Development and validation of a chiral LC-MS method for the enantiomeric resolution of (+) and (-)-medetomidine in equine plasma by using polysaccharide-based chiral stationary phases

The preparation of optically active epineoclausenamide and enantiomeric separation of its racemate

We synthesized the optically active epineoclausenamide by utilizing chiral reagents, such as R-α-methylbenzylamine and S-α-methylbenzylamine, for the resolution of the intermediate (trans-3-phenyl-oxiranecarboxylic acid 12), followed by amide exchange, cyclization, and reduction, unlike previously reported methods. The Meerwein-Ponndorf-Verley reduction was used to asymmetrically reduce neoclausenamidone. A plausible reduction mechanism of this method was elucidated. Thereafter, high-performance liquid chromatography (HPLC) was investigated for the resolution of the epineoclausenamide enantiomers. HPLC was also used to determine the optical purity of these isomers. Two chiral stationary phases (CSPs) for separating the enantiomers were compared. Different mobile phase compositions were tested at 298.15 K. The results showed that the best separation was obtained when the mobile phase was composed of n-hexane and isopropanol (IPA) (75/25, v/v), the racemate was separated on a Chiralcel OJ-H column, and the flow rate was 1.0 mL/min at a wavelength of 210 nm and a temperature of 25°C. The enantiomeric ratio (e.r.) values of both the synthetic (-)-epineoclausenamide and (+)-epineoclausenamide were 1.3(+):98.7(-) and 99.3(+):0.7(-), respectively. In this study, a new synthetic route was designed with a yield of 12.3-14.1%, and a quick (8 min) effective separation method was obtained. This provides basis for pharmacological research and quality control of clausenamide analogues.

Polysaccharide- and β-Cyclodextrin-Based Chiral Selectors for Enantiomer Resolution: Recent Developments and Applications

Polysaccharides, oligosaccharides, and their derivatives, particularly of amylose, cellulose, chitosan, and β-cyclodextrin, are well-known chiral selectors (CSs) of chiral stationary phases (CSPs) in chromatography, because they can separate a wide range of enantiomers. Typically, such CSPs are prepared by physically coating, or chemically immobilizing the polysaccharide and β-cyclodextrin derivatives onto inert silica gel carriers as chromatographic support. Over the past few years, new chiral selectors have been introduced, and progressive methods to prepare CSPs have been exploited. Also, chiral recognition mechanisms, which play a crucial role in the investigation of chiral separations, have been better elucidated. Further insights into the broad functional performance of commercially available chiral column materials and/or the respective newly developed chiral phase materials on enantiomeric separation (ES) have been gained. This review summarizes the recent developments in CSs, CSP preparation, chiral recognition mechanisms, and enantiomeric separation methods, based on polysaccharides and β-cyclodextrins as CSs, with a focus on the years 2019-2020 of this rapidly developing field.

A quick approach for medetomidine enantiomer determination in dog plasma by chiral liquid chromatography-tandem mass spectrometry and application to a pharmacokinetic study

In the present study, a rapid, sensitive and high-throughput liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the determination of medetomidine enantiomers in dog plasma was developed and validated. The separation and individual quantification of chiral compounds can be a tricky task in LC. This is particularly true when target analytes have a relatively small mass, as is the case with medetomidine, a potent and highly specific α2-adrenoceptor agonist widely used in both human and veterinary medicine. The proposed approach is based on a quick liquid-liquid extraction with ethyl acetate and filtration prior to injection. The optimized mobile phase composition allowed to perfectly separate the two enantiomers of medetomidine in a short chromatographic run time, using a cellulose tris(4-methylbenzoate)-based chiral column. A lower limit of quantification of 0.1 ng/mL was reached for both analytes thanks to the high sensitivity and selectivity of MS/MS and the use of racemic medetomidine-d3 as internal standard prevented potential matrix effect. Linearity was satisfying (R²  > 0.99) over the range 0.1-25 ng/mL, as well as within- and between-session accuracy and precision, both always <15%. This method was also applied with success to a series of samples from a pharmacokinetic (PK) study aimed at comparing dex- and levomedetomidine behaviour after administration of the racemic mixture in dogs. The simple extraction procedure, which allows reduced solvent and time consumption without compromising analytical performances, makes this technique a useful tool for this kind of applications even when small animals are involved, due to the small amount of sample required.

Chiral chromatography method screening strategies: Past, present and future

Method screening is an integral part of chromatographic method development for the separation of racemates. Due to the highly complex retention mechanism of a chiral stationary-phase, it is often difficult, if not impossible, to device predefined method-development steps that can be successfully applied to a wide group of molecules. The standard approach is to evaluate or screen a series of stationary and mobile-phase combinations to increase the chances of detecting a suitable separation condition. Such a process is often the rate-limiting step for high-throughput analyses and purification workflows. To address the problem, several solutions and strategies have been proposed over the years for reduction of net method-screening time. Some of the strategies have been adopted in practice while others remained confined in the literature. The main objective of this review is to revisit, critically discuss and compile the solutions published over the last two decades. We expect that making the diverse set of solutions available in a single document will help assessing the adequacy of existing screening protocols in laboratories conducting chiral separation.