Synthesis and biological activity of new quinoxaline antibiotics of echinomycin analogues

Novel quinoxaline antibiotics having the methylenedithioether bridge as an analogue of echinomycin have been synthesized by insertion of methylene moiety between –S–S– bond. The compound 1a shows remarkable cytotoxicities against human tumor various cell lines, and is active VRE (vancomycin-resistant enterococci) within MIC range 0.5–8 μg/mL. According to the eukaryotic or prokaryotic data, 1a might be a first analogue to replace echinomycin.