Antibacterial oxazolidinone analogues having a N-hydroxyacetyl-substituted seven-membered [1,2,5]triazepane or [1,2,5]oxadiazepane C-ring unit

► We synthesized oxazolidinone analogues bearing seven-membered heterocycle C-ring unit. ► Several compounds exhibited potent in vitro antibacterial activities. ► Compounds 21a and 21b showed high in vivo activity against MRSA. ► The above 21a and 21b also had promising safety profile.