Pseudodeoxyviolacein, a New Red Pigment Produced by the Tryptophan Metabolism of Chromobacterium violaceum

Abstract

A novel tryptophan metabolite colored with reddish orange was isolated by addition of diethyl-dithiocarbamate to washed cells of Chromobacterium violaceum. The molecular formula was identical to that of deoxyviolacein. The chemical structure was found to be 5-(3-oxoindolylidene)-3-(indol-3-yl)-3-pyrroline-2-one by means of 2D NMR in exhaustive comparisons with the structure of deoxyviolacein. The novel metabolite was named pseudodeoxyviolacein. The five cross peaks in HMBC spectra and the conformation analysis in NOESY spectra were helpful in proposing the chemical structure of the novel metabolite. Electronic spectra calculated by using a CAChe system (ZINDO) showed that the maximal absorption of pseudodeoxyviolacein is shorter than that of dexoyviolacein, giving additional evidence for the structure of pseudodeoxyviolacein. The structure differs from that of deoxyviolacein only with regard to the oxygenation for two indole rings.