Pharmacokinetic profile and quantitation of protection against soman poisoning by the antinicotinic compound MB327 in the guinea-pig

Current organophosphorus nerve agent medical countermeasures do not directly address the nicotinic effects of poisoning. A series of antinicotinic bispyridinium compounds has been synthesized in our laboratory and screened in vitro. Their actions can include open-channel block at the nicotinic receptor which may contribute to their efficacy. The current lead compound from these studies, MB327 1,1′-(propane-1,3-diyl)bis(4-tert-butylpyridinium) as either the diiodide (I2) or dimethanesulfonate (DMS) has been examined in vivo for efficacy against nerve agent poisoning. MB327 I2 (0–113 mg kg−1) or the oxime HI-6 DMS (0–100 mg kg− 1), in combination with atropine and avizafone (each at 3 mg kg−1) was administered to guinea-pigs 1 min following soman poisoning. Treatment increased the LD50 of soman in a dose-dependent manner. The increase was statistically significant (p < 0.01) at the 33.9 mg kg−1 (MB327) or 30 mg kg−1 (HI-6) dose with a comparable degree of protection obtained for both compounds. Following administration of 10 mg kg−1 (i.m.), MB327 DMS reached plasma Cmax of 22 μM at 12 min with an elimination t1/2 of 22 min. In an adverse effect study, in the absence of nerve agent poisoning, a dose of 100 mg kg−1 or higher of MB327 DMS was lethal to the guinea-pigs. A lower dose of MB327 DMS (30 mg kg−1) caused flaccid paralysis accompanied by respiratory impairment. Respiration normalised by 30 min, although the animals remained incapacitated to 4 h. MB327 or related compounds may be of utility in treatment of nerve agent poisoning as a component of therapy with atropine, anticonvulsant and oxime, or alternatively as an infusion under medical supervision

Protection against nerve agent poisoning by a noncompetitive nicotinic antagonist

The acute toxicity of organophosphorus (OP) nerve agents arises from accumulation of acetylcholine (ACh) and overstimulation of ACh receptors. The mainstay of current pharmacotherapy is the competitive muscarinic antagonist, atropine. Nicotinic antagonists have not been used due to the difficulties of administering a dose of a competitive neuromuscular blocker sufficient to antagonise the effects of excessive ACh, but not so much that it paralyses the muscles. An alternative approach would be to use a noncompetitive antagonist whose effects would not be overcome by increasing ACh concentrations. This study demonstrates that the compound 1,1'-(propane-1,3-diyl)bis(4-tert-butylpyridinium), which blocks open nicotinic ion channels noncompetitively, is able to reverse the neuromuscular paralysis after nerve agent poisoning in vitro and to protect guinea pigs against poisoning by nerve agents when used as part of a therapeutic drug combination including a muscarinic antagonist. In contrast to the oxime HI-6, this compound was equally effective in protecting against poisoning by sarin or tabun. Further studies should identify more effective compounds with this action and optimise doses for protection against nerve agent poisoning in vivo

Fragmentations and reactions of three isotopically labelled dimethyl methylphosphonate ions produced by electrospray ionisation in an ion trap mass spectrometer

In an initial investigation into the electrospray ionisation ion trap mass spectrometry (ESI/ITMS) of simple organophosphate esters we reported that in one of the collision induced fragmentation steps of protonated dimethyl methylphosphonate (DMMP), formaldehyde was eliminated with a concomitant partial scrambling of the methyl group attached to the phosphorus and a methoxy group. The present paper describes a further investigation of this reaction. Three novel isotopomers of DMMP were used for this study and their synthesis and properties are reported. A mechanism for the formaldehyde elimination and scrambling of the methyl groups is proposed and supported by a kinetic analysis of a limiting case. During this study black holes were found to occur in one of the ITMS instruments used and it is shown that these could lead to severe distortions in the amounts of product ions observed. A brief analysis of this observation is presented

Fragmentations and reactions of protonated O,O-dimethyl ethylphosphonate and some isotoporners produced by electrospray ionisation in an ion trap mass spectrometer

The fragmentation behaviour of protonated O,O-dimethyl ethylphosphonate and its isotopomers deuterated in the α- and β-positions of the ethyl group and their fragment ions, particularly EtP(O)OMe+(IV), have been investigated both experimentally in an ion trap mass spectrometer and theoretically by electronic structure calculations at the B3LYP level. Of particular interest is the finding that the phosphonium ion IV eliminates ethene with hydrogen/deuterium loss from both the α-and β-positions. The initial step for both routes involves ethyl migration from P to O to form the ion MeOP+OEt which then loses ethene by two mechanisms, both of which lead to the same products. That a unitary branching ratio for α- and β-elimination is not observed indicates that although the final step of dissociation into product ion and ethene is energetically the most demanding, it is not rate limiting and the large entropy change associated with the dissociation allows earlier processes to determine the branching ratio. This demonstrates once again that free energy, not enthalpy (or energy), determines the course of gas phase ion processes

Fragmentations and reactions of some isotopically labelled dimethyl methyl phosphono and trimethyl phosphoro thiolates and thionates studied by electrospray ionisation ion trap mass spectrometry

In this paper, studies on electrospray ionisation ion trap mass spectrometry of organophosphates are extended to a series of dimethyl methylphosphono and trimethyl phosphoro thionates and thiolates and some deuterated isotopomers. Of particular, interest is the comparison of the collision-induced fragmentation of ions from these compounds with those of the non-sulphur containing analogues reported previously. The thiono and thiolo isomeric structures of the sulphur containing ions analogous to I and II (see below) have very similar energies and undergo a ready interconversion. In the case of the phosphono compounds, the electronic structure calculations show that the methyl migration implicit in thiono–thiolo interconversion occurs directly and although methyl migration from P to the phosphonyl O or phosphonothionyl S can occur, the transition state (TS) energies are somewhat higher and, in the case of the migration to O, too high to take part in any of the subsequent collision induced fragmentations. With one exception, the mechanisms proposed for some of these fragmentations are supported by electronic structure calculations at the DFT-B3LYP level