Sequential analysis of oligosaccharide structures by modern NMR techniques

Abstract

Sequential analysis of oligosaccharide structures can b e transfer and NOE have been used to determine the sequence achieved by semiselective NMR-pulse techniques. Gaussianshaped pulses combined with multistep-relayed coherence and assign the carbohydrate resonances of lanatoside C.The structure elucidation of oligosaccharides on the basis of NMR analytical data is an extremely difficult task because it requires the determination of monosaccharide units, their anomeric configuration, their sequence and the position of the glycosidation. Recently, the potential of modern 2D-NMR techniques, in sequencing oligosaccharides, has been demonstrated 1-3). Information about the primary structure is usually obtained by the determination of interresidue NOE 4-6) or long-range scalar coupling across the glycosidic bonds 2, combined with glycosylation-induced shifts. The main disadvantage of these methods is their low sensitivity and heavy signal overlap even at very high fields. This can be particulary misleading when NOES, correlated with an anomeric proton, appear at a chemical shift shared by two or more different hydrogens.We describe I D versions of 2D experiments which can be used to determine the structure of the monosaccharide residues and their sequence. They are much more sensitive than their 2D counterparts and can be performed with much higher digital resolution. Because of the selective nature of these methods only the desired signals of heavy overlapping resonances can be observed.I D versions of 2D-NMR experiments" are obtained by using Gaussian-shaped pulses') for selective COSY experiments, combined with one-or two-step-relayed coherence transfer 9! They have been used to analyse carbohydrate spectra") and to determine the structure of a bisdesmosidic saponin containing ten sugar residues"). We show that semiselective excitation of one carbohydrate proton, combined with multistep-relayed coherence transfer and a terminal NOE transfer, can be used for the determination of the sequence of complex oligosaccharides. unit combined with up to three-step-relayed coherence transfer allows all glucose resonances to be assigned.

Complete1H and13C assignments of theDigitalis lanata cardenolides, glucodigifucoside and glucogitoroside by 1D and 2D NMR

“…3) and some interproton coupling constants were calculated from careful inspection of the 1D spectrum. The 1H chemical shifts of the digitoxose ring obtained in this work were also fairly close to those reported for this sugar residue in digoxin,8 digitoxin9 and lanatoside C. 10 In summary, the present work provides, for the Ðrst time, the complete 1H and 13C assignments for Ggr and also conÐrms the earlier partial assignments for Gdf.…”

Nuclear Magnetic Resonance Spectroscopic Approaches for the Determination of Interglycosidic Linkage and Sequence in Oligosaccharides

“…The total acquisition time needed to perform one or more 2D experiments is in practice, often prohibitive and this has led to the development of experiments combining different polarization transfer mechanisms in a 1D manner, where only one spin is selectivity excited at the beginning of the pulse sequence. The I D COSY in conjunction with multistep RCT or 1D TOCSY can be used to assign all resonances of a particular carbohydrate residue which in combination with NOE transfer, gives the NOE at the resonance of the following carbohydrate residue (Haslinger et al, 1990). The 1D NOESY or 1D ROESY difference experiments, in an analogous manner, yield information about the IGL (Haslinger et al, 1990;Wessel et al, 1991).…”

“…The I D COSY in conjunction with multistep RCT or 1D TOCSY can be used to assign all resonances of a particular carbohydrate residue which in combination with NOE transfer, gives the NOE at the resonance of the following carbohydrate residue (Haslinger et al, 1990). The 1D NOESY or 1D ROESY difference experiments, in an analogous manner, yield information about the IGL (Haslinger et al, 1990;Wessel et al, 1991). The applicability of the 1D COSY technique for the detection of long-range coupling indicative of sequence has also been suggested (Uhrin et al, 1994b;Uhrinova et al, 1991).…”

Profiling and structural analysis of cardenolides in two species of Digitalis using liquid chromatography coupled with high-resolution mass spectrometry

“…The rest of the cardenolides detected belonged to the level 2b or 3, putatively characterized compounds as the spectra of these compounds are not found in the available spectral libraries such as Metlin and Global Natural Product Social Molecular Networking (GNPS) [26,27]. Nevertheless, the cardenolides observed were more than likely to be correctly annotated because 1, they were all identified in the respective species of Digitalis previously and were validated by methods including NMR [ [7,22,[28][29][30][31][32]; 2, HRMS enabled definite determination of formula for both precursor and product ions; 3, no purpurea glycosides were identified in D. lanata and no lanatosides were detected in D. purpurea, validating the specificity of the method; 4. the elution sequence of cardenolides on a C18 column highly resembled preceding reports [7]. For D. lanata, 17 out of 59 cardenolides previously identified by HPLC were confirmed and structurally annotated in our method.…”