Figure 5. Two main conjugation strategies in ADC synthesis. (A) Cysteine conjugation: reduction of interchain disulfide bonds leads to the formation of subsequent thiol groups, which react with maleimide-functionalized drug linkers to form stable thioether bonds. (B) Lysine conjugation: solvent-exposed ε-amino groups of lysines react with activated esters (e.g., NHS esters) of drug linkers to form stable amide bonds [105] (CC BY-SA 4.0).