KSC-34, a covalent modifier of protein disulfide isomerase A1 (PDIA1) , is also a selective and potent a-site inhibitor of PDIA1 with an IC 50 of 3.5 μM. KSC-34 displays a 30-fold selectivity for a domain over a′ domain and displays high selectivity for PDIA1 in complex proteomes with minimal engagement of other members of the PDI family In Vitro KSC-34 is selective for PDIA1 over other members of the PDI family, and other cellular cysteine-containing proteins. KSC-34 contains a (4-phenylbutyl)methylamine diversity element for optimized binding to the active site of the a domain of PDIA1 with a chloroacetamide electrophile for covalent modification of C53 on PDIA1. MCE has not independently confirmed the accuracy of these methods. They are for reference only. Form:Solid IC50& Target:IC50: 3.5 μM (a active site of PDIA1), 104.5 μM (a′ active site of PDIA1)