Combination of cyclodextrins and polymeric surfactants for chiral separations

A cyclodextrin‐modified micellar electrokinetic chromatography (CD‐MEKC) method was applied to the enantioseparation of three binaphthyl derivatives using neutral CDs (i.e., β‐ and γ‐CD) in combination with various chiral amino acid‐based polymeric surfactants (PSs). Both the D‐ and L‐configurations of poly(sodium N‐undecanoyl alaninate), poly(sodium N‐undecanoyl leucinate), and poly(sodium N‐undecanoyl valinate) (poly(L‐SUV)) were synthesized. The retention behavior of the three binaphthyl derivatives under optimum electrophoretic conditions using a single chiral additive (PS or CD) is discussed. In addition, the effect of CD cavity size and stereochemical configuration of polymeric surfactants on selectivity (α) and resolution (Rs) was investigated. The enantioseparation of (±)1,1'‐binaphthyl‐2,2'‐diamine gave a reversal of enantiomeric order when using β‐CD in combination with any of the three D‐configuration PS. However, better enantioseparation is obtained when using the corresponding L‐configuration PS with β‐CD. A reversal of migration order (RMO) for the enantiomers of (±)1,1'‐bi‐2‐naphthol was observed upon the addition of 10 mM γ‐CD to poly(L‐SUV). However, no RMO of (±)1,1'‐bi‐2‐naphthol was seen when either β‐CD or γ‐CD was combined with D‐PS. The enantiomers of (±)1,1'‐binaphthyl‐2,2'‐diyl hydrogen phosphate showed little enantioselective behavior toward the PS alone. However, combined D‐ or L‐PS and β‐CD or γ‐CD systems gave increased Rs and α values. The chiral recognition of binaphthyl derivatives observed resulting from the various combinations of two chiral selectors is discussed.