NOVEL AND POTENT GASTRIN AND BRAIN CHOLECYSTOKININ ANTAGONISTS FROM Streptomyces olivaceus: TAXONOMY, FERMENTATION, ISOLATION, CHEMICAL CONVERSIONS, AND PHYSICO-CHEMICAL AND BIOCHEMICAL PROPERTIES

The discovery and physico-chemical characterization of three novel and minor virginiamycin M1 analogs as potent gastrin antagonists from a culture of a strain of Streptomyces olivaceus are described. These analogs are L-156, 586, L-156, 587 and L-156, 588. They are, respectively, 15-dihydro-13, 14-anhydro-, 13, 14-anhydro- and 13-desoxy-analogs of virginiamycin M1. We also chemically converted virginiamycin M1 (via L-156, 587) to L-156, 586 and its unnatural epimer, L-156, 906. These analogs are competitive and selective antagonists of gastrin and brain cholecystokinin binding at nanomolar concentrations. These are the most potent gastrin/brain cholecystokinin antagonists from natural products. The same compounds showed poor Gram-positive antibiotic activity versus virginiamycin M1. Structurally related Gram-positive antibiotics, griseoviridin and madumycin I, were inactive in gastrin and brain cholecystokinin binding at up to 100 μM.