Biosynthesis of aromatic isoprenoids. Part III. Mechanism of formation of the furan ring and origin of the 4-methoxy-group in the biosynthesis of furoquinoline alkaloids

Abstract

The incorporation of a 3-(3-methylbut-2-enyl)-2-quinolone doubly labelled at the benzylic methylene group into the furoquinoline alkaloids, skimmianine (5a), evoxine (5b), and choisyine (6) in Choisya ternata resulted in retention of half the tritium label, showing that a carbonyl derivative is not an intermediate in the formation of a furan ring from platydesmine (4). Feeding experiments also establish that the 4-methoxy-group of a 3-(3-methylbut-2-enyl)quinolone precursor is retained in skimmianine.