Poststatin analogues containing (S)-2-oxo-2-(2-pyrrolidinyl) acetyl moiety in P 1 were synthesized and examined for their inhibitory activity against prolyl endopeptidase and cathepsin B in vitro. Introduction of non-peptidyl cycloalkylamine component in P'1 was effective and P 3-acyl groups must be widely modifiable for prolyl endopeptidase inhibition. Acyl-L-phenylalanyl-(S)-2-oxo-2-(2-pyrrolidinyl) acetyl-cycloalkylamide type compounds ...