Charged linkers and their uses for conjugation

A cell-binding agent-drug conjugate of formula (II)

• wherein:
• Cb represents a cell-binding agent which is an antibody, or a fragment thereof;
• Drug represents a drug;
• n is an integer from 1 to 20;
• and
• the cell-binding agent-drug conjugate of formula (II) is formed by reacting a functional group on the drug with Z in a compound of formula (I), and reacting a functional group on the cell-binding agent with Y:
• wherein Y is selected from the group consisting of an unsubstituted or substituted N-hydroxysuccinimide ester, hydrazide, p-nitrophenyl ester, dinitrophenyl ester, pentafluorophenyl ester, pyridyldisulfide, nitropyridyldisulfide, unsubstituted or substituted maleimido, β-maleimidopropionamido, haloacetate and carboxylic acid halide;
• Z is a thiol, disulfide, pyridyldisulfide, —ONH2, carboxy, aldehyde, ketone, azide, unsubstituted or substituted maleimido, N-hydroxy succinimide ester, haloacetyl, halogen, hydrazine or hydroxy group;
• M is H, Na, K, N+R1R2R3 or a pharmaceutical salt thereof;
• R1 and R2 are the same or different and are a linear alkyl having from 1 to 6 carbon atoms, branched or cyclic alkyl having from 3 to 6 carbon atoms, a linear, branched or cyclic alkenyl or alkynyl having from 2 to 6 carbon atoms, a polyethyleneoxy unit of formula (OCH2CH2)p, wherein p is an integer from 1 to about 1000, or a combination thereof;
• R3 is absent, a linear alkyl having from 1 to 6 carbon atoms, branched or cyclic alkyl having from 3 to 6 carbon atoms, a linear, branched or cyclic alkenyl or alkynyl having from 2 to 6 carbon atoms, a polyethyleneoxy unit of formula (OCH2CH2)p, wherein p is an integer from 1 to about 1000, or a combination thereof;
• and
• R4, and R5, are the same or different and are absent, H, a linear alkyl having from 1 to 6 carbon atoms, branched or cyclic alkyl having from 3 to 6 carbon atoms, linear, branched or cyclic alkenyl or alkynyl having from 2 to 6 carbon atoms, or polyethyleneoxy unit of formula (OCH2CH2)p-1OCH2CH3, wherein p−1 is an integer from 1 to about 1000, or a combination thereof.