The observation of an interference peak in plasma samples from dogs dosed with compound I led to the discovery of an unidentified metabolite. The unknown metabolite had the same molecular weight as the parent drug, and their fragmentation profiles were also quite similar. LC/MS/MS analysis of the plasma extracts of dogs and rats dosed with I and its deuterium-labeled analogue suggested a nitrone structure for the unknown metabolite. Synthesized nitrone matched the unknown metabolite with identical retention time and nearly identical fragmentation profile. The nitrone slowly decomposed in acidic aqueous solution at ambient temperature and also underwent in-source, thermal-induced hydrolysis during electrospray ionization mass spectrometric analysis. The reaction of the nitrone with diethyl acetylenedicarboxylate readily generated a [2 + 3] cycloaddition product. The example shown here clearly demonstrates that precautions must be taken when LC/MS/MS quantitation is conducted in the selected reaction monitoring mode.
从服用化合物 I 的狗血浆样本中观察到干扰峰,从而发现了一种未知的代谢物。这种未知代谢物的分子量与母体药物相同,它们的碎片图谱也非常相似。对服用了 I 及其
氘标记类似物的狗和大鼠的血浆
提取物进行的 LC/MS/MS 分析表明,未知代谢物具有腈酮结构。合成的腈酮与未知代谢物具有相同的保留时间和几乎相同的碎片特征。腈酮在环境温度下的酸性
水溶液中缓慢分解,在电喷雾离子化质谱分析过程中也发生了源内热诱导
水解。腈酮与
乙炔二
甲酸二
乙酯的反应很容易生成[2 + 3]环加成产物。本例清楚地表明,在选择反应监测模式下进行 LC/MS/MS 定量时必须采取预防措施。