The usage of heptakis (2, 3, 6-tri-O-methyl)-beta-cyclodextrin as a gas chromatographic chiral stationary phase and as a discriminator in an enantioselective reaction

Abstract

Heptakis (2,3,6-tri-O-methyl)-beta-cyclodextrin (TRIMEB) was synthesized to use as a chiral gas chromatographic stationary phase and as a discriminator in reductive ring-opening of styrene oxide with sodium borohydride in water. TRIMEB was mixed with OV-1701 and was coated onto a capillary column by static method. By using this column, the analyte could be separated in the order of styrene oxide, 1-phenylethanol and 2-phenylethanol. For the chiral compounds, the S-enantiomers of both styrene oxide and 1-phenylethanol were eluted after the R-isomers. When TRIMEB was used as a chiral selector in reductive ring-opening of styrene oxide, no enantioselectivity on chiral product was observed and the main product was 2-phenylethanol similar to the reaction without chiral selector. Then the amount of TRIMEB was increased, similar results were still obtained and more styrene oxide was recovered. The other two types of cyclodextrin which possess hydroxyl groups (underivatized and randomly methylated) were also used in the same reaction. Both selectors provided 1-phenylethanol as the predominant, however, only underivatized cyclodextrin induced enantioselectivity in chiral product. Another interesting point discovered from the study was that the number of moles of cyclodextrin in the reaction plays more important role in product selectivity than the equivalent of selector.