Transformation of streptonigrin into streptonigrone; synthesis and biological evaluation of antibiotics streptonigrin and streptonigrone alkyl ethers.

A method of synthesis of antibiotic streptonigrin 8'-O-alkyl ethers by alkylation of streptonigrin diphenylmethyl ester and consequent deprotection of carboxylic group with CF3COOH is developed. An attempt to deblock carboxylic group of 8'-O-methylstreptonigrin diphenylmethyl ester by hydrogenation over Pd produced 8'-O-methylstreptonigrone. Similarly streptonigrin was transformed into streptonigrone over Pd-black in H2 stream. Methylation of streptonigrone afforded 5',5'-N-dimethyl-2',8'-O-dimethylstreptonigrone and 1',5',5'-tri-N-trimethyl-8'-O-methylstreptonigrone. Alkyl streptonigrin ethers demonstrated lower antibacterial activity in vitro than the parent antibiotic.