Enantiomeric recognition of amino acid ester salts by β-cyclodextrin derivatives: an experimental and computational study

beta-cyclodextrin derivatives bearing benzoyl (beta-CD-1) and naphthoyl beta-CD-2) moieties have been synthesized from salicylic acid and 3-hydroxy-2-naphthoic acid by a convenient method in 60% and 58% yields, respectively, and were tested for enantiomeric recognition of amino acid ester derivatives. Their ability to discriminate between various L-/D-amino acid methyl ester hydrochloride salts was examined using the H-1 NMR titration method in DMSO-d(6) at 25 degrees C. beta-CD- 2 produced a fairly good discrimination of tryptophan ester salts with a binding constant of 4041 M-1 for L-salt compared with 2864 M-1 for D-salt, which corresponds to a difference of 0.21 kcal mol(-1) in binding free energies. The binding free energies obtained from molecular dynamic calculation by MM/PB(GB) SA are consistent with those obtained from the experimental results.