Studies on the biosynthesis of violacein. Part 9.1 Green pigments possessing tetraindole and dipyrromethene moieties, chromoviridans and deoxychromoviridans, produced by a cell-free extract of Chromobacterium violaceum and their biosynthetic origins

Abstract

Novel green-coloured pigments, 5 and 6, are reported, which are concomitantly produced under a cell-free system together with the pigments of violaceins 1, 2 and proviolaceins 3, 4. The metabolites 5 and 6 have been named deoxychromoviridans and chromoviridans, respectively. The structures of 5 and 6 were established by analyses of the FABMS and various types of 2D-NMR spectra as 3-[2-{(Z)-[3,5-di(1H-indol-3-yl)-1H-pyrrol-2-yl]methylidene}-5-(1H-indol-3-yl)-2H-pyrrol-3-yl]-1H-indole and 3-[2-{(Z)-[3,5-di(1H-indol-3-yl)-1H-pyrrol-2-yl]methylidene}-3(1H-indol-3-yl)-2H-pyrrol-5-yl]-1H-indol-5-ol, respectively, and are closely related to those of violaceins 1, 2 and proviolaceins 3, 4, although they have an extra C₁ unit at the dipyrromethene moiety and were not oxygenated at any position. The C₁ unit of the dipyrromethene moiety was demonstrated to come from serine by feeding labelled [3-¹³C]serine, indicating that serine hydroxymethyltransferase and methylenetetrahydrofolate are responsible for the biosyntheses. The green pigments also have metal chelation capability with iron, copper, zinc and cobalt ions.