Nucleophilic substitution of (sulfonyloxymethyl)aziridines: an asymmetric synthesis of both isomers of mexiletine

Enantioselective Analysis of Mexiletine Using Chromatographic Techniques: A Review

Background:

Mexiletine belongs to the β-amino-aryl-ether group of pharmaceutical and applied in the diagnosis of antiarrhythmics, allodynia, and myotonic disorders. In its chemical structure, it possesses a chiral center and practiced in the form of the racemic mixture. The production and accessibility of mexiletine have accompanied with a meaningful development in awareness of its pharmacologic actions. But in clinical arrhythmias and binding experiments on cardiac sodium channels, the (R)-enantiomer of mexiletine is more potent than the (S)-enantiomer. Also, (S)-enantiomer is further active in the diagnosis of allodynia than the (R)-enantiomer.

Methods:

During the last two decades, chromatographic techniques such as HPLC, and GC coupled with mass spectrometry or field ionization detector was used for the stereoselective analysis of MEX enantiomers.

Results:

The direct enantioresolution deal with the use of chiral stationary phases (CSPs) with or no pre-derivatization which depend on a chromophoric entity in the racemates whereas indirect HPLC process involved the use of chiral derivatization reagents (CDR) for the synthesis of diastereomeric derivatives of racemates. Different techniques have their strengths and weaknesses.

Conclusion:

Regulation of enantiomeric purity and estimation of particular enantiomers of drug molecules stays an essential topic for therapeutic, diagnostic, and regulatory uses and to promote a precise assessment of the hazards to human health by false enantiomers. This review aims to offer a systematic survey of the analytical methods (chromatography based) used in the enantioselective analysis of MEX developed in the last two decades (the year 2000 onwards).

Enantiodivergent syntheses of (+)- and (-)-1-(2,6-dimethylphenoxy)propan-2-ol: A way to access (+)- and (-)-mexiletine from D-(+)-mannitol

Chiron approach was used to acquire optically pure (R)- and (S)-1-(2,6-dimethylphenoxy)propan-2-ol, immediate precursors of (S)- and (R)-mexiletines, respectively. Two different routes were followed from a D-mannitol-derived optically pure common precursor to get the enantiomeric alcohols separately. Comparison of their specific rotation values with the corresponding literature values as well as exact mirror-image relationship between their CD curves proved their high enantiopurity. These alcohols were then transformed to the corresponding amine-drugs in an efficient one-step process instead of two steps described in the literature.

N-(1-Phenylethyl)aziridine-2-carboxylate esters in the synthesis of biologically relevant compounds

Since Garner’s aldehyde has several drawbacks, first of all is prone to racemization, alternative three-carbon chirons would be of great value in enantioselective syntheses of natural compounds and/or drugs. This review article summarizes applications of N-(1-phenylethyl)aziridine-2-carboxylates, -carbaldehydes and -methanols in syntheses of approved drugs and potential medications as well as of natural products mostly alkaloids but also sphingoids and ceramides and their 1- and 3-deoxy analogues and several hydroxy amino acids and their precursors. Designed strategies provided new procedures to several drugs and alternative approaches to natural products and proved efficiency of a 2-substituted N-(1-phenylethyl)aziridine framework as chiron bearing a chiral auxiliary.

Preparation of Chiral Contiguous Epoxyaziridines and Their Regioselective Ring-Opening for Drug Syntheses

Synthetically valuable chiral (aziridin-2-yl)oxirane-3-carbaldehydes bearing three consecutive functional groups including aziridine, epoxide, and aldehyde were prepared from the stereoselective epoxidation of (aziridin-2-yl)acrylaldehydes with H₂ O₂ using organocatalyst (2R)- or (2S)-[diphenyl(trimethylsilyloxy)methyl]pyrrolidine as organocatalyst. The regioselective ring opening of aziridines and epoxides enabled us to achieve the highly efficient asymmetric synthesis of the antibiotic edeine D fragment 3-hydroxy-4,5-diaminopenatanoic acid, an intermediate for the formal synthesis of non-proteinogenic amino acid (-)-galantinic acid, and for potent antifungal agent (+)-preussin, and the medicinally important framework 3-hydroxy-2-hydroxymethylpyrrolidine.