Abstract: Compound of formula (I) or salts thereof wherein R.sup.1 is hydrogen, methoxy or formamido; R.sup.2 is an acyl group; CO.sub.2 R.sup.3 is a carboxy group or a carboxylate anion, or R.sup.3 is a readily removable carboxy protecting group or a pharmaceutically acceptable salt-forming group or in vivo hydrolysable ester group; R.sup.4 represents hydrogen or up to four substituents; X is S, SO, SO.sub.2 or CH.sub.2 ; Y is O, S, SO or SO.sub.2 ; n is 0 or 1; m is 1 or 2; and wherein in the (a) ring system the dotted line indicates that one pair of adjacent ring carbon atoms is joined by a C.dbd.C double bond. These compounds have antibacterial activity.

Abstract: .beta.-lactam antibiotics of formula (I) or a salt thereof, wherein R.sup.1 is hydrogen, methoxy of formamido; R.sup.2 is an acyl group, in particular that of an antibacterially active cephalosporin; CO.sub.2 R.sup.3 is a carboxy group or a carboxylate anion, or R.sup.3 is a readily removable carboxy protecting group (such as a pharmaceutically acceptable in vivo hydrolysable ester group); R.sup.4 represents up to four substituents selected from alkyl, alkenyl, alkynyl, alkoxy, hydroxy, halogen, amino, alkylamino, acylamino, dialkylamino, CO.sub.2 R, CONR.sub.2, SO.sub.2 NR.sub.2 (where R is hydrogen or C.sub.1-6 alkyl), aryl and heterocyclyl, which may be the same or different and wherein any R.sup.4 alkyl substituent is optionally substituted by any other R.sup.4 substituent; X is S, SO, SO.sub.2, O or CH.sub.2 ; Y is S, SO or SO.sub.2 ; and m is 1 or 2, useful in the treatment of bacterial infections in humans and animals.

Abstract: Compounds of the formula: ##STR1## wherein R.sup.1 is hydrogen, methoxy or formamido;R.sup.2 is an acyl group, in particular that of an antibacterially active cephalosporin;CO.sub.2 R.sup.3 is a carboxy group or a carboxylate anion, or R.sup.3 is a readily removable carboxy promoting group or a pharmaceutically acceptable salt-forming group or in vivo hydrolysable ester group;R.sup.4 represents hydrogen or up to four substituents, which my be present on any of the carbon atoms in the ring system shown, selected from alkyl, alkenyl, alkynyl, alkoxy, hydroxy, halogen, amino, alkylamino, acylamino, dialkylamino, CO.sub.2 R, CONR.sub.2, SO.sub.2 NR.sub.2 where R is hydrogen or alkyl, aryl and heterocyclyl, which may be the same or different and wherein any R.sup.4 aryl substituent is optionally substituted by one or more substituents selected from the list from which R.sup.4 is selectedY is O, S, SO or SO.sub.2 ; n is 0 or 1; and m is 1 or 2;for use in the treatment of bacterial infections in humans and animals.

Abstract: .beta.-Lactam compounds of the formula (Ia) including pharmaceutically acceptable salts and in vivo hydrolysable esters, processes for their preparation and their use as antibiotics: ##STR1## wherein R.sup.1 is hydrogen, methoxy or formamido;R.sup.2 is an acyl group, in particular that of an antibacterially active cephalosporin;CO.sub.2 R.sup.6 is a carboxy group or a carboxylate anion;R.sup.3 is a Y-lactone ring optionally containing an endocyclic double bond, which ring is optionally substituted at any carbon atom by alkyl, dialkylamino, alkoxy, hydroxy, halogen or aryl, which in the case of more than one substituent may be the same or different, or is optionally di-substituted at two adjacent carbon atoms, which are available for substitution, to form an aromatic fused bicyclic system; and X is S, SO, SO.sub.2, O or CH.sub.2.

Abstract: .beta.-Lactam antibiotics of the formula (Ia) or a pharmaceutically acceptable salt or pharmaceutically acceptable in vivo hydrolysable ester thereof are disclosed: ##STR1## wherein R.sup.1 is hydrogen, methoxy or formamido; R.sup.2 is a acyl group, in particular that of an antibacterially active cephalosporin; CO.sub.2 R.sup.6 is carboxy group or a carboxylate anion; R.sup.4 is a butenolide or butanolide ring, optionally substituted by one or two alkyl, dialkylamino, alkoxy, hydroxy or aryl groups, which may be the same or different, or, wherein two adjacent carbon atoms which are available for substitution define the common bond of an aromatic fused bicyclic system; X is S, SO, SO.sub.2, O or CH.sub.2 ; and the dashed line adjacent to R.sup.4 represents an optional double bond. Processes for the preparation of compounds together with intermediates for use therein are disclosed.