engleski

New reactivators of tabun-inhibited acetylcholinesterase synthesised by click chemistry

Application of the [3+2] cycloaddition reaction between alkynes and azides (“ Click reaction” ) as a combinatorial approach allows for the fast and reliable synthesis of libraries of new reactivators that were screened toward reactivation of tabun-inhibited human recombinant AChE, wild type and the single mutant Y337A. The screening was done using single concentration of oxime, 1 mM or lower when inhibition of the enzyme by oxime was significant. Out of 57 compounds, 24 were able to reactivate wild type AChE but only 13 oximes fully. For the remaining 33 oximes the maximal reactivation was below 30 %. This deviation could be due to the post-inhibitory dealkylation of the phosphorylated enzyme or re-inhibition of the active enzyme by the phosphorylated oxime that depends on its stability and on structure of oxime. For two most efficient reactivators of tabun-inhibited wild type AChE individual 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 apparent 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 seems that a distance of 8 atoms between two quaternary nitrogens yields the most optimal compound for the reactivation of the tabun-AChE. Eighteen most promising reactivators of the AChE wild type were then also screened for reactivation of tabun phosphorylated choline-binding site Y337A AChE mutant. The highest efficiency was obtained for 2-PAM analogs. Reactivators most efficient for the wild type AChE reactivation did not show further enhancement of their reactivation potency for the mutated AChE.

reactivators; oximes; tabun; inhibition; acetylcholinesterase; click-chemistry

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