Nucleophilic Reactivation of Sarin-Inhibited Acetylcholinesterase: A Molecular Modeling Study

Oximes have been used as reactivators for organophosphorus-inhibited acetylcholinesterase (AChE). However, it is still not clear why oximes are more efficient than other nucleophiles, since the reactivation consists of a simple nucleophilic substitution. In an attempt to answer this question, we have modeled the sarin-inhibited AChE reactivation by other nucleophiles (with and without the so-called alpha-effect) by applying the B3LYP/6-311G(d,p) level of theory. We have concluded that oximes reactivate AChE by a three-step mechanism in opposition to the four-step processes of the other modeled nucleophiles. In addition, our model suggests that oximes react with AChE in the deprotonated form (oximate). Our results also indicate that other nucleophiles may be used as AChE reactivators. We propose the use of hydrazones and hydrazonates for further evaluation as antidotes for intoxication by chemical warfare agents.