A compound of the formula (I): R1-A-X-NHCO???Y???R2 wherein R1 is heterocyclic group which may have suitable substituents, or phenyl which may have suitable substituents, R2 is condensed phenyl which may have suitable substituents, phenyl which may have suitable substituents, or thienyl which may have suitable substituents, A is a group of the formula: ???(CH2)t???(O)m???