engleski

Screening of new oximes for reactivation of tabun inhibited cholinesterases

The copper-catalyzed azide-alkyne cycloaddition reaction enabled fast and reliable synthesis of libraries of oximes that were screened for the reactivation activity of tabun-inhibited human recombinant AChE, wild type, the AChE single mutant Y337A, and human BChE. Out of 100 compounds, 53 were able to reactivate wild type AChE, but only 14 oximes restored full activity. For the remaining oximes, the maximal reactivation was below 50 %. For two most efficient reactivators of tabun-inhibited wild type AChE, detailed kinetic study of reactivation was performed and reactivation rate constants, kmax and KOX were determined. These oximes required low concentration to achieve half maximal rates of reactivation. Both oximes had similar kmax (0.02 min-1), but the affinity (i.e. 1/KOX ; KOX= 9 M) of one of the oximes was very high resulting in the overall reactivation rate constant of 2370 M-1 min-1. It appears that a distance of 8 atoms between two quaternary nitrogens is optimal to achieve high level of AChE activity. Phosphorylated choline-binding site Y337A AChE mutant was reactivated (> 80 %) with 13 oximes only. For three most efficient oximes (2-PAM analogs) the observed reactivation rate was 4-times faster than for the most efficient reactivator of AChE w.t.. Since Y337A mutant simulates the choline binding site of BChE, we tested thirty most promising reactivators of the mutant to reactivate tabun-inhibited BChE. Although only two oximes restored BChE activity over 70 %, 11 oximes reactivated tabun-inhibited BChE more efficiently than 2-PAM. A limited reactivation capacity for BChE is no surprise, since all selected oximes were designed as reactivators of phosphorylated AChE. However, our findings may provide a platform for further modifications and development of more potent antidotes in tabun poisoning.

AChE; mutants; oximes; reactvation; tabun

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