LY-255262

The synthesis and biological evaluation of a series of pyrazolidinone-containing mono- and bicyclic compounds are described. The results of this investigation indicate that the [3.3.0] ring system bearing strongly electron-withdrawing groups in the 3-position provides the optimal arrangement for antibacterial activity. Two highly potent derivatives, LY193239 and LY255262, have been selected for further preclinical evaluation.