AFN-1252 (API-1252) tosylate is an orally active and selective inhibitor of FabI , an essential enzyme in fatty acid biosynthesis in Staphylococcus spp. AFN-1252 tosylate exhibits exquisite and highly selective activity against Staphylococcus spp. AFN-1252 tosylate exhibits typical MIC 90 values of ?0.015 μg/ml against diverse clinical isolates of S. aureus. AFN-1252 tosylate is efficacious in a mouse model of septicemia providing 100% protection from an otherwise lethal peritoneal infection of S. aureus Smith.