Protected HDAC (histone deacetylase) inhibitors

A compound of formula I:

• in which:
• R1 is H or an alkyl group comprising 1 to 10 carbon atoms;
• R2 is P—Z, in which P is an alkyl group comprising from 1 to 15 carbon atoms, optionally substituted with one or more of N atoms, —C═O, and —NHC═O;
• and Z is:
• in which R3 is H, a C1-C9 alkyl, —CH2OH, —CH2OCH3, -Ph, —C6H4OH, —CH(CH3)OH, —C(CH2COOH)2OH, —C(═O)CH3, —CH2NH2, —CH2NH(C═O)CH2NH2, or —CH2NH(C═O)CH2NH(C═O)CH2NH2;
• Or
• R1 and R2 form part of a heterocyclic group Y having 5 or 6 members and being substituted with P-Z, wherein P is as defined above, and wherein Z is as defined above;
• Ar1 and Ar2 are each, independently, selected from a phenyl, pyridine, pyrimidine, thiophene, furan, benzofuran or thiazole group;
• and
• X is —C═C—C(═O)OR4, in which R4 is an alkyl group comprising from 1 to 10 carbon atoms, optionally substituted with one or more O atoms.