A compound of formula, or one of its pharmaceutically acceptable salts: wherein: W is For Cl; -X-Y- is -C=C- or -X-Y- is Br and R2 does not exist; R1 is H; Z is =N-OH; R2 is a group chosen from aralkyl, preferably phenyl propyl, or a compound of formula, or one of its pharmaceutically acceptable salts: wherein: -X-Y- is -CH2-CH2-, -C=C-, -CH=CH-, or -X-Y- is Br and R2 does not exist; R1 is H, NHOH or -NH2; Z is O or =N-OH; R2 is a group chosen from alkyl, haloalkyl, hydroxyalkyl, aryl, aralkyl, heteroaryl, heterocyclyl, halogen, cyano; R-O-CO-R'- wherein R and R' are both independently alkyl groups; -R3-N, alkylsulfonamide, alkenyl, a biomolecule, a fluorescent probe, radical A and radical B, wherein radical A or radical B may be linked to -Y-X- by an alkyl group, preferably an ethyl group: or R2 is an alkyl group linked to the following radical: R3 is an alkyl group, and R4 and R5 are identical or different and each independently represent H, R6-O-CO- with R6 being an alkyl group, a carboxybenzyl group, a pyridine group (preferably a 4-pyridino), a 7-chloro-2,3-dihydro-1H-cyclopenta[b]quinolin-9-yl radical, a quinolin-4-yl radical, an acridin-9-yl radical or R4 and R5 form together with the nitrogen atom a 1,3-dioxoisoindolin-2-yl, wherein said biomolecule is a sugar moiety, a peptide moiety comprising 1 to 50 amino acids, a protein moiety comprising at least 51 amino acids, or a DNA or RNA moiety, and said fluorescent probe is a chemical function or a fluorophore endowed with fluorescent properties, with the exception of 6-bromo-3-fluoro-2-pyridine hydroxamic acid, of 6-bromo-3-fluoropicolinaldehyde and of 6-bromo-3-fluoro-2-pyridinecarboxamide. W is For Cl; -X-Y- is -C=C- or -X-Y- is Br and R2 does not exist; R1 is H; Z is =N-OH; R2 is a group chosen from aralkyl, preferably phenyl propyl, or a compound of formula, or one of its pharmaceutically acceptable salts: wherein: -X-Y- is -CH2-CH2-, -C=C-, -CH=CH-, or -X-Y- is Br and R2 does not exist; R1 is H, NHOH or -NH2; Z is O or =N-OH; R2 is a group chosen from alkyl, haloalkyl, hydroxyalkyl, aryl, aralkyl, heteroaryl, heterocyclyl, halogen, cyano; R-O-CO-R'- wherein R and R' are both independently alkyl groups; -R3-N, alkylsulfonamide, alkenyl, a biomolecule, a fluorescent probe, radical A and radical B, wherein radical A or radical B may be linked to -Y-X- by an alkyl group, preferably an ethyl group: or R2 is an alkyl group linked to the following radical: R3 is an alkyl group, and R4 and R5 are identical or different and each independently represent H, R6-O-CO- with R6 being an alkyl group, a carboxybenzyl group, a pyridine group (preferably a 4-pyridino), a 7-chloro-2,3-dihydro-1H-cyclopenta[b]quinolin-9-yl radical, a quinolin-4-yl radical, an acridin-9-yl radical or R4 and R5 form together with the nitrogen atom a 1,3-dioxoisoindolin-2-yl, wherein said biomolecule is a sugar moiety, a peptide moiety comprising 1 to 50 amino acids, a protein moiety comprising at least 51 amino acids, or a DNA or RNA moiety, and said fluorescent probe is a chemical function or a fluorophore endowed with fluorescent properties, with the exception of 6-bromo-3-fluoro-2-pyridine hydroxamic acid, of 6-bromo-3-fluoropicolinaldehyde and of 6-bromo-3-fluoro-2-pyridinecarboxamide. -X-Y- is -CH2-CH2-, -C=C-, -CH=CH-, or -X-Y- is Br and R2 does not exist; R1 is H, NHOH or -NH2; Z is O or =N-OH; R2 is a group chosen from alkyl, haloalkyl, hydroxyalkyl, aryl, aralkyl, heteroaryl, heterocyclyl, halogen, cyano; R-O-CO-R'- wherein R and R' are both independently alkyl groups; -R3-N, alkylsulfonamide, alkenyl, a biomolecule, a fluorescent probe, radical A and radical B, wherein radical A or radical B may be linked to -Y-X- by an alkyl group, preferably an ethyl group: or R2 is an alkyl group linked to the following radical: R3 is an alkyl group, and R4 and R5 are identical or different and each independently represent H, R6-O-CO- with R6 being an alkyl group, a carboxybenzyl group, a pyridine group (preferably a 4-pyridino), a 7-chloro-2,3-dihydro-1H-cyclopenta[b]quinolin-9-yl radical, a quinolin-4-yl radical, an acridin-9-yl radical or R4 and R5 form together with the nitrogen atom a 1,3-dioxoisoindolin-2-yl, R4 and R5 are identical or different and each independently represent H, R6-O-CO- with R6 being an alkyl group, a carboxybenzyl group, a pyridine group (preferably a 4-pyridino), a 7-chloro-2,3-dihydro-1H-cyclopenta[b]quinolin-9-yl radical, a quinolin-4-yl radical, an acridin-9-yl radical or R4 and R5 form together with the nitrogen atom a 1,3-dioxoisoindolin-2-yl, wherein said biomolecule is a sugar moiety, a peptide moiety comprising 1 to 50 amino acids, a protein moiety comprising at least 51 amino acids, or a DNA or RNA moiety, and said fluorescent probe is a chemical function or a fluorophore endowed with fluorescent properties, with the exception of 6-bromo-3-fluoro-2-pyridine hydroxamic acid, of 6-bromo-3-fluoropicolinaldehyde and of 6-bromo-3-fluoro-2-pyridinecarboxamide.