Enantiomer Separation of Chiral Amines and Amino Acid Esters on Polysaccharide Phenylcarbamates Derived Chiral Stationary Phases

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We have developed an efficient chiral HPLC method for enantiomeric resolution of some chiral amines and α- amino acid esters as nitrobenzoxadiazole (NBD) derivatives on amylose and cellulose phenylcarbamates derived chiral stationary phases (CSPs) under simultaneous ultraviolet (UV) and fluorescence (FL) detection. The observed enantioselectivities were affected by the type of the analyte (amines or α-amino acid esters), backbone structure (cellulose or amylose) of the CSP used, and substituents of phenyl moiety on the chiral selector of CSP. Further, for same chiral selectors, coated type CSPs showed better enantiomeric separation than those observed for the covalently bonded type CSPs. In general, for the enantiomeric resolution of chiral amines, Chiralpak IE and Chiralcel OD-H columns showed the highest enantioselectivities. However, for resolution of α-amino acid esters, the performances of Chiralpak IA and Chiralpak AD-H (or Lux Amylose-1) columns were superior to those of other CSPs used. In general, the degrees of enantioselectivity for α-amino acid ethyl esters are greater than those for chiral amines. The developed analytical method was applied to determine the enantiomeric purity of two commercially available chiral amine and α-amino acid ester; the enantiomeric impurities were observed to be 0.35 and 0.05% for (S)-α-methylbenzylamine and (S)-leucine ethyl ester, respectively. The validation data obtained from intra- and inter-day accuracy assays for (S)-3,3-dimethyl-2-butylamine and (S)-leucine ethyl ester were 99.92-101.46 and 100.61-101.78%; and 100.05-102.12 and 101.25-102.73%, respectively; the intra- and interday precision assays in terms of relative standard deviation (% RSD) were found to be 0.96-1.57 and 0.81- 1.91%; and 0.24-1.01% and 0.65-1.35%, respectively. Owing to the high accuracy and precision results, the developed analytical method can prove to be useful for the enantiomeric separation of various chiral amines and amino acid esters as NBD derivatives using polysaccharide derived CSPs.