Freitag D G, Foster R T, Coutts R T, Pasutto F M
Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, Canada.
J Chromatogr. 1993 Jul 2;616(2):253-9. doi: 10.1016/0378-4347(93)80393-i.
(+/-)-Mexiletine is a class Ib antiarrhythmic drug useful in the treatment of premature ventricular contractions. It is predominantly metabolized by the liver with less than 15% being excreted in urine as unchanged drug. p-Hydroxymexiletine (PHM) and hydroxymethylmexiletine (HMM) are the two major mammalian metabolites. The purpose of our study was to develop a stereospecific high-performance liquid chromatographic (HPLC) method to determine whether the fungus, Cunninghamella echinulata (UAMH 4145), was able to biosynthesize these same two metabolites from the substrate (+/-)-mexiletine. Furthermore, it was desirable to ascertain whether metabolism of mexiletine was stereoselective. The method requires pre-column derivatization of the drug and metabolites with S-(+)-1-(1-naphthyl)ethyl isocyanate (NEIC) followed by normal-phase HPLC. Mexiletine, PHM, HMM and (+/-)-1-(4-hydroxyphenoxy)-3-isopropylaminopropan-2-ol (internal standard) were extracted from microbial broth using two volumes of diethyl ether after basifying with sodium carbonate. The combined ether extracts were evaporated to dryness, using a gentle stream of nitrogen, and reconstituted in 0.3 ml of chloroform to which was added 0.075 ml of NEIC (0.1%, v/v, in chloroform). This solution was immediately evaporated to dryness under a nitrogen stream. The residue was reconstituted with 0.220 ml of chloroform and 0.030 ml of n-butylamine (0.33%, v/v, in chloroform) and injected into the HPLC system.
（±）-美西律是一种I b类抗心律失常药物，可用于治疗室性早搏。它主要在肝脏代谢，以原形药物形式经尿液排泄的不到15%。对羟基美西律（PHM）和羟甲基美西律（HMM）是两种主要的哺乳动物代谢产物。我们研究的目的是开发一种立体特异性高效液相色谱（HPLC）方法，以确定真菌棘孢小克银汉霉（UAMH 4145）是否能够从底物（±）-美西律生物合成这两种相同的代谢产物。此外，还需要确定美西律的代谢是否具有立体选择性。该方法需要用S-（+）-1-（1-萘基）乙基异氰酸酯（NEIC）对药物和代谢产物进行柱前衍生，然后进行正相HPLC分析。用碳酸钠碱化后，用两体积的乙醚从微生物肉汤中提取美西律、PHM、HMM和（±）-1-（4-羟基苯氧基）-3-异丙氨基丙-2-醇（内标）。合并的乙醚提取物用温和的氮气流蒸发至干，然后用0.3 ml氯仿复溶，并加入0.075 ml NEIC（0.1%，v/v，氯仿溶液）。该溶液立即在氮气流下蒸发至干。残渣用0.220 ml氯仿和0.030 ml正丁胺（0.33%，v/v，氯仿溶液）复溶，并注入HPLC系统。
