Abstract
For the search of the more active antimicrobial compounds than the 2, 6-disubstituted derivatives, 3, 6-disubstituted 2, 3, 6, 9-tetrahydro-2, 9-dioxothiazolo [5, 4-f] quinoline-8-carboxylic acid (1, 3, 7, 8, 11, 20, 21, and 22) were synthesized from the 2-oxo-6-substituted thiazolo [5, 4-f] quinoline derivatives (2, 17, or 18). Thermal rearrangement of the 2-methylthio derivative (23) gave the 2-thioxo-3-methyl derivative (24), which was converted into the 2-oxo-3-methyl derivative (26) by reaction with mercuric acetate. The 2-ethoxy derivative (27) was also thermally rearranged to give the 2-oxo-3-ethyl derivative (8b). The 3, 6-disubstituted compounds obtained in this work showed the stronger activities against gram-negative and gram-positive bacteria in vitro than nalidixic acid and the 2, 6-disubstituted derivatives prepared in the previous work. 6-Ethyl-2, 3, 6, 9-tetrahydro-3-methyl-9-oxothiazolo [5, 4-f] quinoline-8-carboxylic acid (8a) exhibited the strongest activities among these compounds against many gram-negative bacteria including E. coli resistant to nalidixic acid and Ps. aeruginosa, and against some gram-positive bacteria.
