Studies on the Blue Pigments Produced from Genipin and Methylamine. II. On the Formation Mechanisms of Brownish-Red Intermediates Leading to the Blue Pigment Formation.

Abstract

The mechanisms of the formation of brownish-red pigments having a 2-methyl-4-carbomethoxy-2-pyrindine nucleus as a basic skeleton by reaction of genipin with methylamine under an atmosphere of inert gas are discussed based on the isolation of 5, 6-dihydro-2-methyl-4-carbomethoxy-8-hydroxymethyl-2-pyrindine as a precursor and on comparisons of the results obtained from the reactions of genipin congeners and methylamine. The origin of the extra methyl group at C-6 in the structures of some of the brownish-red pigments was clarified to be the carbon atom of the hydroxymethyl group at C-8 of genipin by using deuterium-labelled genipin.