Heptakis[2,3‐di‐O‐methyl‐6‐O‐(L‐valine‐tert‐butylamide‐N^α‐ylcarbonylmethyl)]‐β‐cyclodextrin: a New Multifunctional Cyclodextrin CSA for the NMR Enantiodiscrimination of Polar and Apolar Substrates

Abstract

Heptakis[2,3‐di‐O‐methyl‐6‐O‐(L‐valine‐tert‐butylamide‐Nα‐ylcarbonylmethyl)]‐β‐cyclodextrin with methyl groups on the secondary sites and a diamide chiral selector on the primary ones showed considerable utility as a CSA in the NMR enantiodiscrimination of a wide spectrum of amino acid derivatives, while also allowing trisubstituted allenes to be enantiodiscriminated. Enantiodiscrimination processes were investigated by Diffusion‐Ordered SpectroscopY (DOSY). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Separation of Enantiomers by Gas Chromatography on Chiral Stationary Phases

“…The selector Valdex (heptakis[6-O-(N -acetylyl-l-valine-tertbutylamide)-2,3-O-methyl]-β-cyclodextrin) represents a versatile chiral solvating agent (CSA) for the NMR spectroscopic discrimination of enantiomers which associate either with the permethylated cyclodextrin selector (e.g., for apolar trisubstituted allenes) or with the diamide selector (e.g., for polar 2-alkyl-α-amino acid derivatives) [164], but no remarkable enantioseparations of different classes of compounds were observed on Chirasil-Valdex in the GC mode. However, promising results have been obtained on a selector that carries only a single l-valine diamide moiety in the C6-position of permethylated β-cyclodextrin for enantioseparations by GC [165].…”

External vs. Internal Interactions in the Enantiodiscrimination of Fluorinated α‐Amino Acid Derivatives by Heptakis[2,3‐di‐O‐acetyl‐6‐O‐(tert‐butyldimethylsilyl)]‐β‐cyclodextrin, a Powerful Chiral Solvating Agent for NMR Spectroscopy

“…[18][19][20] The potential of selective placing of different functional groups on the wide and narrow cyclodextrin rims was also exploited, and this approach led to CSAs with enhanced enantiodiscriminating properties. [20][21][22] Among derivatized cyclodextrins, heptakis[2,3-di-O-acetyl-6-O-(tert-butyldimethylsilyl)]-β-cyclodextrin (1, Scheme 1) has already become established as a powerful chiral stationary phase (CSP) for the gas-chromatographic separation [23] of stereoisomeric flavour compounds. The development of analogously modified linear dextrins ("acyclodextrins") for use in enantioselective gas chromatography (GC) provided additional insights regarding the role of cavity and the number of derivatized glucose units in the enantiodiscrimination processes.…”