Structures of grixazone A and B, A-factor-dependent yellow pigments produced under phosphate depletion by Streptomyces griseus.

A-factor (2-isocapryloyl-3R-hydroxymethyl-gamma-butyrolactone) acts as a microbial hormone that induces morphological development and secondary metabolism in Streptomyces griseus. A diffusible yellow pigment is produced by S. griseus in an A-factor-dependent manner under phosphate depletion. Detailed analysis of the pigment production by S. griseus cultivated in minimal liquid medium containing different concentrations of phosphate showed that the pigment was actively produced in the presence of low concentrations of phosphate and the production of the pigment was completely repressed in the presence of 2.5 mM KH2PO4. HPLC analysis of the culture supernatant showed that the pigment consisted of two major, structurally related compounds and they were produced at different ratios depending on the concentration of phosphate in the medium. The structures of the two major compounds, designated as grixazone A and B, were determined by spectroscopic analyses as 1-[[2-(acetylamino)-2-carboxyethyl]thio]-2-amino-3-oxo-8-formyl-3H-phenoxiazine and 1-[[2-(acetylamino)-2-carboxyethyl]thio]-2-amino-3-oxo-8-carboxyl-3H-phenoxiazine, respectively. Grixazone A was a novel compound, although grixazone B was reported in a patent as a parasiticide produced by Streptomyces sp. DSM3813.