Chiral Separation of Apremilast by Capillary Electrophoresis Using Succinyl-ß-Cyclodextrin-Reversal of Enantiomer Elution Order by Cationic Capillary Coating.

A stereospecific capillary electrophoresis method was developed for the separation of the novel, antipsoriatic agent, apremilast (APR). Six anionic cyclodextrin (CD) derivatives were screened for their ability to discriminate between the uncharged enantiomers. Only succinyl-ß-CD (Succ-ß-CD) presented chiral interactions; however, the enantiomer migration order (EMO) was unfavorable, and the eutomer, S-APR, migrated faster. Despite the optimization of all possible parameters (pH, cyclodextrin concentration, temperature, and degree of substitution of CD), the method was unsuccessful for purity control due to the low resolution and the unfavorable enantiomer migration order. Changing the direction of electroosmotic flow (EOF) by the dynamic coating of the inner surface of the capillary with poly(diallyldimethylammonium) chloride or polybrene resulted in EMO reversal, and the developed method could be applied for the determination of R-APR as the enantiomeric purity. Thus, the application of the dynamic capillary coating offers a general opportunity for enantiomeric migration order reversal in particular cases when the chiral selector is a weak acid.

Simultaneous Determination of Escitalopram Impurities including the R-enantiomer on a Cellulose tris(3,5-Dimethylphenylcarbamate)-Based Chiral Column in Reversed-Phase Mode.

A high-performance liquid chromatographic method was developed for the simultaneous determination of the related substances-three potential synthesis-related chemical impurities and the distomer-of escitalopram. The separation capacity of seven different polysaccharide-type chiral columns, including three amylose-based (Lux Amylose-1, Lux i-Amylose-1, Lux Amylose-2) and four cellulose-based columns (Lux Cellulose-1, Lux Cellulose-2, Lux Cellulose-3, and Lux Cellulose-4) were screened in the polar organic and reversed-phase modes. Lux Cellulose-1, based on cellulose tris(3,5-dimethylphenylcarbamate) as the chiral selector with an acetonitrile-water mixture containing 0.1% diethylamine was identified as the most promising separation system. Using the "one factor at a time" optimization approach, the effect of column temperature, flow rate, and mobile phase constituents on separation performance was evaluated, and the critical resolution values were determined. A U-shaped retention pattern was obtained when plotting the retention factors of the citalopram enantiomers versus the water content of the binary mobile phases on the Lux Cellulose-1 column. A thermodynamic analysis revealed enthalpy-driven enantioseparation in both the polar organic and reversed-phase modes. For further method optimizations, an L9 orthogonal array table was employed. Using the optimized parameters (Lux Cellulose-1 column with 0.1% (v/v) diethylamine in water/acetonitrile 55/45 (v/v); 0.8 mL/min flow rate at 25 °C), baseline separations were achieved between all compounds. Our newly developed HPLC method was validated according to the ICH guidelines and its application was tested with a commercially available pharmaceutical formulation. The method proved to be suitable for routine quality control of related substances and the enantiomeric purity of escitalopram.

Liquid chromatographic method for the simultaneous determination of achiral and chiral impurities of dapoxetine in approved and counterfeit products.

A reversed-phase high performance liquid chromatographic method was developed and validated for the simultaneous determination of the related substances of S-dapoxetine, including R-dapoxetine, (3S)-3-(dimethylamino-3-phenyl-1-propanol), S-3-amino-3-phenyl-1-propanol, 1-naphtol, 4-phenyl-2H,3H,4H-naphtho[1,2-b]pyran and 1-(2E)-Cinnamyloxynaphthalene. During the screening experiments seven different polysaccharide-type chiral stationary phases (amylose-based Lux-Amylose-1, Lux-i-Amylose-1 and Lux-Amylose-2, as well as cellulose-based Lux-Cellulose-1, Lux-Cellulose-2, Lux-Cellulose-3 and Lux-Cellulose-4) were tested in polar organic mode using a mobile phase consisting of 0.1% diethylamine in methanol, ethanol, 2-propanol and acetonitrile with 0.5 mL min-1 flow rate at 20 °C. Best results were obtained on Lux Cellulose-3 column with the ethanol-based mobile phase. To increase the retention factor of two, early-eluting impurities, water was added to the mobile phase. In order to counterbalance the increased total analysis time, higher column temperature (40 °C) and gradient elution, combined with flow-programming` was applied. Using the optimized conditions baseline separations were achieved for all compounds within 30 min. The method was validated according to the International Council on Harmonization guideline Q2(R1) and applied to the analysis of an approved, tablet formulation and dapoxetine-containing products sold on the internet. As expected, in the case of the pharmacy-acquired product, all of the monitored impurities were below 0.1%. However, interesting results were obtained when internet-acquired samples were analyzed. These tablets contained racemic dapoxetine and/or high concentration of R-dapoxetine impurity. Based on this work polysaccharide-based chiral stationary phases can be successfully applied for the simultaneous determination of achiral and chiral impurities in reversed-phase mode applying gradient elution and flow-rate programs. The study further underlines the importance of not only achiral, but also enantiomeric quality control, whenever counterfeiting of a single enantiomeric agent is suspected.