Structure-activity relationships in reactivators of organophosphorus-inhibited acetylcholinesterase. V. Quaternary salts of hydroxyiminomethylimidazoles

Imidazole aldoximes effective in assisting butyrylcholinesterase catalysis of organophosphate detoxification

Intoxication by organophosphate (OP) nerve agents and pesticides should be addressed by efficient, quickly deployable countermeasures such as antidotes reactivating acetylcholinesterase or scavenging the parent OP. We present here synthesis and initial in vitro characterization of 14 imidazole aldoximes and their structural refinement into three efficient reactivators of human butyrylcholinesterase (hBChE) inhibited covalently by nerve agent OPs, sarin, cyclosarin, VX, and the OP pesticide metabolite, paraoxon. Rapid reactivation of OP–hBChE conjugates by uncharged and nonprotonated tertiary imidazole aldoximes allows the design of a new OP countermeasure by conversion of hBChE from a stoichiometric to catalytic OP bioscavenger with the prospect of oral bioavailability and central nervous system penetration. The enhanced in vitro reactivation efficacy determined for tertiary imidazole aldoximes compared to that of their quaternary N-methyl imidazolium analogues is attributed to ion pairing of the cationic imidazolium with Asp 70, altering a reactive alignment of the aldoxime with the phosphorus in the OP–hBChE conjugate.

Crystal structure of potential antidotes against nerve-gas poisoning

Compound (1), 2-hydroxyiminomethyl-1-benzylimidazole, C11H11N3O, Mr = 201.23, space group orthorhombic P212121, a = 9.496(3) Å, b = 9.850(4) Å, c = 11.024(8) Å, V = 1031.1(9) Å−3, Z = 4, Dx = 1.296 Mgm−3, λ(MoKα ) = 0.7107 Å, μ = 0.81 cm−1, F(000) = 424, T = 293 K, final R = 0.0364 for 625 independent observed reflections. An intermolecular hydrogen bond O–H … N of 2.700(4) Å stabilizes the structure.

Compound (2), 2-hydroxyiminomethyl-1-benzyl-3-methylimidazolium-iodide, C12H14IN3O, Mr = 343.17, space group orthorhombic Pbca, a = 12.484(5) Å, b = 17.339(5) Å, c = 12.616(5) Å, V = 2731(2) Å3, Z = 8, Dx = 1.669 Mgm−3, λ(MoK α) = 0.7107 Å, μ = 23.08 cm−1, F(000) = 1344, T = 293 K, final R = 0.0287 for 2104 independent observed reflections. The iodide anion is linked to the oxime-oxygen by hydrogen bond of 3.397(4) Å. Quaternization of the imidazolium ring causes the rotation of the oxime group about C–C bond connecting the imidazolium ring and oxime group.

Compound (3), 4-[(hydroxyimino)methyl]-1-[[[2-[(hydroxyimino)methyl]-3-phenyl-1 H-imidazolium-1-yl]methoxy]methyl]pyridinium diiodide, C18H19I2N5O3, Mr = 607.19, monoclinic, P21/c, a = 13.547(3) Å, b = 14.501 (3) Å, c = 11.781(2) Å, β = 102.75(2)°, V = 2257.3(8) Å3, Z = 4, Dx = 1.787 Mgm−3, λ(MoK α) = 0.7107 Å, μ = 27.82 cm−1, F(000) = 1168, T = 293 K, final R = 0.0480 for 2835 independent observed reflections. The iodide anions are linked to oxime-oxygens of the cation by hydrogen bonds of 3.336(6) and 3.388(5) Å, respectively. It has been found that the geometry of the oxime group of the imidazolium ring in the investigated structure can be compared with that of the oxime group of compound (2).

Synthesis and ocular effects of imidazole nitrolic acids

Novel 1-R-imidazole-2-nitrolic acids and 1-R-imidazole-5-nitrolic acids (R: H, Me, Bn) were synthesized from oximes by treatment with a mixture of fuming nitric acid and acetic acid. The effects of these potential nitric oxide-donating compounds were tested on ocular variables such as intraocular pressure and formation of cyclic guanosine-3,5'-monophosphate in the incubation of porcine iris-ciliary body.

Quaternary salts of 3,3'-bis-pyridinium monooximes: synthesis and biological activity

Two new series of asymetrically substituted 3,3'-bis-pyridinium monooximes bridged by oxopropane and propane groups were synthesized and characterized by spectral data and acid dissociation constants (pKas). Both the in vitro reactivation potency, in experiments with lyophilized electric eel acetylcholinesterase (AChE) inhibited by diisopropylfluorophosphate, and in vivo protection efficacy against diisopropylfluorophosphate intoxication in mice of these compounds were evaluated and compared with those of trimedoxime and 2-pyridine-aldoxime methiodide. The compounds were also evaluated for in vitro inhibition of AChE. The compounds with the oxopropane link were stronger inhibitors and weaker reactivators than the corresponding propane derivatives. No significant correlation was observed among pKa, oxime inhibition of AChE, reactivation of inhibited AChE, and protection index. Changing substituents in pyridine rings or altering linking groups between pyridine rings did not improve antidotal efficacy compared with trimedoxime and 2-pyridine-aldoxime methiodide.