Conjugation linkers, cell binding molecule-drug conjugates containing the linkers, methods of making and uses such conjugates with the linkers

A cell-binding agent-drug conjugate compound of Formula

• wherein in Formula (V′),
• Cb, Cb′ and Cb″ represent same or different, a cell-binding molecule of an antibody or an antibody fragment;
• represents either single bond or double bond;
• X1, X1, X1″, L2, L2′ and L2″ are absent;
• m1, m2, m3, m4, m4′, m4″, m5, m5′, and m5″ are independently an integer from 1 to 10,
• L1 is an amide wherein a nitrogen atom in the amide is bonded to R1;
• R1 is an alkyl carbonyl wherein the carbonyl is bonded to Drug;
• T is
• wherein indicates a bonding site to L1 and mint indicates a bonding site to a CO group;
• Tis Drug is a tubulysin compound.