The present invention relates to novel inhibitors of prolyl endopeptidase of formula 1 W--KCONH--X--CON--Y--CO--Z (1) wherein K, W, X, Y and Z are specified in the description.The compounds are useful for the treatment of diseases such as mild cognitive impairment (MCI), Alzheimer's disease, Down Syndrome, Parkinson disease and Chorea Huntington.