Direct enantioselective HPLC monitoring of lipase‐catalyzed kinetic resolution of tiaprofenic acid in nonstandard HPLC organic solvents

Abstract

The first straightforward lipase-catalyzed enantioselective access to enantiomerically enriched tiaprofenic acid as a versatile method in chiral separation of racemates is demonstrated. The latter was directly monitored by enantioselective HPLC using a 3,5-dimethylphenylcarbamate derivative of cellulose-based chiral stationary phase namely Chiralpak IB (the immobilized version of Chiralcel OD). Non-standard HPLC organic solvents were used as diluent to dissolve the "difficult to dissolve" enzyme substrate (the acid) and as eluent for the simultaneous enantioselective HPLC baseline separation of both substrate and product in one run without any further derivatization. The existence of a non-standard HPLC organic solvent (e.g., methyl tert-butyl ether) in the mobile phase composition is mandatory to accomplish the simultaneous enantioselective HPLC baseline separation of both substrate and product.

Direct enantioselective HPLC monitoring of lipase‐catalyzed kinetic resolution of flurbiprofen

“…These simultaneous baseline separations in one run is mandatory for the precise determination of the enantiomeric excesses of substrates and products. The latter is an important prerequisite for the detailed investigation of the enzyme‐catalyzed enantioselective resolution of racemates 19, 20…”

“…While in toluene (log P 2.50) Novozym525 showed very good enantioselectivity and enantiomeric excess of unreacted substrate (ee s ) (S‐acid) at maximum conversion (54.0%), in shorter time (ee s = 96.1 %, ee p = 81.8 %, E = 39.0 after 16 hrs). Log P in Table 2 is defined as the ratio of concentration of a substance in two immiscible phases at equilibrium namely octanol and water and used to describe the correlation of hydrophobicity and the enantioselectivity E of lipases 19…”

“…Lipase‐catalyzed kinetic resolution of flurbiprofen in nonstandard HPLC solvents such as dichloromethane (DCM), ethyl acetate (EtOAc), methyl tert ‐butyl ether (M t BE) and tetrahydrofuran (THF) might be the method of choice to overcome solubility problem of the substrate 19. However, such nonstandard solvents might cause irreversible damage of the CSP by dissolving or swelling of the chiral selector 20–22.…”

“…Such immobilization renders the polysaccharide derivatives insoluble in any mobile phase solvent21, 22 and combines the benefits of the coated polysaccharide‐type CSPs namely the broad application scope and the high preparative potential‐ with enhanced robustness, practically unlimited solvent compatibility and extended range of applications 21–24. Subsequently, broadening the choice of solvents able to be used as mobile phase eluent or diluents 19, 20…”

Analysis of Stiripentol Enantiomers on Several Chiral Stationary Phases: A Comparative Study

“…In recent reports, direct analysis has been reported where simultaneous baseline chiral HPLC separation of stiripentol and its acetate, propanoate and butanoate esters in one run with n-Hexane, 2-propanol (2-PrOH) and methyl tert-butyl ether (MtBE) as mobile phase components at different ratios on Chiralcel OD-H column with the aim to follow up biocatalyzed reactions [7,8]. It is well known that derivatization of enantiomers in order to estimate its purity could lead to racemization and/or partial or complete enantiomeric fractionation [9,10]. However, all pharmacological and pharmacokinetic studies on stiripentol have been performed using the indirect HPLC method.…”