Novel antibiotics SF2738A, B and C, and their analogs produced by Streptomyces sp

Three new antibiotics SF2738A, B and C, and their analogs were isolated from the culture broth of Streptomyces sp. The antibiotics are active against Gram-positive bacteria, Gram-negative bacteria and fungi, and exhibited cytotoxic activity against P388 murine leukemia cells with IC50 values of 0.08, 0.25 and 7.5 micrograms/ml, respectively. Their structures were determined by spectral analyses and chemical conversion. Especially, the structure of SF2738A was confirmed to be (E)-((4-methoxy-5-methylthio-2-(2-pyridyl)pyridin-6-yl)methylene)azan ol by X-ray crystallographic analysis.