The effect of halide salts on the production of Gymnoascus reessii polyenylpyrroles

Addition of NaCl to the solid-phase fermentation of an Australian isolate of Gymnoascus reessii resulted in enhanced production of chloropolyenylpyrroles, while the addition of NaBr suppressed chloropolyenylpyrrole production in favor of bromo and dechloro analogues. Access to a wider selection of polyenylpyrroles provided scope for SAR comparisons on this rare class of cytotoxic natural products, with the bromo- and dechloropolyenylpyrroles displaying significantly reduced cytotoxicity. These results suggest that the chloro substituent is a critical element in the pharmacophore for this rare class of natural product.