Compounds of formula (I) wherein Ar is carbocyclic or heterocyclic aryl, or biaryl; Q is O, S or N-C N; X is arylene; V is NH, O, NHOH, CH2 or a direct bond; W is NH, O, NHOH, CH2 or a direct bond; Alk is C2-C7-alkylene or C2-C7-alkylene interrupted by O, S, SO, SO2 or NR3; Y is amino, acylamino, mono- or di- (lower alkyl, aryl or aralkyl)-amino, pyrrolidino, perhydroazepino or a group of the formula (II) in which M1 is N; and M2 is CH2, O, NR3, S, SO or SO2; R1, R2 and R3 are independently hydrogen, lower alkyl, lower alkenyl, cycloalkyl, aryl, cycloalkyl-lower alkyl, aryl-lower alkyl or aryl-lower alkenyl; Z is lower alkylene or lower alkylene substituted by one or more of lower alkyl, lower alkenyl, cycloalkyl, aryl, cycloalkyl-lower alkyl, aryl-lower alkyl or aryl-lower alkenyl; or Z is lower alkylene interrupted by O, S, SO, SO2 or NR3; pharmaceutically acceptable esters and amides thereof; and pharmaceutically acceptable salts thereof, which are useful as VLA-4 integrin antagonists.