Chiral separation of several naphthalenesulfonylamino acids by capillary zone electrophoresis with selectively methylated cyclodextrin derivatives

The chiral separation of six pairs of alpha- and beta-naphthalenesulfonylamino acid enantiomers was examined by capillary zone electrophoresis using selectively methylated beta-cyclodextrin (beta-CD) and gamma-cyclodextrin (gamma-CD) derivatives as chiral selectors. On the whole, the gamma-CD derivatives exhibited higher enantioselectivities than the beta-CD derivatives. Unmodified gamma-CD and the gamma-CD derivative whose 6-hydroxyl groups were methylated (6-monomethylated gamma-CD) exhibited similar high enantioselectivities. After methylation of the hydroxyl groups at the 3-position of the unmodified and 6-monomethylated gamma-CDs, their chiral recognition ability for beta-naphthalenesulfonylamino acids was drastically enhanced. Methylation of both the 2- and 3-positions of gamma-CD resulted in the complete disappearance of the enantioselectivity regardless of 6-monomethylation. In addition, both beta- and gamma-CD derivatives showed different enantioselectivities for alpha-naphthalenesulfonylamino acids from those for beta-naphthalenesulfonyl amino acids, especially remarkable in the case of unmodified and 6-monomethylated CDs. Using H-1-NMR measurements, it was confirmed that the naphthyl group of alpha-naphthalenesulfonyl-DL-leucine penetrated more deeply into the gamma-CD cavity than into that of beta-CD and that the naphthyl group of beta-naphthalenesulfonyl-DL-leucine penetrated more deeply into the beta-CD cavity than that of alpha-naphthalenesulfonyl-DL-leucine. (C) 1997 Elsevier Science B.V.