Monochloro-substituted phenyl carbamoylated β-cyclodextrins as π-acid chiral stationary phases for high-performance liquid chromatography

Abstract

Three π-acid type chiral stationary phases based on monochloro-substituted phenyl carbamates of β-cyclodextrin have been synthesized. First, β-cyclodextrin was reacted with 5-bromo-1-pentene in dry DMF at room temperature to give 6A-O-(4′-pentenyl)-β-cyclodextrin. The remaining twenty hydroxyl groups of this derivatized β-cyclodextrin were blocked by further reaction with 2-chlorophenyl isocyanate, 3-chlorophenyl isocyanate, and 4-chlorophenyl isocyanate in dry pyridine, at 85°C, to yield the three corresponding carbamates. After hydrosilylation with triethoxysilane at 80°C, catalysed by tetra(triphenylphosphine)platinum(0), these carbamates were anchored on to silica gel by heating under reflux in toluene. All the β-cyclodextrin derivatives and CSPs prepared were characterized by IR and 1H NMR spectroscopy and elemental analysis. The surface concentrations of 2-chlorophenyl carbamoylated β-cyclodextrin, 3-chlorophenyl carbamoylated β-cyclodextrin, and 4-chlorophenyl carbamoylated β-cyclodextrin on silica gel were 0.27, 0.28 ond 0.30 μmol m-2, respectively. Under normal-phase conditions the separation ability of CSPs containing 3- and 4-chlorophenyl carbamate was better than that of the CSPs containing 2-chlorophenyl carbamate.