Alpha-amino acid sulphonyl compounds

A compound selected from those of formula (I):

• wherein:
• represents a 5-membered, nitrogen-containing heterocycle optionally substituted by cyano,
• R1 represents hydrogen, linear or branched (C1-C6)alkyl, linear or branched (C1-C6)acyl, prolyl, alanyl, histidylprolyl or phenylalanylprolyl,
• Ak represents a linear or branched (C1-C6)alkylene chain or a heteroalkylene chain,
• X represents a single bond or phenylene optionally substituted by one or more identical or different groups selected from halogen, linear or branched (C1-C6)alkyl, hydroxy, linear or branched (C1-C6)alkoxy and linear or branched (C1-C6)polyhaloalkyl,
• R2 represents linear or branched (C1-C6)alkyl (optionally substituted by one or more identical or different groups selected from aryl, linear or branched (C1-C6)alkylsulphonyl, (C3-C7)cycloalkylsulphonyl, (C3-C7)cycloalkyl group and halogen), (C3-C10)cycloalkyl, or —NR2aR2b wherein R2a and R2b, which may be the same or different, each represent hydrogen or linear or branched (C1-C6)alkyl or, together with the nitrogen atom carrying them, form a nitrogen-containing heterocycle,
• Y represents
• R3 represents hydrogen or a group selected from linear or branched (C1-C6) alkyl, (C3-C7) cycloalkyl and aryl,
• R4, R5 and R6, which may be the same or different, each represent hydrogen or linear or branched (C1-C6)alkyl, or R4 and R6, or R5 and R6, together with the atoms carrying them, form an imidazolidine or dihydrobenzimidazole ring,
• its optical isomers and addition salts thereof with a pharmaceutically acceptable acid,
• it being understood that a nitrogen-containing heterocycle may be a saturated, monocyclic, 5- to 7-membered group containing one, two or three hetero atoms, one of those hetero atoms being the nitrogen atom and the additional hetero atom(s) optionally present being selected from oxygen, nitrogen and sulphur atoms,
• and a heteroalkylene chain may be a linear or branched (C1-C6) alkylene chain wherein a —CH2— member has been replaced by oxygen or sulphur.