Compounds of formula (II) are antibacterial agents wherein Q represents a radical of the formula: —N(OH)CH(═O) or the formula: —C(═O)NH(OH); R
1
represents hydrogen, C
1
-C
6
alkyl or C
1
-C
6
alkyl substituted by one or more halogen atoms, or, except when Q is a radical of the formula: —N(OH)CH(═O), a hydroxy, C
1
-C
6
alkoxy, C
1
-C
6
alkenyloxy, amino, C
1
-C
6
alkylamino, or di-(C
1
-C
6
alkylamino group; R
2
represents a substituted or unsubstituted C
1
-C
6
alkyl, cycloalkyl(C
1
-C
6
alkyl)- or aryl(C
1
-C
6
alkyl)-group; and A represents a group of formula (IIA), or (IIB) wherein R
4
represents the side chain of a natural or non-natural alpha amino acid, and R
5
and R
6
when taken together with the nitrogen atom to which they are attached form a saturated heterocyclic first ring of 5 to 7 atoms as specified in the description.
Compounds of formula (II) are antibacterial agents wherein Q represents a radical of the formula: —N(OH)CH(═O) or the formula: —C(═O)NH(OH); R
1
represents hydrogen, C
1
-C
6
alkyl or C
1
-C
6
alkyl substituted by one or more halogen atoms, or, except when Q is a radical of the formula: —N(OH)CH(═O), a hydroxy, C
1
-C
6
alkoxy, C
1
-C
4
alkenyloxy, amino, C
1
-C
4
alkylamino, or di-(C
1
-C
6
alkyl)amino group; R
2
represents a substituted or unsubstituted C
1
-C
6
alkyl, cycloalkyl(C
1
-C
6
alkyl)- or aryl(C
1
-C
6
alkyl)-group; and A represents a group of formula (IIA), or (IIB) wherein R
4
represents the side chain of a natural or non-natural alpha amino acid, and R
5
and R
6
when taken together with the nitrogen atom to which they are attached form a saturated heterocyclic first ring of 5 to 7 atoms as specified in the description.