As described on the Covalent Modifiers page, covalent modifiers can offer drug discovery scientists the ability to increase the potency and/or selectivity of small molecule inhibitors, by attachment of reactive functional groups designed to covalently bind to specific sites in a target. These interactions are often irreversible and much stronger, leading to higher affinity.
Cysteine Targeted Covalent Modifiers received huge attention from scientists as a target for covalent binding. Cysteine has relatively low abundance in proteins and high nucleophilicity, its thiolate form shows a wide range of reactivity, for example with Michael acceptors.
This residue is actively targeted in cysteine proteases and protein kinases, though selectivity can still be an issue. This problem is solved by additional modification of the compound. 
Chemspace Cysteine Targeted Covalent Modifiers Library is designed specifically to have a reactive covalent warhead, that can potentially target cysteine residues.
The compound collection is 100% modifiable and can be customized to your needs.
Write an email at email@example.com if you have any questions.
- Lonsdale, R., & Ward, R. A. (2018). Structure-based design of targeted covalent inhibitors. Chemical Society Reviews, 47(11), 3816–3830. doi:10.1039/c7cs00220c