A semisynthetic β-lactam antibiotic; active against clinical isolates of methicillin-susceptible S. aureus and penicillin-susceptible S. pneumoniae, as well as group A, group B, and viridans group streptococci in vitro (MIC90s = 0.06-2 μg/ml); less effective toward other bacteria (MIC90 = >16 μg/ml for S. epidermidis, S. haemolyticus, E. faecalis, E. faecium, MRSA, and penicillin-intermediate and -resistant S. pneumoniae); targets the bacterial cell wall; inhibits S. pneumoniae penicillin-binding proteins 1a, 1b, 2a, 2b, and 3 in vitro (IC50s = 0.17-1.75 μM); inhibits growth of S. aureus in a thigh model of infection in mice (ED50 = 45.19 mg/kg, s.c.)