Click-chemistry-derived oxime library reveals efficient reactivators of nerve agent-inhibited butyrylcholinesterase suitable for pseudo-catalytic bioscavenging

A library of 100 click-chemistry-derived oximes was evaluated as reactivators of butyrylcholinesterase (BChE) inhibited by the nerve agents (NAs) sarin, cyclosarin, VX, and tabun. While reactivation efficiency was highly dependent on the structure of both the NA and the oxime, for each NA-BChE conjugate, we identified reactivators more effective than currently approved oximes for NA poisoning. Detailed kinetic analysis indicated that this enhancement results from both improved molecular recognition-specifically, enhanced binding affinity of the phosphylated conjugates for the oximes-and increased maximal reactivation rates. Molecular modeling of oximes in a near-attack conformation within inhibited BChE revealed critical interactions for productive reactivation. Among all tested oximes, 5B [1-hexyl-2-((hydroxyimino)methyl)pyridinium chloride] emerged as a particularly efficient reactivator for BChE phosphorylated with cyclosarin, with the highest observed overall reactivation rate of 34,120 M^-1 min^-1, which is 525-fold and 44-fold higher than the reference oximes 2-PAM and HI-6, respectively. In general, three mono-pyridinium mono-oximes demonstrated more efficient recovery of BChE activity than bis-pyridinium triazole-annulated click-chemistry bis-oximes, which were previously identified as potent reactivators for inhibited acetylcholinesterase (AChE). Ex vivo assessment of reactivation potency demonstrated that the combined addition of BChE with one efficient reactivator for BChE and another for AChE achieved > 90% reactivation of cyclosarin-inhibited cholinesterases in whole blood (WB), demonstrating near-complete degradation of a 100-fold excess of cyclosarin within 6 min. These results confirm that oxime-assisted catalysis is feasible for NA bioscavenging in blood and underscore BChE's potential as a target for developing therapies against NA poisoning.