Alphalosporins and 1-carba-1-dethia cephalosporins

A compound of formula (I) or a salt thereof:

• ##STR20## wherein:
• R.sup.1 is hydrogen, methoxy or formamido;
• R.sup.2 is acyl groups of the formulae ##STR21## wherein p is 0, 1 or 2;
• m is 0, 1 or 2;
• A.sub.1 is (C.sub.1 -C.sub.6)alkyl, substituted (C.sub.1-6)alkyl wherein the substitutents may be as for R.sup.4 above, (C.sub.3-6)cycloalkyl, cyclohexenyl, cyclohexadienyl, phenyl, thienyl, pyridyl, thiazolyl group, a (C.sub.1-6)akylthio group or (C.sub.1-6)alkyloxy;
• X.sub.1 is a hydrogen or halogen atom, a carboxylic acid, carboxylic ester, sulphonic acid, azido, tetrazolyl, hydroxy, amino, ureido, or guanidino group;
• A.sub.2 is phenyl, 2,6-dimethoxyphenyl, 2-alkoxy-1-naphthyl, 3-arylisoxazolyl, or 3-(2-chloro-6-fluorophenyl)-5-methylisoxazol-4-yl;
• X.sub.2 is a --CH.sub.2 OCH.sub.2 --, --CH.sub.2 SCH.sub.2 -- or alkylene group;
• X.sub.3 is an oxygen or sulphur atom;
• A.sub.3 is phenyl, naphthyl, furyl, aminothiazolyl or aminothiadiazolyl in which the amino group is optionally protected;
• and A.sub.4 is hydrogen, (C.sub.1-6)alkyl, (C.sub.3-8)cycloalkyl, (C.sub.3-8)cycloalkyl(C.sub.1-6)alkyl, (C.sub.1-6)alkoxycarbonyl(C.sub.1-6)alkyl, (C.sub.2-6)alkenyl, carboxy(C.sub.1-6)alkyl, (C.sub.2-6)aklynyl, (C.sub.6 -C.sub.10) aryl or (C.sub.1-6)alkyl substituted by up to three aryl groups;
• 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 hydrolyzable ester group;
• R.sup.4 represents hydrogen or up to four substituents, which may be present on any of the carbon atoms in the ring system shown, selected from (C.sub.1 -C.sub.6) alkyl, (C.sub.2 -C.sub.6)alkenyl, (C.sub.2 -C.sub.6)alkynyl, (C.sub.1 -C.sub.6)alkoxy, hydroxy, halogen, amino, (C.sub.1 -C.sub.6)alkylamino, acylamino wherein acyl is defined as above in formulae a-f, ((C.sub.1 -C.sub.6)alkyl).sub.2 -[dialkyl]amino, CO.sub.2 R, OCOR, CONR.sub.2, SO.sub.2 NR.sub.2 where R is hydrogen or (C.sub.1 -C.sub.6)alkyl, (C.sub.6 -C.sub.10)aryl and (C.sub.2 -C.sub.9)heterocyclyl, which may be the same or different and wherein any R.sup.4 alkyl substituent is optionally substituted by one or more substituents selected from the list from which R.sup.4 is selected;
• X is S, SO, or SO.sub.2 ;
• Y is, S, SO or SO.sub.2 ;
• n is 0 or 1;
• m is 1 or 2;
• and wherein in the ring system the dotted line indicates that one pair of adjacent ring carbon atoms is joined by a C.dbd.C double bond.