A Structure-Activity Analysis of the Variation in Oxime Efficacy Against Nerve Agents
ARMY MEDICAL RESEARCH INST OF CHEMICAL DEFENSE ABERDEEN PROVING GROUND MD
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A structure-activity analysis was used to evaluate the variation in oxime efficacy of 2-PAM, obidoxime, HI-6 and ICD585 against nerve agents. In vivo oxime protection and in vitro oxime reactivation were used as indicators of oxime efficacy against VX, sarin, VR and cyclosarin. Analysis of in vivo oxime protection was conducted with oxime protective ratios PR from guinea pigs receiving oxime and atropine therapy after sc administration of nerve agent. Analysis of in vitro reactivation was conducted with second-order rate contants kr2 for oxime reactivation of agent-inhibited acetylcholinesterase AChE from guinea pig erythrocytes. In vivo oxime PR and in vitro kr2 decreased as the volume of the alkylmethylphosphonate moiety of nerve agents increased from VX to cyclosarin. This effect was greater with 2-PAM and obidoxime N14-fold decrease in PR than with HI-6 and ICD585 b3.7-fold decrease in PR. The decrease in oxime PR and kr2 as the volume of the agent moiety conjugated to AChE increased was consistent with a steric hindrance mechanism. Linear regression of log PR-1 against log kr2 oxime dose produced two offset parallel regression lines that delineated a significant difference between the coupling of oxime reactivation and oxime protection for HI-6 and ICD585 compared to 2-PAM and obidoxime. HI-6 and ICD585 appeared to be 6.8-fold more effective than 2-PAM and obidoxime at coupling oxime reactivation to oxime protection, which suggested that the isonicotinamide group that is common to both of these oximes, but absent from 2-PAM and obidoxime, is important for oxime efficacy.
- Chemical, Biological and Radiological Warfare