A compound of formula (I) or a pharmaceutically or veterinarily acceptable
salt thereof for the inhibition of activity of bacterial PDF enzyme:
##STR00001## wherein A represents a group of formula (IA) or (IB)
##STR00002## and wherein R.sub.1 is hydrogen, R.sub.2 is n-butyl, benzyl
or cyclopentylmethyl, R.sub.3 is hydrogen, R.sub.4 is tert-butyl,
iso-butyl, benzyl or methyl, R.sub.5 is hydrogen or methyl and R.sub.6 is
methyl.