Since the discovery of the antibacterial penicillium more than 60 years ago, there has been a great deal of interest in finding new natural or synthetic compounds with antibacterial activity. The first quinolones used as antibacterial agents were nalidixic (1) and oxolinic (2) acids (Scheme. 1). However, these quinolones showed activity only against gram-negative microorganisms 1, 2 and 3. Subsequent structural modifications on these quinolones have led to new ...