Quinolone antibacterials. 2. 6‐Substituted‐7‐(2‐thiazolyl and thiazolidinyl)quinolones

A series of 6-substituted-1-ethyl-1,4-dihydro-4-oxo-7-(2-thiazolyl- and thiazolidinyl)quinoline-3-carboxylic acids were synthesized. Substitution at the 6-position was H, F or Cl. The Hantzsch method was used for the preparation of the thiazolylquinolones. The thiazolidinylquinolones were synthesized by quaternization of the corresponding thiazolyl analogues, followed by reduction of the obtained thiazolium salts with sodium borohydride in aqueous solution. Antibacterial activity was tested in vitro. The compounds were inactive against Gram-negative bacteria but some of them showed good activity against Gram-positive bacteria and mycobacteria. This activity pattern is rarely found among the quinolone antibacterials.