The double‐DANTE sequence applied to NMR of complex carbohydrates

Abstract

The double-DANTE sequence was implemented in 1D TOCSY and NOESY experiments to overcome some typical problems in the NMR of carbohydrates. In the 1D TOCSY experiment the double-DANTE sequence serves to invert simultaneously two resonances belonging to the same scalar-coupled spin system, thereby substantially increasing the sensitivity of the technique for subspectral editing and providing a valuable alternative to relayed TOCSY in overcoming small-1 bottlenecks in monosaccharides such as galactose and sialic acid. Spindiffusion artifacts in ID NOESY experiments that are mediated by more than one spin can be effectively eliminated by applying a double-DANTE pulse train for saturation of the mediators during the mixing time. In certain cases, the double-DANTE sequence is also capable of eliminating the three-spin effect in ID 13C{1H} NOE difference spectroscopy. KEY WORDS Double-DANTE 1 D TOCSY 1D NOESY Heteronuclear NOE CarbohydratesThe ring proton region of the 'H NMR spectrum of a carbohydrate is notoriously crowded; typically, for an oligosaccharide consisting of three or more monosaccharide residues, over 80% of the resonances in the spectrum overlap, in part or completely, between 6 3.3 and 3.9 ppm. The spectral complexity severely hampers the analysis of homo-and hetero-nuclear scalar and dipolar connectivities for carbohydrates. However, a few signals, including those of the anomeric (H-1) protons and of protons at deoxy carbons, are individually recognizable; they are commonly referred to as 'structural reporter groups." Those resonances are sufficiently separated from each other to allow for selective irradiation, making selective one-dimensional (1D) NMR experiments for carbohydrates often more attractive than their 2D analogues.The most powerful technique for spectral analysis of carbohydrates is homonuclear Hartmann-Hahn spectroscopy, called HOHAHA' or TOCSY.3 In a 1D TOCSY experiment, magnetization is transferred by isotropic mixing, for example from proton H-1 to other spins within the scalar coupled network (i.e. monosaccharide residue), through consecutive 3J(HH') and 2J(HH') coupling^.^ The sensitivity of the method, however, is limited by the magnitudes of the coupling constants. For example, the assignment of ring proton resonances for galactose (Gal) or N-acetylgalactosamine (GalNAc) residues by I D TOCSY on selective inversion of H-1 is only straightforward up to proton H-4 because of the small value for 35(45) (<1.5 Hz); similarly, magnetization originating from inversion of one of the H-3 protons in a sialic acid (NeuAc) residue readily

The solution conformation of sialyl-α(2→6)-lactose studied by modern NMR techniques and Monte Carlo simulations

“…The heteronuclear 1D NOE difference spectra were obtained with selective presaturation of IH resonances using the DANTE-z pulse sequence (Boudot et al, 1989) for saturation of one resonance at a time, or applying two interleaved DANTE pulse trains (Geen et al, 1989;Poppe and Van Halbeek, 1991b) for simultaneous irradiation of 2 resonances. One of the trains consisted of short pulses with rotating phase (in 60 ~ steps for the simultaneous irradiation of NeuAc H3ax and H3eq, and in 30 ~ steps for the Gal H6R and H6S protons); the second train consisted of the same short pulses with phase inversion of the even-numbered pulses every 8 scans together with the receiver phase, in analogy to the DANTE-z scheme (Poppe and Van Halbeek, 1991b).…”

“…Their values, in combination with the aforementioned NOE effects, can now be utilized more readily for determination of the conformation of glycosidic bonds. Finally, heteronuclear NOE contacts may be useful in situations where one of the above methods fails, for example when the anomeric carbon'is a quaternary carbon atom (Poppe and Van Halbeek, 1991b).…”

Excitation-Sculptured Indirect-Detection Experiment (EXSIDE) for Long-Range CH Coupling-Constant Measurement

“…Modifications of HSQC experiments to generate pure absorption-mode spectra in both F 1 and F 2 dimen-pulses (35). An increase in the length of the echo delays (D 1 and/or D 2 ) affects only the amplitude of the magnetizasions and measure the heteronuclear couplings along the proton dimension have also been proposed (24,26). The tion (due to increased loss through relaxation), as long as only resonances that are not coupled to each other are seinterference of in-phase homonuclear couplings with the antiphase heteronuclear couplings still exists as long as one lected (which can be typically achieved by examining a COSY spectrum).…”

The use of the AMBER force field in conformational analysis of carbohydrate molecules: Determination of the solution conformation of methyl α‐lactoside by NMR spectroscopy, assisted by molecular mechanics and dynamics calculations

“…34 The selective 90" proton pulse was of 15 ms, and that of 13C was of 2 ms. These pulses were achieved through gaussian-shaped DANTE sequences, using a programmable pulse modulator for the proton channel.…”