Synthesis of Homo- and Heteromultivalent Fucosylated and Sialylated Oligosaccharide Conjugates via Preactivated N-Methyloxyamine Precision Macromolecules and Their Binding to Polyomavirus Capsid Proteins

Glycoconjugates are a versatile class of bioactive molecules that have found application as vaccines and antivirals and in cancer therapy. Their synthesis typically involves elaborate functionalization and use of protecting groups on the carbohydrate component in order to ensure efficient and selective conjugation. Alternatively, non-functionalized, non-protected carbohydrates isolated from biological sources or derived through biotechnological methods can be directly conjugated via N-methyloxyamine groups. In this study, we introduce such N-methyloxyamine groups into a variety of multivalent scaffolds─from small to oligomeric to polymeric scaffolds─making use of solid-phase polymer synthesis to assemble monodisperse sequence-defined macromolecules. These scaffolds are then successfully functionalized with different types of human milk oligosaccharides deriving a library of homo- and heteromultivalent glycoconjugates. Glycomacromolecules presenting oligosaccharide side chains with either α2,3- or α2,6-linked terminal sialic acid are used in a binding study with two types of polyomavirus capsid proteins showing that the multivalent presentation through the N-methyloxyamine-derived scaffolds increases the number of contacts with the protein. Overall, a straightforward route to derive glycoconjugates from complex oligosaccharides with high variability yet control in the multivalent scaffold is presented, and applicability of the derived structures is demonstrated.

Lactosyl-sepharose binding proteins from pancreatic cancer cells show differential expression in primary and metastatic organs

In normal cells, glycan binding proteins mediate various cellular processes upon recognition and binding to respective ligands. In tumor cells, these proteins have been associated with metastasis. Lactosyl-sepharose binding proteins (LSBPs) were isolated and identified in a workflow involving lactosyl affinity chromatography and label-free quantification mass spectrometry (LFQ MS). A binding study with monosaccharides was performed by microscale thermophoresis and nuclear magnetic resonance spectroscopy. Influence of galactose on LSBPs’ binding to the lactosyl resin was investigated by competitive affinity chromatography followed by LFQ MS. An analysis of amino acids with sugar binding motifs was searched using bioinformatics tools. The expression profiles of these proteins at the mRNA level, as determined by a chip array from a pancreatic ductal adenocarcinoma (PDAC) liver metastasis model, were used for evaluating their potential role in cancer progression. Proteomics data and their respective genes were analyzed by MaxQuant and Ingenuity Pathway Analysis. In total, 1295 LSBPs were isolated and identified from Suit2-007 human pancreatic adenocarcinoma cells. Interaction studies revealed that these proteins exhibit low to moderate affinity for monosaccharide sugars. Some of these LSBPs even showed reduced affinity after calcium depletion. Among the isolated proteins were annexins and galectins in addition to other families, with no history of binding lactosyl residues. A subset of LSBPs exhibited differential profiles in the pancreas, liver, and lung environments. These modulations may be related to tumor progression. In conclusion, we show that PDAC cells contain LSBPs, a subset of which binds galactose with calcium dependency. The differential expression of these proteins in a rat model highlights their value for diagnosis and as potential drug targets for PDAC therapy. Future work will be required to validate these findings in patient samples.

Impact statement

Interaction of glycan binding proteins with aberrantly expressed glycans in tumor environment is crucial for metastasis. Here, we established a work flow for investigating the presence of a subset of these proteins in PDAC cells, which bind to a lactosyl-sepharose resin. The resin had been designed to isolate proteins with lectin-like properties. The corresponding lactosyl-sepharose binding proteins (LSBPs) show affinity for galactose and other monosaccharides. A subset of the LSBPs shows also calcium dependency. The importance of these proteins is highlighted by their differential expression profiles in PDAC cells growing in primary (pancreas) and metastatic (liver and lung) organ sites. Based on their affinity for the lactosyl-resin and monosaccharides, LSBPs hold potential for PDAC diagnosis and as drug targets. This work has set the stage for further investigation of the occurrence and the role of LSBPs in patient samples using the newly established workflow.

