The reaction of 7‐chloro‐1‐methylpyridazino[3,4‐b]quinoxalin‐4(1H)‐ones 3a‐5a with sodium methylthiolate gave 1‐methyl‐7‐methylsulfanylpyridazino[3,4‐b]quinoxalin‐4(1H)‐ones 8a‐c, whose reaction with m‐chloroperbenzoic acid afforded the 7‐methanesulfonyl‐1‐methylpyridazino[3,4‐b]‐quinoxalin‐4(1H)‐ones 9a‐c, respectively. The above substituent change at the 7‐position resulted in the activity alteration to microorganisms.

Pyrazine derivatives R 0550Quinolone Analogues. Part 9. Synthesis of 7-Methylsulfanyl-and 7-Methanesulfonylpyridazino[3,4-b]quinoxalin-4(1H)-ones. -Title compounds (III) and (IV) are synthesized and evaluated for their antimicrobial effectss. The starting materials (I) exhibit antifungal activity, which is reduced considerably in substitution products (III) and (IV). However, derivatives (IIIa) and (IVa) show improved antibacterial activity to a few kinds of bacteria; (IIIb), (IVa) and (IVc) possess algicidal activity. -(KURASAWA*, Y.; NAKAMURA, M.; ASHIDA, H.; MASUDA, M.; KAJI, E.; OKAMOTO, Y.; KIM, H. S.; J. Heterocycl. Chem. 44 (2007) 6, 1231-1234; Sch. Pharm. Sci., Kitasato Univ., Minato, Tokyo 108, Japan; Eng.) -H. Toeppel 11-157