The present invention relates to compounds of formula (I) wherein: A is a radical selected from the group comprising aromatic heterocyclic 5-membered ring systems; Ar is a radical selected from the group comprising optionally substituted 5- and 6-membered aromatic ring systems, whereby the ring system contains 0, 1, 2 or 3 heteroatoms selected from the group comprising N, O and S; Z is a linker and .PSI. is a radical of formula (II) and their use for the inhibition of integrin. ##STR00001##