The present invention features rifamycin analogs that can be used as therapeutics for treating or preventing a variety of microbial infections. In one form, the analogs are acetylated at the 25-position, as is rifamycin. In another form, the analogs are deacetylated at the 25-position. In yet other forms, benzoxazinorifamycin, benzthiazinorifamycin, and benzdiazinorifamycin analogs are derivatized at various positions of the benzene ring, including 3'-hydroxy analogs, and/or various fused ring systems with the benzene ring at the 4',5' or 5',6' positions.