| abstract |
β-Lactam antibiotics of formula (I) or a salt thereof, wherein R 1 is hydrogen, methoxy or formamido; R 2 is an acy group; CO 2 R 3 is a carboxy group or a carboxylate anion, or R 3 is a readily removable carboxy protecting group; R 4 represents up to four substituents; X is S, SO, SO 2 , O or CH 2 ; m is 1 or 2; and n is 0, useful in the treatment of bacterial infec ##STR1## |