Compounds of the current invention relate to rifamycin derivatives having antimicrobial activities, including activities against drug-resistant microorganisms. More specifically, compounds of the current invention relate to C-25 carbamate derivatives of rifamycin having another functional group or pharmacophore covalently attached to this position through a carbamate linkage. The resulting compounds exert their antimicrobial activity through a dual-function mechanism and therefore exhibit reduced frequency of resistance.