Synthesis, NMR spectroscopic characterization and polysiloxane-based immobilization of the three regioisomeric monooctenylpermethyl-β-cyclodextrins and their application in enantioselective GC

2(I-VI), 3(I-VII), 6(I-VII)-Eicosa-O-methyl-2(I)-O-(oct- 7 -enyl)cyclomaltoheptaose, 2(I)-(VII),3(I-VI),6(I-VII)-eicosa-O-methyl-3(I)-O-(oct-7-enyl)cyclomaltoheptaose, and 2(I-VII),3(I-VII),6(I-VI)-eicosa-O-methyl-6(I)-O-(oct-7-enyl)cyclomaltoheptaose were synthesized by selective introduction of an oct-7-enyl group at one of the O-2, O-3, or O-6 positions of selectively methylated cyclomaltoheptaose (beta-cyclodextrin, CD) and, depending on the synthetic route, by a subsequent permethylation step. Each of the regioisomeric mono-oct-7-enylated permethylated beta-cyclodextrin derivatives was anchored by hydrosilylation to a hydridomethyldimethylsiloxane copolymer to yield unambiguously O-2-, O-3-, and O-6-bonded chiral stationary phases (CSP) of Chirasil-Dex, which were evaluated in enantioselective gas chromatography (GC). O-6-Chirasil-Dex displayed slightly inferior enantioselectivity relative to either O-3- or O-2-Chirasil-Dex. The statistical synthesis of the CSP by mono-oct-7-enylation of beta-CD under varying reactions conditions (base, solvent), without the use of hydroxy group protection chemistry, furnished a mixture of O-6- and O-2-Chirasil-Dex in dimethylformamide and predominantly the O-2-regioisomer in dimethyl sulfoxide. Chirasil-Dex, previously formulated exclusively as the O-6 regioisomer, should be revised as an O-2- and O-6-Chirasil-Dex mixture. (C) Wiley-VCH Verlag GmbH Co.