Oxanosine, a novel nucleoside from actinomycetes

Oxanosine, a novel nucleoside, has been isolated from the culture filtrate of a strain of Streptomyces. The structure was determined to be 5-amino-3-beta-D-ribofuranosyl-3H-imidazo [4,5-d] [1,3]oxazin-7-one by X-ray crystallographic analysis and chemical studies. Oxanosine showed weak antibacterial activity on peptone agar; for example, Escherichia coli K-12 (MIC 12.5 mcg/ml). The antibacterial activity was antagonized by addition of guanine, guanosine and 5'-guanylic acid. Oxanosine inhibited the growth of HeLa cells in vitro (IC50 32 mcg/ml) and suppressed the growth of L-1210 leukemia in mice. The primary action of oxanosine appears to be inhibition of GMP-synthetase. Intravenous injection of 4 mg of oxanosine to mice does not show any toxic sign.