A potent and selective bacterial leucyl-tRNA synthetase inhibitor; active against strains of Enterobacteriaceae (MIC50/90 = 0.5/1 μg/ml) and the non-fermentative Gram-negative clinical isolates P. aeruginosa, A. baumannii, S. maltophilia, and B. cepacid (MIC50/90s = 4/8, 4/8, 2/4, and 8/32 μg/ml, respectively); bacterial resistance led to termination of a Phase II clinical trial,