Chiral recognition ability and solvent versatility of bonded amylose tris(3,5-dimethylphenylcarbamate) chiral stationary phase: Enantioselective liquid chromatographic resolution of racemic N-alkylated barbiturates and thalidomide analogs

The chiral recognition ability and solvent versatility of a new chiral stationary phase containing amylose 3,5-dimethylphenylcarabamate immobilized onto silica gel (CHIRALPAK® IA) is investigated. Thus, the direct enantioselective separation of a set of racemic N-alkylated barbiturates and 3-alkylated analogs of thalidomide was conducted using different nonstandard solvents as eluent and diluent, respectively in high-performance liquid chromatography (HPLC). The separation, resolution, and elution order of the investigated compounds were compared on both immobilized and coated amylose tris(3,5-dimethylphenylcarbamate) chiral stationary phases (Chiralpak IA and Chiralpak AD, respectively) using a mixture of n-hexane/2-propanol (90:10 v/v) as mobile phase with different flow-rates and fixed UV detection at 254 nm. The effect of the immobilization of the amylose tris(3,5-dimethylphenylcarbamate) chiral stationary phase on silica (Chiralpak IA) on the chiral recognition ability was noted as the bonded phase (Chiralpak IA) was superior in chiral recognition and possesses a higher resolving power in most of the reported cases than the coated one (Chiralpak AD). A few racemates were not or poorly resolved on the immobilized Chiralpak IA or the coated Chiralpak AD when using standard solvents were most efficiently resolved on the immobilized Chiralpak IA upon using nonstandard solvents. Furthermore, the immobilized phase withstands the nonstandard (prohibited) HPLC solvents such as dichloromethane, ethyl acetate, tetrahydrofuran, methyl-tert-butyl ether, and others when used as eluents or as a dissolving agent for the analyte itself. The direct analysis of a real sample extracted from plasma using DCM on Chiralpak IA is also shown.