine, evoxine, and choisyine: mechanism of formation of the furan ring. The timing of aromatic hydroxylation and of methylation

Abstract

Tracer feeding experiments with Choisya ternata using doubly labelled precursors confirm that dictamnine (2a) is converted into skimmianine (2b), and show that the 4-methoxy-group of a 3-prenylquinolone precursor (1b) is retained in skimmianine; in the formation of the furan ring from platydesmine (3), a carbonyl derivative is not an intermediate; a similar biosynthetic route applies to the 7,8-dioxygenated quinoline, evoxine (4) and to the 6,7-derivative, choisyine (5).