Study of para-Quinone Methide Precursors toward the Realkylation of Aged Acetylcholinesterase

Abstract

Acetylcholinesterase (AChE) is an essential enzyme that can be targeted by organophosphorus (OP) compounds, including nerve agents. Following exposure to OPs, AChE becomes phosphylated (inhibited) and undergoes a subsequent aging process where the OP-AChE adduct is dealkylated. The aged AChE is unable to hydrolyze acetylcholine, resulting in accumulation of the neurotransmitter in the central nervous system (CNS) and elsewhere. Current therapeutics are only capable of reactivating inhibited AChE. There are no known therapeutic agents to reverse the aging process or treat aged AChE. Quinone methides (QMs) have been shown to alkylate phosphates under physiological conditions. In this study, a small library of novel quinone methide precursors (QMPs) has been synthesized and examined as potential alkylating agents against model nucleophiles, including a model phosphonate. Computational studies have been performed to evaluate the affinity of QMPs for the aged AChE active site, and preliminary testing with electric eel AChE has been performed.

Demonstration of In Vitro Resurrection of Aged Acetylcholinesterase after Exposure to Organophosphorus Chemical Nerve Agents

“…We previously conducted molecular-docking and molecular-dynamics (MD) simulations to evaluate the potential orientation of QMPs at the active site of methylphosphonateaged human AChE (huAChE). 25 In this work, a larger library of QMPs was studied through this modeling approach using an in silico model of aged huAChE.…”

“…We determined that pyridyl compounds had a higher propensity to be bound in the active site and close to the phosphyl oxyanion as compared with their phenyl analogues. 25 Moreover, 3-hydroxypyridine-derived QMPs with the reactive benzylic carbon attached at the 2-position displayed promising interactions. Of the 72 compounds modeled, 6 of the top 10 compounds (Figure S2) were members of that specific 3-hydroxypyridine framework.…”

Resurrection and Reactivation of Acetylcholinesterase and Butyrylcholinesterase

“…Given the provenp otential of QMs and QMPs, Hadad and co-workersb egan an initial study to determine if theset ypes of compounds would be sufficient to recover the activity of aged AChE. [159] A total of eight different compounds were synthesized on the basis of av anillin framework with various amine leaving groups in both the protonated and deprotonated forms, 93-96 and 97-100 ( Figure 45). First, the compounds were tested with model nucleophiles (4-methylbenzenethiol,p iperidine, and benzyl al- Figure 44.…”

“…QMP structures used in reaction with nucleophiles for proof of principle alkylation. [159] cohol) for their re-alkylation abilities. The compounds were incubated with the nucleophiles at 100 8Cf or 3h and the conversion waso bserved.…”

Reactivity of [(PNP)Mn(CO)2] with Organophosphates

“…Consequently, the treatment for nerve agent exposure must begin promptly to avoid “aging” of the OPA in the active site of the enzyme. Only recently have electrophilic molecules been investigated to reactivate aged OPA–enzyme complexes. , Development of an ambiphilic therapeutic that can target both the primary adduct and the “aged″ OPA adduct could facilitate the hydrolysis of the serine–phosphorus bond, reactivating the enzyme at any time after exposure (Figure , bottom).…”