CHIRAL MOLECULAR RECOGNITION - A F-19 NUCLEAR-MAGNETIC-RESONANCE STUDY OF THE DIASTEREOISOMER INCLUSION COMPLEXES FORMED BETWEEN FLUORINATED AMINO-ACID DERIVATIVES AND ALPHA-CYCLODEXTRIN IN AQUEOUS-SOLUTION

A F-19 NMR spectroscopic study (282.35 MHz) of the formation of diastereoisomeric inclusion complexes by fluorinated amino acid derivatives and alpha-cyclodextrin (alpha-CD) in 10% aqueous D2O solution yields the apparent stability constants K(R) and K(s)/dm3 mol-1 = 7.7 +/- 0.3 and 8.2 +/- 0.3 for protonated alpha-(p-fluorophenyl)glycine (1 + H), 21.5 +/- 0.4 and 22.5 +/- 0.4 for deprotonated alpha - (p-fluorophenyl)glycine (1 - H), 14.4 +/- 0.1 and 14.6 +/- 0.1 for N-acetyl-alpha-(p-fluorophenyl)glycine (2), 13.1 +/- 0.5 and 14.1 +/- 0.5 for deprotonated N-acetyl-alpha-(p-fluorophenyl)-glycine (2 - H), and 12.4 +/- 0.3 and 10.6 +/- 0.4 for deprotonated N-(p-fluorobenzoyl)valine (3 - H), where the first and second of each pair of values refers to the diastereoisomer formed between alpha-CD and the R and S enantiomer, respectively. The chemical shifts of the R-amino acid derivative . alpha-CD inclusion complexes are upfield from those of their S analogues for deprotonated N-(p-fluorobenzoyl)valine (3 - H), deprotonated alpha-(p-fluorophenyl) glycine (1 - H), and deprotonated N-acetyl-alpha-(p-fluorophenyl)glycine (2 - H), but this relationship is reversed for protonated alpha-(p-fluorophenyl)glycine (1 + H) and N-acetyl-alpha-(p-fluorophenyl)glycine (2 + H). In the case of the N-(p-fluorobenzoyl)valine . alpha-CD inclusion complex (3 . alpha-CD) the chemical shift difference between the diastereoisomers formed with the R and S enantiomers is too small for quantitative analysis and accordingly a composite K(R,S)/dm3 mol-1 = 8.3 +/- 0.3 was determined. The factors causing the variations in apparent stability constants and chemical shifts are discussed.