Abstract
Antimicrobial activities of 98 thiazoloquinolinecarboxylic acids were determined in vitro. Activities were classified into four groups, +++, ++, +, -, based on the average bacteriostatic index calculated by the equation, log2 [100/MIC (μg/ml)]. In the 2, 6-disubstituted derivatives, 2-alkoxy compounds were active only against Gram-positive bacteria, while 2-HO, MeO2S and NC derivatives were active only against Gram-negative bacteria. 2-Amino and 2-carbamoyl compounds had no activities. In the 3, 6-dialkyl-2-oxo derivatives, the most effective alkyl substituent was Me or Et group. Replacement of 2-oxo group by thioxo, imino or hydrazino group resulted in lowering of the activities. The maximum activity of 3-N-alkyl compounds existed in the Me group against both Gram-positive and -negative bacteria, while the corresponding 2-O-alkyl derivatives became stronger against Gram-positive bacteria, but weaker against Gram-negative bacteria with the increase in the length of methylene chain. 6-Ethyl-2, 3, 6, 9-tetrahydro-3-methyl-2, 9-dioxothiazolo [5, 4-f] quinoline-8-carboxylic acid was found to have the highest activities against Gram-positive and -negative bacteria including Escherichia coli resistant to nalidixic acid and Pseudomonas aeruginosa.
