g Yu Jin

Liquid Chromatographic Enantiomer Separation of N‐Phthaloyl Protected α‐Amino Acids on Coated and Immobilized Chiral Stationary Phases Derived from Polysaccharide Derivatives

Abstract Liquid chromatographic enantiomer separation of N‐phthaloyl (PHT) protected α‐amino acids on several coated and immobilized chiral stationary phases (CSPs) derived from polysaccharide derivatives was performed. The coated CSP of Chiralpak AD showed more or less enantioseparation than the covalently bonded CSP of Chiralpak IA with the same chiral selector of amylose tris(3,5‐dimethylphenylcarbamate). However, the coated Chiralcel OD showed greater enantioseparation than the covalently bonded Chiralpak IB with the same chiral selector of cellulose tris(3,5‐dimethylphenylcarbamate). Among all examined CSPs, Chiralcel OD afforded the greatest performance for enantiomer resolution of N‐PHT α‐amino acids and, therefore, all analytes enantiomers were baseline separated on Chiralcel OD. The chromatographic method developed in this study was usefully applied for determination of the enantiomeric purity of commercially available N‐PHT α‐amino acids analytes.

Development of the Antipode of the Covalently Bonded Crown Ether Type Chiral Stationary Phase for the Advantage of the Reversal of Elution Order

Abstract Chiral stationary phases, CSP 1 and CSP 2, with a reverse stereochemical configuration, were prepared by covalently bonding (+)‐ and (−)‐(18‐crown‐6)‐2,3,11,12‐tetracarboxylic acid (18‐C‐6‐TA) to silica gel, respectively. These CSPs were used to resolve the enantiomers of α‐amino acids and primary amino compounds, affording reasonable and quite similar resolution behaviors except for the elution orders. The elution orders of the two enantiomers for the resolution of α‐amino acids and other primary amino compounds were always opposite on the two CSPs. The reverse elution orders on the two CSPs with the antipode of the chiral selector were demonstrated to be very useful in the determination of the enantiomeric purity of optically enriched analytes.

Comparative studies between covalently immobilized and coated chiral stationary phases based on polysaccharide derivatives for enantiomer separation of N‐protected α‐amino acids and their ester derivatives

Liquid chromatographic enantiomer separation of several N-benzyloxycarbonyl (CBZ) and N-tert-butoxycarbonyl (BOC) alpha-amino acids and their corresponding ethyl esters was performed on covalently immobilized chiral stationary phases (CSPs) (Chiralpak IA and Chiralpak IB) and coated-type CSPs (Chiralpak AD and Chiralcel OD) based on polysaccharide derivatives. The solvent versatility of the covalently immobilized CSPs in enantiomer separation of N-CBZ and BOC-alpha-amino acids and their ester derivatives was shown and the chromatographic parameters of their enantioselectivities and resolution factors were greatly influenced by the nature of the mobile phase. In general, standard mobile phases using 2-propanol and hexane on Chiralpak IA showed fairly good enantioselectivities for resolution of N-CBZ and BOC-alpha-amino acids and their esters. However, 50% MTBE/hexane (v/v) for resolution of N-CBZ-alpha-amino acids ethyl esters and 20% THF/hexane (v/v) for resolution of N-BOC-alpha-amino acids ethyl esters afforded the greatest enantioselectivities on Chiralpak IA. Also, liquid chromatographic comparisons of the enantiomer resolution of these analytes were made on amylose tris(3,5-dimethylphenylcarbamate)-derived CSPs (Chiralpak IA and Chiralpak AD) and cellulose tris(3,5-dimethylphenylcarbamate)-derived CSPs (Chiralpak IB and Chiralcel OD). Chiralpak AD and/or Chiralcel OD showed the highest enantioselectivities for resolution of N-CBZ-alpha-amino acids and esters, while Chiralpak AD or Chiralpak IA showed the highest resolution of N-BOC-alpha-amino acids and esters.

