Selected compounds of formula (I) are antibacterial agents: formula (I)
wherein R2 represents a substituted or unsubstituted C1-C6
alkyl, cycloalkyl (C1-C6 alkyl)- or aryl (C1-C6
alkyl)-group, and A represents a group of formula (IA), or (IB) wherein R4
represents the side chain of a natural or non-natural alpha amino acid, and
R5 and R6 are each independently hydrogen or C1-C6
alkyl, heterocyclic or aryl (C1-C6 alkyl)-, R5
and R6 when taken together with the nitrogen atom to which they
are attached from an optionally substituted saturated heterocyclic ring of 3 to
8 atoms which ring is optionally fused to a carbocyclic or second heterocyclic
ring
##STR1##
