NMR Spectroscopic Analysis on the Chiral Recognition of Noradrenaline by β-Cyclodextrin ( β-CD) and Carboxymethyl- β-cyclodextrin (CM- β-CD)

${\beta}$-CD and CM- ${\beta}$-CD as chiral NMR shift agents were used to resolve the enantiomers of noradrenaline (NA). The stoichiometry of each complex formed between the CDs and the enantiomers of NA was found to be 1 : 1 through the continuous variation plots. The binding constants (K) of the complexes were determined from $^1H$ NMR titration curves. This result indicated that both ${\beta}$-CD and CM- ${\beta}$-CD formed the complexes with the S(+)-NA more preferentially than its R(-)-enantiomer. The K values for the complexes with ${\beta}$-CD ($K_{S(+)}$ = 537 $M^{-1}$ and $K_{R(-)}$ = 516 $M^{-1}$ was larger than those with CM- ${\beta}$-CD ($K_{S(+)}$ = 435 $M^{-1}$ and $K_{R(-)}$ = 313 $M^{-1}$), however, enantioselectivity (${\alpha}$) of S(+)- and R(-)-NA to CM- ${\beta}$-CD ( ${\alpha}$ = 1.38) was larger than that to ${\beta}$-CD ( ${\alpha}$ = 1.04), indicating that CM- ${\beta}$-CD was the better chiral NMR solvating agents for the recognition of the enantiomers of NA. Two dimensional rotating frame nuclear Overhauser enhancement spectroscopy (ROESY) experiments were also performed to explain the binding properties in terms of spatial fitting of the NA molecule into the macrocyclic cavities.