Targeted covalent inhibitors represent a viable strategy to block protein kinases involved in different disease pathologies. Although a number of computational protocols have been published for identifying druggable cysteines, experimental approaches are limited for mapping the reactivity and accessibility of these residues. Here, we present a ligand based approach using a toolbox of fragment-sized molecules with identical scaffold but equipped with diverse covalent warheads. Our library represents a unique opportunity for the efficient integration of warhead-optimization and target-validation into the covalent drug development process. Screening this probe kit against multiple kinases could experimentally characterize the accessibility and reactivity of the targeted cysteines and helped to identify suitable warheads for designed covalent inhibitors. The usefulness of this approach has been confirmed retrospectively on Janus kinase 3 (JAK3). Furthermore, representing a prospective validation, we identified Maternal embryonic leucine zipper kinase (MELK), as a tractable covalent target. Covalently labelling and biochemical inhibition of MELK would suggest an alternative covalent strategy for MELK inhibitor programs.

靶向共价抑制剂代表一种可行的策略来阻断涉及不同疾病病理的蛋白激酶。尽管已发布了许多用于识别可药物化半胱氨酸的计算方案，但实验方法在绘制这些残基的反应性和可及性方面受到限制。在这里，我们提出了一种基于配体的方法，该方法使用具有相同支架但配备有多种共价战斗部的片段大小分子的工具箱。我们的图书馆为将战斗部优化和目标确认有效地整合到共价药物开发过程中提供了独特的机会。针对多种激酶筛选该探针试剂盒可通过实验表征目标半胱氨酸的可及性和反应性，并有助于为设计的共价抑制剂确定合适的战斗部。回顾性地在Janus激酶3（JAK3）上证实了这种方法的有效性。此外，代表了前瞻性验证，我们确定了母体胚胎亮氨酸拉链激酶（MELK）为可处理的共价靶标。共价标记和MELK的生化抑制将建议MELK抑制剂计划的替代共价策略。