Synthesis of a library of variously modified 4-methylumbelliferyl xylosides and a structure-activity study of human β4GalT7

Copper-promoted late-stage glycosylsulfonylation of aryl iodide and bromide to access glycosyl aryl sulfones

Glycosyl aryl sulfones exhibit diverse biological activities. Herein, we developed a copper-promoted coupling strategy using glycosyl sodium sulfinates and aryl iodides or bromides, enabling efficient synthesis of carbohydrate-based sulfone with broad functional group compatibility. This method offers a versatile approach for the late-stage modification of bioactive molecules.

Recent advances in the synthesis of Glycoconjugated heterocycles: A promising strategy for accessing bioactive compounds

Glycoconjugation of biologically relevant heterocycles and natural products to create glycohybrids, combining the unique features of both structures, has emerged as a promising approach for the creation of carbohydrate-based therapeutics. This review presents a comprehensive overview of the glyco-heterocycles synthesized primarily over the past decade, offering in-depth insights into the synthetic methods employed. Additionally, the review delves into the biological activities exhibited by these molecules, with particular emphasis on the structural elements that influence their therapeutic potential. It covers the molecular hybridization of biologically privileged heterocycles-including thiadiazole, oxadiazole, pyrazole, imidazole, thiazolidine, pyridine, pyrimidine, indole, benzimidazole, benzothiazole, coumarin, quinoline, etc. with carbohydrates and explores their biological activity. By integrating insights into both synthetic strategies and bioactivity, this work aims to enhance the understanding of glyco-heterocycles as a versatile class of compounds for medicinal chemistry and drug development.

Towards the synthesis of a 2-deoxy-2-fluoro-d-mannose building block and characterisation of an unusual 2-S-phenyl anomeric pyridinium triflate salt via 1 → 2 S-migration

Regio- and stereo-selective synthetic routes to 2-deoxy-2-fluoro-d-mannose building blocks are often experimentally challenging when using Selectfluor with the corresponding glycal. We targeted a late-stage method to introduce fluorine in a stereospecific manner using inversion via a triflate. Accordingly, synthesis of a conventionally protected 2-deoxy-2-fluoro-d-mannose β-thioglycoside donor, directly applicable to oligosaccharide synthesis, was attempted using C2-triflate inversion of the corresponding d-glucoside with TBAF. Unexpectedly, an anomeric pyridinium salt was isolated when attempting to form the C2-triflate using Tf2O in pyridine. Indicatively, this proceeds via a 1 → 2 S-migration delivering a 1,2-trans product with α-d-manno configuration and the anomeric pyridinium in a pseudo-equatorial position. The structure of this unexpected intermediate was confirmed in the solid-state using X-ray crystallography. Omission of the pyridine solvent led to dimer formation. Switching the aglycone to an O-para-methoxyphenyl enabled smooth C2 inversion to the desired 2-deoxy-2-fluoro d-mannose system, suitably equipped for further anomeric manipulation.

Chemical editing of proteoglycan architecture

Proteoglycans are heterogeneous macromolecular glycoconjugates that orchestrate many important cellular processes. While much attention has focused on the poly-sulfated glycosaminoglycan chains that decorate proteoglycans, other important elements of their architecture, such as core proteins and membrane localization, have garnered less emphasis. Hence, comprehensive structure-function relationships that consider the replete proteoglycan architecture as glycoconjugates are limited. Here we present an extensive approach to study proteoglycan structure and biology by fabricating defined semisynthetic modular proteoglycans that can be tailored for cell surface display. The expression of proteoglycan core proteins with unnatural amino acids permits bioorthogonal click chemistry with functionalized glycosaminoglycans for methodical dissection of the parameters required for optimal binding and function of various proteoglycan-binding proteins. We demonstrate that these sophisticated materials can recapitulate the functions of native proteoglycan ectodomains in mouse embryonic stem cell differentiation and cancer cell spreading while permitting the analysis of the contributing architectural elements toward function.

Deoxy sugars. General methods for carbohydrate deoxygenation and glycosidation

Deoxy sugars represent an important class of carbohydrates, present in a large number of biomolecules involved in multiple biological processes. In various antibiotics, antimicrobials, and therapeutic agents the presence of deoxygenated units has been recognized as responsible for biological roles, such as adhesion or great affinity to receptors, or improved efficacy. The characterization of glycosidases and glycosyltranferases requires substrates, inhibitors and analogous compounds. Deoxygenated sugars are useful for carrying out specific studies for these enzymes. Deoxy sugars, analogs of natural substrates, may behave as substrates or inhibitors, or may not interact with the enzyme. They are also important for glycodiversification studies of bioactive natural products and glycobiological processes, which could contribute to discovering new therapeutic agents with greater efficacy by modification or replacement of sugar units. Deoxygenation of carbohydrates is, thus, of great interest and numerous efforts have been dedicated to the development of methods for the reduction of sugar hydroxyl groups. Given that carbohydrates are the most important renewable chemicals and are more oxidized than fossil raw materials, it is also important to have methods to selectively remove oxygen from certain atoms of these renewable raw materials. The different methods for removal of OH groups of carbohydrates and representative or recent applications of them are presented in this chapter. Glycosidic bonds in general, and 2-deoxy glycosidic linkages, are included. It is not the scope of this survey to cover all reports for each specific technique.

Fluorescently labeled xylosides offer insight into the biosynthetic pathways of glycosaminoglycans

Five novel xylosides tagged with the fluorescent probe Pacific Blue™ were synthesized and found to act as substrates for β4GalT7, a bottleneck enzyme in the biosynthetic pathways leading to glycosaminoglycans. By confocal microscopy of A549 cells, we showed that the xylosides were taken up by the cells, but did not enter the Golgi apparatus where most of the glycosaminoglycan biosynthesis occurs. Instead, after a possible double galactosylation by β4GalT7 and β3GalT6, the biosynthesis was terminated. We hypothesize this is due to the charge of the fluorescent probe, which is required for fluorescent ability and stability under physiological conditions.

Fluorescently labeled xylosides are taken up by cells and initiate priming of labeled GAG chains of various length.

Synthesis of oligosaccharides of the linkage region of proteoglycans using regioselective glycosylation

Proteoglycans (PGs) are complex macromolecules that are composed of glycosaminoglycan (GAG) chains covalently attached to a core protein through a tetrasaccharide linker. Biosynthesis of PGs is complex and involves a large number of glycosyltranferases. We report herein for the first time the synthesis of a collection of various sulfoforms of the disaccharide GlcA-1,3-β-d-Gal and trisaccharides GlcNAc-1,4-α-d-GlcA-1,3-β-d-Gal and GalNAc-1,4-β-d-GlcA-1,3-β-d-Gal using a regioselective glycosylation. Preliminary results on the impact of sulfation of these disaccharides upon recombinant chondroitin sulfate N-acetylgalactosaminyltransferase-1 (CSGalNAcT-1) involved in chondroitin sulfate chain initiation is also reported.