Compared with traditional non-covalent inhibitors, covalent inhibitors can achieve higher binding affinity and longer residence time. These characteristics can be realized into lower doses, dosing frequency and systemic exposure of drugs. Therefore, many pharmaceutical companies have initiated drug development programs for covalent inhibitors of various enzymes. Once the ligand is docked into the binding site, the warhead will form a covalent bond with nearby amino acid residues. By designing inhibitors so that covalent bonds are only formed on non-catalytic residues with poor conservation, the target selectivity can be maximized.