Abstract: A compound of formula (I): ##STR1## wherein: R.sub.1 represents unsubstituted or substituted cycloalkyl, phenyl, naphthyl, heterocyclic, alkyl or alkenyl,A represents a bond, oxygen, sulphur, a group ##STR2## a group ##STR3## or a group ##STR4## wherein Rc represents hydrogen, alkyl or cycloalkyl, R.sub.2 represents halogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, cycloalkyl, formyl, carboxy, alkylcarbonyl, cycloalkylcarbonyl, alkoxycarbonyl, cycloalkyloxycarbonyl, optionally substituted carbamoyl, optionally substituted amino, formylamino, cyano, optionally substituted amidino, hydroxyaminomethyl, amide oxime, hydrazono, or a group selected from: ##STR5## wherein R.sub.21, R.sub.22 and R.sub.23 are as defined in the description, R.sub.