Gas‐chromatographic approach to probe the absence of molecular inclusion in enantioseparations by carbohydrates. Investigation of linear dextrins (“acyclodextrins”) as novel chiral stationary phases

Abstract

Acetylated/silylated maltooligosaccharides with different degrees of oligomerization have been tested as chiral stationary phases for enantioselective gas chromatography. The acyclic dextrin derivatives carrying tert-butyldimethylsilyl groups at the primary hydroxyl sites and acetyl groups at the secondary hydroxyl sites showed an unexpected ability for the enantioseparation of alpha-amino acid derivatives and halogenated compounds, in addition to some underivatized chiral compounds. Some examples of an improved enantioselectivity invoked by the linear CSPs as compared to that of cyclic oligosaccharides are demonstrated in this work. The results highlight the role of the polar external surface of the selector in lieu of the well-established inclusion mechanism of enantiorecognition by cyclic dextrins. Thus, the enantioseparation of chiral compounds on linear dextrin derivatives--devoid of a molecular cavity--sheds a new light on the mechanisms of enantiorecognition by cyclodextrin derivatives. In contrast to cyclodextrins, linear dextrins are readily accessible in both enantiomeric forms.

Separation of Enantiomers by Gas Chromatography on Chiral Stationary Phases

“…It was found that in selected cases the "acyclodextrins" showed even larger enantioseparation factors α than those shown by the cyclodextrins [107,108]. A change in the elution order has also been observed [108].…”

“…Even the parent building block glucose as the 2,3,4-tri-O-acetyl-1,6-di-O-tert-butyldimethylsilyl derivative was able to enantioseparate α-amino acids as N -TFA methyl esters [108]. One of the main advantages of the use of linear dextrin derivatives resides in the possibility of obtaining both d-and l-configurated (as well as epimeric) forms of the selectors, thereby widening the scope of enantioseparation, including tuning of the elution order of the enantiomers [108]. The results further underscore the difficulties in comprehending mechanisms of chirality recognition exhibited by dextrins.…”

Gas chromatographic enantioseparation of unfunctionalized chiral alkanes: A challenge in separation science (overview, state of the art, and perspectives)

“…The attempt to use linear dextrin selectors devoid of a real cavity is justified by previous successful enantioseparations in capillary electrophoresis by underivatized dextrins [39][40][41] and in GC by corn syrup, 42 amylose, 43,44 and cellulose 45 derivatives and recently by a multifunctional maltoheptaose derivative. 46,47 Although in some instances higher enantioseparations factors a were obtained with functionalized racemates, e.g. derivatized amino acids, on linear acetylated/silylated dextrins as compared to the corresponding cyclodextrin derivatives, 46,47 all tested chiral alkanes failed to be enantioseparated on permethylated maltoheptaose (G7) both in the dissolved or in the bonded form (Fig.…”

A Molecular docking study to predict enantioseparation of some chiral carboxylic acid derivatives by methyl-β-cyclodextrin

“…However, this assumption still contradictory because in some case, enantioseparation may occur at the outside of the cavity of the host molecule [54][55][56].…”