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

Three pi-acid type chiral stationary phases based on monochloro-substituted phenyl carbamates of beta-cyclodextrin have been synthesized. First, beta-cycloclextrin was reacted with 5-bromo-1-pentene in dry DMF at room temperature to give 6(A)-O-(4'-pentenyl)-beta-cyclodextrin. The remaining twenty hydroxyl groups of this derivatized beta-cyclodextrin were blocked by further reaction with 2-chlorophenyl isocyanate, 3-chlorophenyl isocyanate, and 4-chlorophenyl isocyanate in dry pyridine, at 85 degreesC, to yield the three corresponding carbamates. After hydrosilylation with triethoxysilane at 80 degreesC, catalysed by tetra(triphenylphosphine)platinum (0), these carbamates were anchored on to silica gel by heating under reflux in toluene. All the beta-cyclodextrin derivatives and CSPs prepared were characterized by IR and H-1 NMR spectroscopy and elemental analysis. The surface concentrations of 2-chlorophenyl carbamoylated beta-cyclodextrin, 3-chlorophenyl carbamoylated beta-cyclodextrin, and 4-chlorophenyl carbamoylated beta-cyclodextrin on silica gel were 0.27, 0.28 and 0.30 mumol 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.