The invention is directed to physiologically active compounds of formula (Ia): wherein R1 is optionally substituted aryl or optionally substituted heteroaryl; R2 is hydrogen, halogen, lower alkyl or lower alkoxy; R3 is alkylene, alkenylene or alkynylene; R5 is hydrogen or lower alkyl; L2 is optionally substituted alkylene or alkenylene; Y is carboxy; and Z1 is NR5; and the corresponding N-oxides, and their prodrugs; and pharmaceutically acceptable salts and solvates (e.g. hydrates) of such compounds and their N-oxides and prodrugs. Such compounds have valuable pharmaceutical properties, in particular the ability to regulate the interaction of VCAM-1 and fibronectin with the integrin VLA-4 (&agr;4&bgr;1).