Abstract: | A compound of structural Formula I: ##STR1## or pharmaceutically acceptable salts thereof wherein: X is O, S, SO, SO.sub.2, SNR.sup.10 or S(O)NR.sup.10 ; R is (a) hydrogen, (b) C.sub.1 -C.sub.8 alkyl optionally substituted with one or more of the following: F, Cl, hydroxy, C.sub.1 -C.sub.8 alkoxy, C.sub.1 -C.sub.8 acyloxy or --O--CH.sub.2 --Ph, (c) C.sub.3 -C.sub.6 cycloalkyl, (d) amino, (e) C.sub.1 -C.sub.8 alkylamino, (f) C.sub.1 -C.sub.8 dialkylamino or (g) C.sub.1 -C.sub.8 alkoxy; R.sup.1 is H, except when X is O then R.sup.1 can be H, CH.sub.3, CN, CO.sub.2 H, CO.sub.2 R or (CH.sub.2).sub.m R.sup.11 (m is 1 or 2); R.sup.2 is independently H, F or Cl; R.sup.3 is H except when X is O and R.sup.1 is CH.sub.3 then R.sup.3 can be H or CH.sub.3 ; R.sup.10 is independently H, C.sub.1 -C.sub.4 alkyl (optionally substituted with chloro, fluoro, hydroxy, C.sub.1 -C.sub.8 alkoxy, amino, C.sub.1 -C.sub.8 alkylamino, or C.sub.1 -C.sub.8 dialkylamino) or p-toluenesulfonyl; R.sup.11 is hydrogen, OH, OR, OCOR, NH.sub.2, NHCOR or N(R.sup.10).sub.2 ; and n is 0, 1 or 2. The oxazine and thiazine oxazolidinone derivatives are useful antimicrobial agents, effective against a number of human and veterinary pathogens, including gram-positive aerobic bacteria such as multiply-resistant staphylococci, streptococci and enterococci as well as anaerobic organisms such as Bacteroides spp. and Clostridia spp. species, and acid-fast organisms such as Mycobacterium tuberculosis, Mycobacterium avium and Mycobacterium spp. |