Aminopeptidase inhibitory activity is exhibited by compounds having the formula STR1 and pharmaceutically acceptable salts thereof, wherein R. sub.1 and R 2 are each independently hydrogen, alkyl, carboxyalkyl, halo-substituted alkyl, hydroxyalkyl, aminoalkyl, mercaptoalkyl, alkylthioalkyl, (cycloalkyl)alkyl, (heteroaryl)alkyl, arylalkyl, carbamoylalkyl, guanidinylalkyl or heteroaryl;R 3 is hydrogen, alkyl, cycloalkyl, aryl, heteroaryl, arylalkyl, (heteroaryl) alkyl, STR2 R 4 and R 5 are each independently hydrogen, alkyl, cycloalkyl, aryl, heteroaryl, arylalkyl, or (heteroaryl) alkyl;A is glycyl, alanyl, leucyl, phenylalanyl, arginyl, sarcosyl, seryl, asparagyl, lysyl, glutamyl, histidyl, tryptophyl, cysteinyl, methionyl, threonyl, tyrosyl, valyl, aspartyl, prolyl, norleucyl, or norvalyl; andn is an integer of 1 to 6.