A compound of formula I: ** Formula ** or a pharmaceutically acceptable salt thereof, wherein: R1 is -C (O) X, wherein X is independently a protecting group, a halogen, R, -OR, -SR, -N (R) 2, a substituted or unsubstituted hydrazine 10, a substituted or unsubstituted aryl ring of 6-10 members, a substituted or unsubstituted 5-6 membered heteroaryl ring having 1-4 heteroatoms selected independently between nitrogen, oxygen or sulfur； -NO2； -PO3H； -SO3H； -CN； substituted or unsubstituted heteroaryl； or one of the following moieties: ** Formula ** in which each R is independently hydrogen or an optionally substituted group selected from C1-6 aliphatic, C1-6 heteroaliphatic, aryl, heteroaryl or a cyclic radical； R2 is a substituted or unsubstituted, branched or unbranched C10-C25 aliphatic moiety； R3 is -NH2, a peptide or -N (R4) (R5)； R4 is hydrogen or an optionally substituted group selected from C1-6 aliphatic, C1-6 heteroaliphatic, a cyclic radical, aryl or heteroaryl； R5 is heteroaryl； -C (>； = N-R6) (R7), in which R6 is selected from hydrogen, aliphatic and -N (R) 2, and R7 is selected from hydrogen, aliphatic, aryl, cyano and -SO2R； or C (O) LR8, in which L is a covalent bond or a bivalent, branched or unbranched, saturated or unsaturated C2-C6 hydrocarbon chain, in which one or more methylene units of L are independently replaced by -O- , -S-, -NH-, -C (O) -, -C (>； = CH2) - or C3-C6 cycloalkylene, in which L is optionally substituted with one or more groups selected from halogen, phenyl, a ring 8-10 membered bicyclic aryl, a 5-6 membered heteroaryl ring having 1-4 heteroatoms independently selected from nitrogen, oxygen or sulfur, an 8-10 membered bicyclic heteroaryl ring having 1-4 heteroatoms independently selected from nitrogen , oxygen or sulfur, a 5 to 7 membered monocyclic having 1-2 heteroatoms independently selected from nitrogen, oxygen or sulfur, or a 7-10 membered bicyclic heterocyclyl ring having 1-2 heteroatoms independently selected from nitro