Sugar-derived oxazolone pseudotetrapeptide as γ-turn inducer and anion-selective transporter

The intramolecular cyclization of a C-3-tetrasubstituted furanoid sugar amino acid-derived linear tetrapeptide afforded an oxazolone pseudo-peptide with the formation of an oxazole ring at the C-terminus. A conformational study of the oxazolone pseudo-peptide showed intramolecular C=O···HN(II) hydrogen bonding in a seven-membered ring leading to a γ-turn conformation. This fact was supported by a solution-state NMR and molecular modeling studies. The oxazolone pseudotetrapeptide was found to be a better Cl--selective transporter for which an anion-anion antiport mechanism was established.

Can Heterocyclic γ-Peptides Provide Polyfunctional Platforms for Synthetic Glycocluster Construction?

Sugars play key roles in many molecular and cellular communication processes involving a family of proteins named lectins. The low affinity associated with sugar recognition is generally counterbalanced by the multivalent nature of the interaction. While many polyglycosylated architectures have been described, only a few studies focused on the impact of topology variations of the multivalent structures on the interaction with lectin proteins. One major interest of our group concerns the design of new highly predictable and stable molecular pseudo-peptide architectures for therapeutic applications. In such a context, we described a class of constrained heterocyclic γ-amino acids built around a thiazole ring, named ATCs. ATC oligomers are helical molecules resulting from the formation of a highly stable C₉ hydrogen-bonding pattern. Following our program, we herein address the potential of ATC oligomers as tunable scaffolds for the development of original multivalent glycoclusters.

Aminooxylated Carbohydrates: Synthesis and Applications

Among other classes of biomolecules, carbohydrates and glycoconjugates are widely involved in numerous biological functions. In addition to addressing the related synthetic challenges, glycochemists have invested intense efforts in providing access to structures that can be used to study, activate, or inhibit these biological processes. Over the past few decades, aminooxylated carbohydrates have been found to be key building blocks for achieving these goals. This review provides the first in-depth overview covering several aspects related to the syntheses and applications of aminooxylated carbohydrates. After a brief introduction to oxime bonds and their relative stabilities compared to related C═N functions, synthetic aspects of oxime ligation and methodologies for introducing the aminooxy functionality onto both glycofuranosyls and glycopyranosyls are described. The subsequent section focuses on biological applications involving aminooxylated carbohydrates as components for the construcion of diverse architectures. Mimetics of natural structures represent useful tools for better understanding the features that drive carbohydrate-receptor interaction, their biological output and they also represent interesting structures with improved stability and tunable properties. In the next section, multivalent structures such as glycoclusters and glycodendrimers obtained through oxime ligation are described in terms of synthetic design and their biological applications such as immunomodulators. The second-to-last section discusses miscellaneous applications of oxime-based glycoconjugates, such as enantioselective catalysis and glycosylated oligonucleotides, and conclusions and perspectives are provided in the last section.

Acyclic αγα-Tripeptides with Fluorinated- and Nonfluorinated-Furanoid Sugar Framework: Importance of Fluoro Substituent in Reverse-Turn Induced Self-Assembly and Transmembrane Ion-Transport Activity

Acyclic αγα-tripeptides derived from fluorinated-furanoid sugar amino acid frameworks act as reverse-turn inducers with a U-shaped conformation, whereas the corresponding nonfluorinated αγα-tripeptides show random peptide conformations. The NMR studies showed the presence of bifurcated weak intramolecular hydrogen bonding (F···HN) and N⁺···F^δ- charge-dipole attraction compel the amide carbonyl groups to orient antiperiplanar to the C-F bond, thus, demonstrating the role of the fluorine substituent in stabilizing the U-shaped conformation. The NOESY data indicate that the U-shaped tripeptides self-assembly formation is stabilized by the intermolecular hydrogen bonding between C═O···HN with antiparallel orientation. This fact is supported by ESI-MS data, which showed mass peaks up to the pentameric self-assembly, even in the gas phase. The morphological analysis by FE-SEM, on solid samples, showed arrangement of fibers into nanorods. The antiparallel self-assembled pore of the fluorinated tripeptides illustrates the selective ion-transport activity. The experimental findings were supported by DFT studies.

N–O linkage in carbohydrates and glycoconjugates

The synthesis and chemical and physicochemical properties as well as biological and medical applications of various hydroxylamine-functionalized carbohydrate derivatives are summarized.