Alpha-amino acid derivatives, process for their preparation and their use as inhibitors of dipeptidyl peptidase IV (DPP IV).

Compound of formula (I): (see formula) where ~ (See formula) represents a nitrogenous heterocycle of 5 members optionally substituted by a cyano group, ~ Ak represents a (C1-C6) linear or branched alkylene chain, ~ X represents a single bond or a phenylene group, ~ R1 and R2, identical or different, each represent a hydrogen atom or an alkyl group (C1-C6) alkyl, ~ Y represents NR4 or CH-NO2, ?R4 represents an atom hydrogen or an alkyl group (C1-C6) alkyl group, ~ R3 represents: - either a linear or branched (C1-C6) group selected from alkyl, nitro and cyano, in the case where Y represents CH- NO2, - or a group selected from nitro and cyano, when Y represents NR4, their tautomers if they exist, its optical isomers and its addition salts with a pharmaceutically acceptable acid, excluding compounds in which simultaneously (see formula) represents a 5-membered heterocyclic nitrogenous no substituted, Ak represents the group - (CH2) 3-, X represents a single bond, Y represents NH and R3 represents the nitro group, it being understood that 5-membered nitrogen heterocycle means a saturated monocyclic 5-membered group containing one, two or three heteroatoms, these heteroatoms being one of a nitrogen atom, and being selected or additional heteroatoms optionally present from oxygen, nitrogen or sulfur.