Retention behavior and chiral recognition mechanism of several cyclodextrin-bonded stationary phases for dansyl amino acids

Abstract

Five types of natural and chemically modified ßor 7-cyclodextrln-bonded stationary phases have been prepared and their ability to separate enantiomers of 12 dansyl amino acids was Investigated by using phosphate buffer containing methanol as mobile phases. Effects of methanol content, Ionic strength, and pH of the mobile phase on retention and chiral selectivity of the analytes on each stationary phase are examined to optimize the mobile phase conditions. The elution orders of each pair of enantiomer of all dansyl amino acids on natural ß-and 7-CD-bonded stationary phases as well as on two modified /3-CD-bonded stationary phases were l < d enantiomer, while a reverse elution order was observed for dansyl-D,L-Trp and dansyl-D,L-Phe only on 6-0-phenylcarbamoylated 7-CD-bonded stationary phase. Among these stationary phases, 7-cyclodextrln-bonded stationary phase exhibited the highest resolution to not only enantiomers but homologues. A chiral recognition mechanism Is also proposed based on the competitive Inclusion model which involves the formation of an Inclusion complex of cyclodextrin with a dansyl group as well as with a side chain on an asymmetric carbon atom of dansyl amino acids.

Chiral separation of enantiomers of amino acid derivatives by high-performance liquid chromatography on a norvancomycin-bonded chiral stationary phase

“…The reason may be that the resistance Table 1 The thermodynamic parameters of the enantioseparation of four dansyl-amino acids with a mobile phase composition of acetonitrile/TEAA buffer = 1/99; flow rate: 0.6 ml min −1 Flow rate (ml min -1 ) to mass-transfer was minimized at lower flow rate, which was also discovered for protein-based CSPs. Table 2 summarizes the enantioseparation data obtained for four dansyl-amino acids on the newly synthesized NVC-CSP and a native ␤-cyclodextrin chiral stationary phase (250 mm×4.6 mm i.d., particle size, 5 m)synthesized according to Fujimura et al [21]. Our experiments gave better results, and furthermore, shorter separation times were needed for most of the solutes.…”

“…It is well known that the inclusion plays an important role in the interaction mechanism if native ␤-cyclodextrin CSP is used in reversed mode. According to the competitive inclusion model proposed by Fujimura et al [21], the side chain of dansyl-amino acids will compete with dansyl group to enter into the hydrophobic cavity. Probably due to the higher hydrophobicity and suitable size of it's side chain, Dns-But obtained no enantioseparation on the native ␤-cyclodextrin CSP, although it was more retained.…”

Capillary Zone Electrophoresis with Combined Use of γ-Cyclodextrin and a Metal Ion as a Novel Tool for Chiral Separation of Dansylamino Acids

“…In fact, similar results were also reported in the HPLC separation of DNS-D,L-amino acids on a y-CD column. 13 The relative standard deviations (n=5) of the migration times at pH 6.4 for DNS derivatives of D-Leu, L-Leu, D-Phe, L-Phe and D,L-Trp (not resolved) were 2.4, 2.8, 2.8, 2.7 and 2.6%, respectively; those for D-Leu, LLeu, D-Phe, L-Phe, D-Trp and L-Trp at pH 3.5 were 2.9, 2.8, 1.8, 2.0, 1.9 and 2.0%, respectively.…”

Enantiomeric Separations of Cationic and Neutral Compounds by Capillary Electrochromatography with β-Cyclodextrin-Bonded Charged Polyacrylamide Gels

“…AC-β-CD was synthesized according to a general method 11,12 with some modifications. The method was as follows: 1) a 5-g portion of β-CD was dried in vacuo at 60˚C for 8 h in the presence of di-phosphorous pentaoxide; 2) the dried β-CD was dissolved in 70 ml of dry pyridine; 3) 1 ml of allyl isocyanate was added dropwise to the β-CD pyridine solution with stirring; 4) the reaction solution was heated at 80˚C and kept standing for 6 h under a nitrogen atmosphere; 5) the reaction solution was cooled down to room temperature; 6) after pyridine was evaporated in vacuo, the raw product was purified by repeated recrystallization from acetone.…”