Diaryldiamines are a new class of antibacterial agents that inhibit methionyl t-RNA synthetase (MetRS). These inhibitors prevent protein synthesis and arrest the growth of bacteria cells. The diaryldiamines are particularly potent agents against a wide spectrum of Gram+ organisms. This presentation will focus on our discovery of a new diaryldiamine, REP3123, with particularly potent activity against Clostridium difficile. This anaerobe if present in the lower GI leads to a particularly debilitating clinical condition labeled Clostridium difficile associated disease (CDAD).