DETERMINATION OF A NOVEL COGNITIVE ENHANCER, X9121, AND ITS MONO N-OXIDE METABOLITE, XG696, IN DOG PLASMA BY REVERSED-PHASE HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY WITH ULTRAVIOLET DETECTION

A selective and sensitive high-performance liquid chromatographic assa y for a novel cognitive enhancer, X9121 (I), and its mono N-oxide meta bolite, XG696 (II), in dog plasma has been developed. Compounds I, II and internal standard (I.S.) were first extracted from dog plasma usin g a solid-phase Bond Elut Certify I 10-ml LRC reservoir extraction car tridge. Chromatographic separation of I, II and I.S, was conducted on a reversed-phase Zorbax Stable Bond cyano column. Ammonium acetate buf fer (0.05 M, pH 6)-acetonitrile-triethylamine (75:25:0.1, v/v) was use d as the mobile phase. Detection of all three compounds was by UV ligh t absorbance at 313 nm. Using 0.5 ml of dog plasma for extraction, the minimum quantifiable limit was 10 ng/ml and the assay was linear from 10 to 5400 ng/ml. The coefficients of variation for intra-day precisi on ranged from 2.2 to 8.5% for I and from 2.5 to 9.8% for II. The coef ficients of variation for the inter-day precision for these two compou nds ranged from 2.6 to 9.0% and from 3.6 to 16.2%, respectively. The a bsolute percent differences for the accuracy results were within 11.0% of the spiked concentrations. Compounds I and II were stable in froze n plasma at -20 degrees C for at least 67 days.