Covalently Bonded and Coated Chiral Stationary Phases Derived from Polysaccharide Derivatives for Enantiomer Separation of N‐Fluorenylmethoxycarbonyl α‐Amino Acids with Fluorescence Detection

Abstract Liquid chromatographic comparisons for enantiomer resolution of N‐fluorenylmethoxycarbonyl (FMOC) α‐amino acids with fluorescence detection were made on covalently bonded type chiral stationary phases (CSPs) (Chiralpak IA and Chiralpak IB) and coated type CSPs (Chiralpak AD and Chiralcel OD) derived from polysaccharide derivatives of the same chiral selectors. This is the first study reported of enantiomer resolution with fluorescence detection on covalently bonded type CSPs, Chiralpak IA and Chiralpak IB. In general, covalently bonded type CSPs (Chiralpak IA and Chiralpak IB) showed lower enantioseparation than coated type CSPs (Chiralpak AD and Chiralcel OD) for enantiomer resolution of these analytes, respectively. Owing to higher sensitivity and broader solvent compatibility in fluorescence detection on Chiralpak IA and Chiralpak IB than in UV detection, however, this analytical method is expected to enlarge their application of enantiomer resolution, such as an online HPLC monitoring of asymmetric synthesis.

LIQUID CHROMATOGRAPHIC ENANTIOMER SEPARATION OF AMINO ACID ESTERS AS 9-ANTHRALDIMINE SCHIFF BASES USING POLYSACCHARIDE-DERIVED CHIRAL STATIONARY PHASES

The liquid chromatographic enantiomer separation of several amino acid methyl esters as 9-anthraldehyde Schiff base derivatives on coating and covalently bonded polysaccharide-derived chiral stationary phases (CSPs) is described. The 9-anthraldehyde imine derivatives of amino acid esters were readily prepared by stirring 9-anthraldehyde with the amino acid ester hydrochloride salts. The performance of Chiralcel OD among all examined CSPs was superior to that of the other CSPs for resolution of 9-anthraldimine derivatives of amino acid methyl esters. The enantiomers of all examined amino acid methyl esters as the 9-anthraldimine derivatives were base-line resolved on Chiralcel OD. The L-enantiomers of all analytes are preferentially retained on Chiralcel OD. The chromatographic methods developed in this study were applied in the determination of enantiomeric purity of some commercially available D- or L-amino acid methyl esters.

Comparison of several polysaccharide-derived chiral stationary phases for the enantiomer separation ofN-fluorenylmethoxy-carbonyl α-amino acids by hplc

The liquid chromatographic enantiomer separation ofN-fluorenylmethoxycarbonyl (FMOC) protected α-amino acids was performed on nine polysaccharide-derived chiral stationary phases (CSPs). The cellulose derived coated CSPs, Chiralcel OD-H (separation factor = 1.09– 2.70) and Chiralcel OD (separation factor = 1.08–2.55), had the best performance of all the CSPs for resolution ofN-FMOC α-amino acids and therefore, all analyte enantiomers were base-line separated on Chiralcel OD-H and/or Chiralcel OD. Enantioseparation on cellulose tris(3,5-dimethylphenylcarbamate) derived CSPs (Chiralcel OD-H, Chiralcel OD and Chiralpak IB) is generally greater than that on amylose tris(3,5-dimethylphenylcarbamate) derived CSPs (Chiralpak AD-RH, Chiralpak AD and Chiralpak IA). Additionally, coated type CSPs (Chiralcel OD-H or Chiralcel OD, and Chiralpak AD) generally provided better enantioseparation for these analytes than the covalently bonded type CSPs (Chiralpak IB and Chiralpak IA) with the same chiral selector of cellulose tris(3,5-dimethylphenylcarbamate) and amylose tris(3,5-dimethylphenylcarbamate), respectively. However, Chiralpak IB and Chiralpak IA had an advantage over the coated type CSPs in that a broader range of solvents could be used due to its covalently bonded nature.