New and old NMR experiments for the resonance assignment of complex oligosaccharides--application to a cyclodextrin derivative.

The complete assignment of the (1)H and (13)C sugar resonances in mono-3,6-anhydro-heptakis(2,3-O-methyl)-hexakis(6-O-methyl)-ß-cyclodextrin, an asymmetrically functionalized ß-cyclodextrin, was carried out by means of 2D NMR experiments. The TOCSY and the homonuclear multiple relay COSY spectra provided most of the (1)H assignments. The multiplicity edited HSQC and a set of F(1) selective HSQC-TOCSY and multiple relay HSQC-COSY spectra gave access to most of the (13)C chemical shifts. The latter were fully and accurately determined by means of a pair of complementary, highly folded HSQC-TOCSY spectra. The TOCSY-ROESY and ROESY-TOCSY spectra yielded the sequential assignment of the sugar units. A high resolution F(1) selective F(1) decoupled version of the TOCSY-ROESY experiment was recorded.

An alternative scheme for the multiplexed acquisition of 1D and 2D NMR spectra.

Spin system selective 1D (1)H, 2D DQF-COSY and 2D HSQC NMR spectra were recorded in order to fully assign the (1)H and (13)C 1D NMR spectra of an asymmetrical beta-cyclodextrin derivative. Instead of individually accessing the seven sugar anomeric protons by means of long multiplet selective pulses, only short region selective pulses were used. The simultaneously selected anomeric protons were differentiated by allowing their magnetization to evolve under the sole effect of the chemical shift interaction. In each experiment, the seven recorded spectra were linear combinations of the seven desired ones. The combination coefficients were measured and used to obtain almost perfectly separated sugar unit sub-spectra. This multiplexed acquisition scheme resulted in a time gain factor of about 2.

(L)- or (D)-valine tert-butylamide grafted on permethylated beta-cyclodextrin derivatives as new mixed binary chiral selectors: versatile tools for capillary gas chromatographic enantioseparation.

This work deals with the synthesis of two mixed binary chiral selectors prepared by grafting (L)- or (D)-valine tert-butylamide on permethylated cyclodextrin macrocycle. The enantioselective properties of the new chiral selectors diluted in OV11 polysiloxane (35% phenyl- and 65% methylsiloxane) were investigated by means of injections of 117 racemic mixtures. The mixed chiral selectors with (L)-valine and, to a lesser extent with (D)-valine, were found to have an improved enantioselectivity toward amino acid derivatives by comparison to permethylated cyclodextrin. The enantioseparation capability of these new chiral selectors has proven to be slightly less efficient than Chirasil-L-Val (Alltech) for amino acid derivatives, but it has been extended to include terpenes, lactones, esters, aliphatic compounds and aryl alcohols.