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

A novel norvancomycin-bonded chiral stationary phase (NVC-CSP) was synthesized by using the chiral selector of norvancomycin. The chiral separation of enantiomers of several dansyl-amino acids by high-performance liquid chromatography (HPLC) in the reversed-phase mode is described. The effects of some parameters, such as organic modifier concentration, column temperature, pH and flow rate of the mobile phase, on the retention and enantioselectivity were investigated. The study showed that ionic, as well as hydrophobic interactions were engaged between the analyte and macrocycle in this chromatographic system. Increasing pH of buffers usually improved the chiral resolution for dansyl-alpha-amino-n-butyric acid (Dns-But), dansyl-methionine (Dns-Met) and dansyl-threonine (Dns-Thr), but not for dansyl-glutamic acid (Dns-Glu) which contains two carboxylic groups in its molecular structure. The natural logarithms of selectivity factors (lnalpha) of all the investigated compounds depended linearly on the reciprocal of temperature (1/T), most processes of enantioseparation were controlled enthalpically. Interestingly, the process of enantioseparaton for dansyl-threonine was enthalpy-controlled at pH of 3.5, while at pH of 7.0, it was entropy-controlled according to thermodynamic parameters Delta(R,S)DeltaH degrees and Delta(R,S)DeltaS degrees afforded by Van't Hoff plots. In order to get baseline separation for all the solutes researched, norvancomycin was also used as a chiral mobile phase additive. In combination with the NVC-CSP, remarkable increases in enanselectivity were observed for all the compounds, as the result of a "synergistic" effect.

[Simple preparation and evaluations of amide-octyl-bonded phase].

A simple preparation process of amide-octyl-bonded phase (AOBP) is described. In the process aminopropyltriethoxysilane first reacted with octanoyl chloride and then the obtained intermediate was bonded onto porous silica. Characterization of prepared packing was carried out with elemental analysis, solid-state nuclear magnetic resonance (13C-NMR) and Fourier transform infrared (FTIR) spectroscopy. Chromatographic evaluations were carried out by testing with a mixture including acidic, basic and neutral organic compounds using methanol-water as binary mobile phase. The results show that the stationary phase has excellent chromatographic properties and resistance to hydrolysis between pH 2.5-7.5. It can be used for the efficient separation of basic compounds.