In order to investigate the origin of the loop-type diureticactivity of M17055 (1), several variants (3-9) were designed and synthesized by modifying the quinolinone skeleton, and their diureticactivities were compared with the lead 1 and furosemide in dogs. It was found that the negative charge distribution pattern afforded by the dispositional arrangement of the 4-oxime-O-sulfonic acid and 1-N-acyl