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.