Evaluation of norbornene- beta-cyclodextrin-based monomers and oligomers as chiral selectors by means of nonaqueous capillary electrophoresis.
Norbornen-5-yl carboxylic acid and norbornen-5-ylmethylsilyl ether-based beta-cyclodextrins (beta-CDs) containing up to three norbornene ester and up to five norbornene silyl ether units have been prepared from beta-CD and norbornen-5-carboxylic chloride and norbornen-5-ylmethyldichlorosilane, respectively. Oligomers (n = 2-4) were prepared therefrom using ring-opening metathesis polymerization (ROMP). Monomeric and oligomeric substituted beta-CDs were evaluated as chiral selectors in nonaqueous capillary zone electrophoresis using 35 mM sodium bicarbonate in N-methylformamide (NMF) as background electrolyte. Both monomeric and oligomeric norbornene ester- and norbornene silyl ether-type selectors showed good enantioresolution for dansylated (DNS-) amino acids using concentrations of the chiral selector of up to 4% w/v. A significant improvement in resolution was observed upon the introduction of up to five norbornene silyl ether units into a beta-CD molecule, whereas higher degrees of substitution with norbornen-5-yl-carboxyl groups lead to a reduction in enantioresolution of DNS-amino acids. Thus, pentakis(norbornen-5-ylmethylhydroxysiloxyl)-beta-CD turned out to be superior to mono(norbornen-5-ylmethylhydroxysiloxyl)-beta-CD in terms of enantioresolution. Moreover, norbornene silyl ether-type selectors were found to be more efficient than norbornene ester-type selectors. Finally, oligomeric selectors were found to possess superior or at least comparable enantioselectivity in the separation of DNS-amino acids compared to the parent monomers. A maximum in enantioresolution was obtained with oligo(pentakis(norbornen-5-ylmethylhydroxysiloxyl)beta-CD).
Eder
K
K
Institute of Analytical Chemistry and Radiochemistry, Leopold-Franzens-University, Innsbruck, Austria.
Sinner
F
F
Mupa
M
M
Huber
C G
CG
Buchmeiser
M R
MR
D002240:Carbohydrate Sequence; D003505:Cyclodextrins / Q000032:analysis*; D019075:Electrophoresis, Capillary / Q000379:methods*; D004987:Ethers; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009636:Norbornanes / Q000032:analysis*; D047392:beta-Cyclodextrins
D003505:Cyclodextrins; D004987:Ethers; D009636:Norbornanes; D047392:beta-Cyclodextrins; C046060:2-norbornene; C031215:betadex