Freitag DG, Foster RT, Coutts RT, Pasutto FM. High-performance liquid chromatographic method for resolving the enantiomers of mexiletine and two major metabolites isolated from microbial fermentation media.
JOURNAL OF CHROMATOGRAPHY 1993;
616:253-9. [PMID:
8376507 DOI:
10.1016/0378-4347(93)80393-i]
[Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
(+/-)-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.
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