A compound of formula (I) or a salt, N-oxide, hydrate or solvate thereof e.g. Cyclopentyl (2S)-cyclohexyl({ 4-[(1E)-3-(hydroxyamino)-3-oxoprop-1-en-1-yl]benzyl} amino)acetate wherein A, B and D independently represent =C- or =N- R1 is an ester group which is hydrolysable by one or more intracellular carboxyesterase enzymes to a carboxylic acid group R2 is the side chain of a natural or non-natural alpha amino acid Y is a bond, -C(=O)-, -S(=O)2-, -C(=O)O-, -C(=O)NR3-, -C(=S)-NR3 , -C(=NH)NR3 or -S(=O)2NR3- wherein R3 is hydrogen or optionally substituted C1-C6 alkyl L1 is a divalent radical of formula -(Alk1)m(Q)n(Alk2)p- wherein m, n and p are independently 0 or 1, Q is (i) an optionally substituted divalent mono- or bicyclic carbocyclic or heterocyclic radical having 5 - 13 ring members, or (ii), in the case where both m and p are 0, a divalent radical of formula -X2-Q1- or -Q1-X2- wherein X2 is -O-, S- or NRA- wherein RA is hydrogen or optionally substituted C1-C3 alkyl, and Q1 is an optionally substituted divalent mono- or bicyclic carbocyclic or heterocyclic radical having 5 - 13 ring members, Alk1 and Alk2 independently represent optionally substituted divalent C3-C7 cycloalkyl radicals, or optionally substituted straight or branched, C1-C6 alkylene, C2-C6 alkenylene ,or C2-C6 alkynylene radicals which may optionally contain or terminate in an ether (-ORECIEVED ), thioether (-S-) or amino (-NRA-) link wherein RA is hydrogen or optionally substituted C1-C3 alkyl X1 represents a bond -C(=O) or -S(=O)2- -NR4C(=O)-, -C(=O)NR4-,-NR4C(=O)NR5- , -NR4S(=O)2-, or -S(=O)2NR4- wherein R4 and R5 are independently hydrogen or optionally substituted C1-C6 alkyl and z is 0 or 1 Furthermore, also disclosed is a pharmaceutical composition comprising a compound of formula (I), and the use of compound of formula (I) in the preparation of a medicament for the treatment of cancer cell proliferation, Huntingtons disease, Alzheimers disease, or rheumatoid arthritis.
