Targeting organophosphorus compounds poisoning by novel quinuclidine-3 oximes: development of butyrylcholinesterase-based bioscavengers

A library of 14 mono-oxime quinuclidinium-based compounds with alkyl or benzyl substituent were synthesized and characterized in vitro as potential antidotes for organophosphorus compounds (OP) poisoning treatment. We evaluated their potency for reversible inhibition and reactivation of OP inhibited human acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) and evaluated interactions by molecular docking studies. The reactivation was notable for both AChE and BChE inhibited by VX, cyclosarin, sarin and paraoxon, if quinuclidinium compounds contained the benzyl group attached to the quinuclidinium moiety. Out of all 14, oximeQ8[4-bromobenzyl-3-(hydroxyimino)quinuclidinium bromide] was singled out as having the highest determined overall reactivation rate of approximately 20,000 M-1 min(-1)for cyclosarin-inhibited BChE. Furthermore, this oxime in combination with BChE exhibited a capability to act as a bioscavenger of cyclosarin, degrading within 2 h up to 100-fold excess of cyclosarin concentration over the enzyme. Molecular modeling revealed that the position of the cyclohexyl moiety conjugated with the active site serine of BChE directs the favorable positioning of the quinuclidinium ring and the bromophenyl moiety ofQ8, which makes phosphonylated-serine easily accessible for the nucleophilic displacement by the oxime group ofQ8. This result presents a novel scaffold for the development of new BChE-based bioscavengers. Furthermore, a cytotoxic effect was not observed forQ8, which also makes it promising for further in vivo reactivation studies.