Journal
CHIRALITY
Volume 22, Issue 3, Pages 336-346Publisher
WILEY
DOI: 10.1002/chir.20748
Keywords
enantiomeric discrimination; H-1 NMR spectroscopy; carboxymethylated cyclodextrins; cyclodextrins; enantiomeric purity; lanthanide shift reagent
Funding
- National Science Foundation Research at Undergraduate Institutions Program [CHE-0244742, CHE-0653711, CHE-0115579]
- Howard Hughes Medical Institute
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Cyclodextrins that are indiscriminately carboxymethylated at the 2-, 3-, and 6-positions are used as chiral NMR solvating agents for cationic substrates with phenyl, naphthyl, pyridyl, indoline, and indole rings. Enantiodifferentiation with the alpha-, beta-, and gamma-cyclodextrin derivatives is compared. The carboxymethylated derivatives are almost always more effective as chiral NMR solvating agents for cationic substrates than native cyclodextrins. The most effective carboxymethylated cyclodextrin varies for different substrates, and at times even different resonances of the substrate. Addition of paramagnetic praseodymium(III) or ytterbium(III) to mixtures of the carboxymethylated cyclodextrin and substrate often causes enhancements in enantiomeric discrimination and facilitates measurements of enantiomeric purity. The lanthanide ion bonds to the carboxymethyl groups and causes perturbations in the chemical shifts in the NMR spectra of substrate molecules in the cyclodextrin cavity. Chirality 22:336-346, 2010. (C) 2009 Wiley-Liss, Inc.
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