Chemical Synthesis of Residue-Selectively 13C and 2H Double-Isotope-Labeled Oligosaccharides as Chemical Probes for the NMR-Based Conformational Analysis of Oligosaccharides

Context Effects on Human Milk Oligosaccharide Linkage Conformation and Dynamics Revealed by MA'AT Analysis

An emerging NMR method, MA'AT analysis, has been applied to investigate context effects on the conformational properties of several human milk oligosaccharides (HMOs). The MA'AT model of the β-(1→4) linkage in the disaccharide, methyl β-lactoside (MeL), was compared to those obtained for the same linkage in the HMO trisaccharides, methyl 2'-fucosyllactoside (Me2'FL) and methyl 3-fucosyllactoside (Me3FL), and in the tetrasaccharide, methyl 2',3-difucosyllactoside (Me2',3DFL). MA'AT analysis revealed significant context effects on the mean values and circular standard deviations (CSDs) of the psi (ψ) torsion angles in these linkages. α-Fucosylation at both O2'Gal and O3Glc of MeL to give Me2',3DFL significantly constrained librational motion about ψ (70% reduction in the CSD) and shifted its mean value by ∼18°. α-Fucosylation at the O3Glc of MeL to give Me3FL constrained ψ more than α-fucosylation at the O2Gal to give Me2'FL. These effects can be explained by the expected solution conformation of Me3FL, which closely resembles the Lewisx trisaccharide. Comparisons of MA'AT models of ψ to those obtained by 1 μs aqueous molecular dynamics simulation (GLYCAM06) revealed identical trends, that is, MA'AT analysis was able to recapitulate molecular behavior in solution that was heretofore only available from MD simulation. The results highlight the capabilities of MA'AT analysis to determine probability distributions of molecular torsion angles in solution as well as degrees of librational averaging of these angles.

Unlocking the mysteries of milk oligosaccharides: Structure, metabolism, and function

Milk oligosaccharides (MOs), complex carbohydrates prevalent in human breast milk, play a vital role in infant nutrition. Serving as prebiotics, they inhibit pathogen adherence, modulate the immune system, and support newborn brain development. Notably, MOs demonstrate significant variations in concentration and composition, both across different species and within the same species. These characteristics of MOs lead to several compelling questions: (i) What distinct beneficial functions do MOs offer and how do the functions vary along with their structural differences? (ii) In what ways do MOs in human milk differ from those in other mammals, and what factors drive these unique profiles? (iii) What are the emerging applications of MOs, particularly in the context of their incorporation into infant formula? This review delves into the structural characteristics, quantification methods, and species-specific concentration differences of MOs. It highlights the critical role of human MOs in infant growth and their potential applications, providing substantial evidence to enhance infant health and development.

[13 C+D] Double Labeling with Calcium Carbide: Incorporation of Two Labels in One Step

D-labeling is a valuable tool in advanced synthetic chemistry and pharmacy. However, D-incorporation significantly complicates the identification of products. In fact, D labels are invisible in ¹ H-NMR spectra and cause undesirable splitting in ¹³ C-NMR spectra which decreases the detectable limits. At the same time, ² H-NMR spectra are not effective for precise identification due to low sensitivity and the absence of correlations with ¹ H atoms. Here, ¹³ C-label was considered as an accompanying label for D-label in [¹³ C+D] unit for identification of D-containing sites and to track D-labels. [¹³ C+D]-doubly labeled vinyl derivatives and triazoles were synthesized using ¹³ C-labeled calcium carbide as a source of ¹³ C-label and deuterium oxide as a source of D-label. The reaction occurred in one-step manner accompanied with in situ doubly labeled acetylene formation. Non-labeled, mono-labeled and doubly labeled substrates were isolated in 25-80% yields.

Atom-economical synthesis of 1,2-bis(phosphine oxide)ethanes from calcium carbide with straightforward access to deuterium- and 13C-labeled bidentate phosphorus ligands and metal complexes

Straightforward access to bidentate phosphorus ligands and bis(phosphineoxide)ethanes is described based on atom-economic addition reaction. A practical approach was developed to incorporate 2H and 13C labels using easily available reagents.

Structural Analysis of Oligosaccharides and Glycoconjugates Using NMR

Carbohydrate chains play critical roles in cellular recognition and subsequent signal transduction in the nervous system. Furthermore, gangliosides are targets for various amyloidogenic proteins associated with neurodegenerative disorders. To better understand the molecular mechanisms underlying these biological phenomena, atomic views are essential to delineate dynamic biomolecular interactions. Nuclear magnetic resonance (NMR) spectroscopy provides powerful tools for studying structures, dynamics, and interactions of biomolecules at the atomic level. This chapter describes the basics of solution NMR techniques and their applications to the analysis of 3D structures and interactions of glycoconjugates in the nervous system.

Synthetic Approaches to Break the Chemical Shift Degeneracy of Glycans

NMR spectroscopy is the leading technique for determining glycans' three-dimensional structure and dynamic in solution as well as a fundamental tool to study protein-glycan interactions. To overcome the severe chemical shift degeneracy of these compounds, synthetic probes carrying NMR-active nuclei (e. g., 13 C or 19 F) or lanthanide tags have been proposed. These elegant strategies permitted to simplify the complex NMR analysis of unlabeled analogues, shining light on glycans' conformational aspects and interaction with proteins. Here, we highlight some key achievements in the synthesis of specifically labeled glycan probes and their contribution towards the fundamental understanding of glycans.