Chiral interconversion monitoring of a drug candidate by supercritical fluid chromatography (SFC)

Enantioselective polar-organic mode high-performance liquid chromatographic separation of lifitegrast on immobilized polysaccharide stationary phase and its application to pH-dependent chiral interconversion studies

(S)-Lifitegrast (LFT) is the novel integrin antagonist, approved by the Food and drug administration, to treat signs and symptoms of dry eye disease. Synthesis of racemic LFT, preparative and analytical enantiomer separation, and chiral interconversion studies are lacking in the literature. Hence, in our study, synthesis of LFT racemate, chiral preparative purification procedure of enantiomer, and comprehensive analytical advancements are focused on rapid enantioselective separation and pH-dependent chiral interconversion studies. The synthesis of LFT racemate employed 2-amino-3-(3-(methylsulfonyl)phenyl)propanoic acid hydrochloride and 2-(benzofuran-6-carbonyl)-5,7-dichloro-1,2,3,4-tetrahydroisoquinoline-6-carbonyl chloride as starting materials. (R)-LFT was isolated from the racemate by preparative chiral HPLC and characterized using Q-TOF, FT-IR, NMR spectroscopy, and chiral HPLC. The purity of (R)-LFT was determined to have an enantiomeric excess of 99.12%. A precise, accurate, rapid HPLC-DAD enantioselective analytical method has been developed on Chiralpak IC [tris(3,5-dichloro phenyl carbamate) immobilized on cellulose] using water and methanol as mobile phase. The chiral interconversion study reveals 0.22% and 0.21% of interconversion of (S)-LFT into (R)-LFT at 80°C in pH 7.4 and 9.5 buffers, respectively, on the 24th day. An alternative route to enantioselective synthesis of LFT enantiomers by chromatographic separation is proposed. The validated enantioselective HPLC method will help to test the regular quality control samples.

Racemisation in Chemistry and Biology

The two enantiomers of a compound often have profoundly different biological properties and thus their liability to racemisation in aqueous solutions is an important piece of information. The authors reviewed the available data concerning the process of racemisation in vivo, in the presence of biological molecules (e.g., racemase enzymes, serum albumin, cofactors and derivatives) and under purely chemical but aqueous conditions (acid, base and other aqueous systems). Mechanistic studies are described critically in light of reported kinetic data. The types of experimental measurement that can be used to effectively determine rate constants of racemisation in various conditions are discussed and the data they provide is summarised. The proposed origins of enzymatic racemisation are presented and suggest ways to promote the process that are different from processes taking place in bulk water. Experimental and computational studies that provide understanding and quantitative predictions of racemisation risk are also presented.

Study on the racemization of synephrine by off-column chiral high-performance liquid chromatography

In this study, the racemization kinetic parameters of R-(-)-synephrine, the active phenethylamine alkaloid of Citrus aurantium L., were determined by means of an off-column HPLC method. Enantioseparation was carried out in different buffer solutions and solvents on a chiral stationary phase (CSP) with cellobiohydrolase as the chiral selector (Chiral-CBH, 100 mm x 4.0 mm i.d., 5 microm). The mobile phase was 10 mM sodium phosphate buffer (pH 6.0)-2-propanol (95:5, w/w), with 50 microM disodium EDTA, at 0.8 mL/min. The column was thermostatted at 20 degrees C and detection was set at 225 nm. The influence of pH value, ionic strength, temperature and addition of organic modifier on the rate constant, the half-life of racemization and the free energy barrier of racemization of R-(-)-synephrine were determined. Among the different chemical and physical parameters evaluated as affecting the racemization of naturally occurring R-(-)-synephrine, pH, temperature and addition of an organic co-solvent appear to have the strongest effect, while ionic strength does not exert a significant influence on the racemization rate. The results of the present study indicated that synephrine racemization is possible at high temperature at both acidic and basic pH values; therefore, the extraction procedure of R-(-)-synephrine from the plant material should be carried out under specific conditions to preserve the stereochemical integrity and the biological activity of this secondary metabolite.