The invention is directed to physiologically active compounds of general formula (I): wherein: R1 represents aryl, heteroaryl or a group R3—L2—Ar1—L3—; R2 represents hydrogen or lower alkyl; R3 represents aryl or heteroaryl; and Ar1 represents an optionally substituted saturated, partially saturated or fully unsaturated 8 to 10 membered bicyclic ring system containing at least one heteroatom selected from O, S or N; Y is carboxy or an acid bioisostere; and their corresponding N-oxides or prodrugs, and pharmaceutically acceptable salts and solvates of such compounds and their corresponding N-oxides or 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).