Thiazolidine compounds of the general formula:
wherein Ar represents a phenyl group, a naphthyl group or a pyridyl group, Y represents a saturated or unsaturated alkylene group having 1 to 5 carbon atoms, n represents zero or 1,
represents a 5- or 6-membered saturated heterocyclic group which may contain a hetero atom other than the nitrogen atom, X represents an oxygen atom, m represents zero or 1, R represents a hydrogen atom or an alkoxycarbonyl group; and pharmaceutically acceptable salts thereof, possess an inhibitory effect for prolyl endopeptidase, and are useful as therapeutical agents for the treatment of dementia and amnesia.
Structural requirements of N-blocked L-proline derivatives as specific inhibitors for prolyl endopeptidase were investigated using a series of substrate analogs. Replacement of L-proline by its D-isomer remarkably reduced the inhibition. Introduction of a sulfur atom in proline and/or in the penultimate pyrrolidine rings significantly increased the inhibition, but the introduction of oxygen rather diminished the activity. A peptide linkage (acid-amide bond) between the proline and the pyrrolidine ring was also required to keep the inhibitory activity. A benzyloxycarbonyl group was most effective as an N-blocked component of the inhibitors.