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Two methods for the synthesis of a new unsymmetric bispyridinium oxime-1-(4-hydroxyiminomethylpyridinium)-3-(carbamoylpyridinium)propane dibromide are described. In vitro efficacy of this new oxime to reactivate sarin-inhibited acetylcholinesterase has been evaluated.

Synthesis of a new asymmetric bisquaternary reactivator of tabun-inhibited acetylcholinesterase-1-(4-hydroxyiminomethylpyridinium)-4-(4-carbamoylpyridinium) butane dibromide is described. Reactivation potency of this oxime is compared to the currently used reactivators-pralidoxime, obidoxime and H-oxime HI-6.

The efficacy of two new monopyridinium oximes (2-PAAM, 2-PAEM) and two bispyridinium oximes (obidoxime. HI-6) was tested in combination with atropine sulphate against acute poisoning with the organophosphorus insecticide mevinphos in mice. When mice were treated two min. after mevinphos poisoning, no significant differences in the therapeutic effect of tested oximes were observed. The oximes increased the 24 hr LD50 values of mevinphos about two times in comparison with the 24 hr LD50 values of mevinphos in mice protected with atropine sulphate alone and more than three times in comparison with non-treated intoxicated animals. On the other hand, both monopyridinium oximes were significantly more efficacious than HI-6 and as efficacious as obidoxime when they were administered 30 sec. after mevinphos poisoning. Both monopyridinium oximes and obidoxime increased the 24 hr values of mevinphos almost three times in comparison with the 24 hr values of mevinphos in mice protected with atropine sulphate alone and about twenty-five times in comparison with non-treated intoxicated animals, while the oxime HI-6 less than two times in comparison with the 24 hr values of mevinphos in mice protected with atropine sulphate alone and about fifteen times in comparison with non-treated intoxicated animals. Use of new monopyridinium oximes seems to be the improvement in the antidotal treatment of poisoning with organophosphorous insecticide mevinphos in comparison with HI-6 but not in comparison with obidoxime when oximes are used in equimolar doses.

The kinetics was studied of the inhibition of solubilized rat brain acetylcholinesterase by 9-hydrazino-1,2,3,4-terahydroacridine (THH) and 9-amino-10-methyl-1,2,3,4-tetrahydroacridinium (QTHA); the inhibitory effect was compared with the effect of tacrine (9-amino-1,2,3,4-tetrahydroacridine, THA). It was observed that THH is a reversible, noncompetitive inhibitor of rat brain acetylcholinesterase (Ki = 0.16 μM) and that it binds, similarly to THA, to the hydrophobic domain of the active center of acetylcholinesterase thus simultaneously inhibiting the formation of complex ES2 with acetylcholine as substrate. This eliminates the inhibition of acetylcholinesterase by an excess of substrate. QTHA is a mixed, competitive-non-competitive inhibitor characterized by KI comp = 5.3 μM and Ki noncomp = 0.08 μM. QTHA binds to an entirely different site of the active surface of acetylcholinesterase than THA and THH. This binding site is most likely the so-called β-anionic or also peripheric anionic site to which, e.g. atropine is also bound. Both inhibitors studied form with acetylcholinesterase a reversible, enzymatically inactive complex in which one inhibitor molecule is bonded to each active center of the enzyme.