Abstract: A compound of formula I ##STR1## or a salt or ester thereof. Processes for the preparation of these compounds and the use of these compounds in the preparation of further bicyclic compounds are also disclosed.

Abstract: The compounds of the formula (II): ##STR1## or pharmaceutically acceptable salts or esters thereof wherein A is a hydrogen atom or an esterifying radical; X is an alkyl group of 1-12 carbon atoms optionally substituted by a hydroxy, amino, acylamino of C.sub.1-6 alkoxy group, which substituents are not on the carbon atom adjacent to the nitrogen atom; or a C.sub.5-7 cycloalkyl group; or a phenylalkyl group wherein the carbon atom content of the alkyl part is 1-6 and the phenyl part is optionally substituted with a fluorine, bromine, chlorine, C.sub.1-6 alkyl, or C.sub.1-6 alkoxy; with the proviso that when X represents an optionally substituted phenylalkyl group and A represents C.sub.1-3 alkyl, then the --CO.sub.2 A group is attached to the alkyl part of the phenylalkyl group; have been found to be .beta.-lactamase inhibitors and antibacterial agents. Their preparation and use is described.

Abstract: Tetrazolyl derivatives of clavulanic acid are described, having the formula: ##STR1## wherein X is an optionally substituted tetrazolyl group attached via a nitrogen atom. These compounds are useful as antibiotics and .beta.-lactamase inhibitors.

Abstract: A compound of formula I ##STR1## or a salt or ester thereof. Processes for the preparation of these compounds and the use of these compounds in the preparation of further bicyclic compounds are also disclosed.

Abstract: Tetrazolyl derivatives of clavulanic acid are described, having the formula: ##STR1## wherein X is an optionally substituted tetrazolyl group attached via a nitrogen atom. These compounds are useful as antibiotics and .beta.-lactamase inhibitors.

Abstract: A compound of formula (I) or a salt or ester thereof: ##STR1## Pharmaceutical compositions comprising a compound of formula (I) or a pharmaceutically acceptable salt or pharmaceutically acceptable ester thereof are also disclosed.

Abstract: Tetrazolyl derivatives of clavulanic acid are described, having the formula: ##STR1## wherein X is an optionally substituted tetrazolyl group attached via a nitrogen atom. These compounds are useful as antibiotics and .beta.-lactamase inhibitors.

Abstract: The compounds of the formula (II): ##STR1## or pharmaceutically acceptable salts or esters thereof wherein A is a hydrogen atom or an esterifying radical; X is an alkyl group of 1-12 carbon atoms optionally substituted by a hydroxy, amino, acylamino of C.sub.1-6 alkoxy group, which substituents are not on the carbon atom adjacent to the nitrogen atom; or a C.sub.5-7 cycloalkyl group; or a phenylalkyl group wherein the carbon atom content of the alkyl part is 1-6 and the phenyl part is optionally substituted with a fluorine, bromine, chlorine, C.sub.1-6 alkyl, or C.sub.1-6 alkoxy; with the proviso that when X represents an optionally substituted phenylalkyl group and A represents C.sub.1-3 alkyl, then the --CO.sub.2 A group is attached to the alkyl part of the phenylalkyl group; have been found to be .beta.-lactamase inhibitors and antibacterial agents. Their preparation and use is described.

Abstract: The compounds of the formula (II): ##STR1## wherein R.sub.3 and R.sub.4 are as defined in relation to formula (I) and R.sub.7 is a nitro, cyano, amino or aminomethyl group, are antibacterial agents and .beta.-lactamase inhibitors. Their use and a process for their preparation are described.

Abstract: The compounds of the formula (II): ##STR1## wherein R.sub.3 and R.sub.4 are as defined in relation to formula (I) and R.sub.7 is a nitro, cyano, amino or aminomethyl group, are antibacterial agents and .beta.-lactamase inhibitors. Their use and a process for their preparation are described.

Abstract: Compounds of the formula (II): ##STR1## wherein X is sulphur or oxygen and R is hydrogen or alkyl of 1 to 3 carbon atoms, are useful for their antibacterial, .beta.-lactamase inhibitory activity and synergistic activity when combined with a penicillin or cephalosporin.

Abstract: Compounds of the formula (II): ##STR1## wherein X is sulphur or oxygen and R is hydrogen or alkyl of 1 to 3 carbon atoms, are useful for their antibacterial, .beta.-lactamase inhibitory activity and synergistic activity when combined with a penicillin or cephalosporin.

Abstract: Compounds of the formula (II): ##STR1## wherein A is a group such that CO.sub.2 A is carboxylic acid, a non-toxic salt thereof or non-toxic ester thereof; R.sub.1 is COR.sub.4 or OR.sub.5 wherein R.sub.4 is lower alkyl, lower alkenyl, lower alkyl aryl or aryl and R.sub.5 is CO.sub.2 R.sub.6, COR.sub.6 or SO.sub.2 R.sub.6 wherein R.sub.6 is lower alkyl, lower alkenyl, lower alkyl aryl or aryl; and R.sub.2 is COR.sub.8 wherein R.sub.8 is lower alkyl, lower alkenyl, lower alkyl aryl or aryl; when R.sub.1 is COR.sub.4 and R.sub.2 is COR.sub.8, R.sub.4 and R.sub.8 are joined so that the N(COR.sub.4) COR.sub.8 moiety is a 5-,6-, or 7-membered heterocyclic ring or said ring to which is fused a phenyl ring unsubstituted or substituted by one or two lower alkyl, lower alkoxyl, fluorine or chlorine; when R.sub.1 is OR.sub.5 and R.sub.2 is COR.sub.8, R.sub.5 and R.sub.8 are joined so that the N(OR.sub.5) COR.sub.