Synthesis of β-galactosylamides as ligands of the peanut lectin. Insights into the recognition process

Synthesis of N-glycosyl amides: conformational analysis and evaluation as inhibitors of β-galactosidase from E. coli

The synthesis of N-glycosyl amides typically involves the use of glycosyl amines as direct precursors, resulting in low yields due to hydrolysis and the loss of stereocontrol through anomerization processes. In this study, a sequential synthesis of N-glycosyl amides is proposed, employing glycosyl amines as intermediates obtained from glycosyl azides. Derivatives with gluco, galacto, or xylo configurations were synthesized. Hexose derivatives were obtained under stereocontrol to give only the β anomer, while the xylo derivatives provided a mixture of α and β anomers. Conformational analysis revealed that all β anomers adopted the 4C1 conformation, while α anomers were found in the 1C4 chair as the major conformer. After de-O-acetylation, the derivatives containing a galactose unit were evaluated as inhibitors of β-galactosidase from E. coli and were found to be moderate inhibitors.

Stereoselective synthesis of glycosyl azides from anomeric hydroxides via protecting group manipulations

Herein, we report the direct conversion of anomeric hydroxides to glycosyl azides in one step using diphenylphosphoryl azide. Protecting group manipulations on the hexose sugars have enabled the stereoselective synthesis of either the α-glycosyl azides or the β-anomeric azides in moderate to very good yields. The reaction has also been successfully used to enable the synthesis of β-2-deoxy-2-aminoglucosyl azides.

A Sub-Micromolar MraYAA Inhibitor with an Aminoribosyl Uridine Structure and a (S,S)-Tartaric Diamide: Synthesis, Biological Evaluation and Molecular Modeling

New inhibitors of the bacterial tranferase MraY are described. Their structure is based on an aminoribosyl uridine scaffold, which is known to be important for the biological activity of natural MraY inhibitors. A decyl alkyl chain was introduced onto this scaffold through various linkers. The synthesized compounds were tested against the MraY_AA transferase activity, and the most active compound with an original (S,S)-tartaric diamide linker inhibits MraY activity with an IC₅₀ equal to 0.37 µM. Their antibacterial activity was also evaluated on a panel of Gram-positive and Gram-negative strains; however, the compounds showed no antibacterial activity. Docking and molecular dynamics studies revealed that this new linker established two stabilizing key interactions with N190 and H325, as observed for the highly potent inhibitors carbacaprazamycin, muraymycin D2 and tunicamycin.

The disulfide bond as a key motif for the construction of multivalent glycoclusters

S-Glycosylated dendrons having a thioacetate group in their focal points led to multivalent glycoclusters by spontaneous O2-oxidation of sulfides.

Expression of Thomsen-Friedenreich Antigen in Colorectal Cancer and Association with Microsatellite Instability

Microsatellite instability (MSI) is a molecular phenotype due to a deficient DNA mismatch repair (dMMR). In colorectal cancer (CRC), dMMR/MSI is associated with several clinical and histopathological features, influences prognosis, and is a predictive factor of response to therapy. In daily practice, dMMR/MSI profiles are identified by immunohistochemistry and/or multiplex PCR. The Thomsen-Friedenreich (TF) antigen was previously found to be a potential single marker to identify MSI-high gastric cancers. Therefore, in this study, we aimed to disclose a possible association between TF expression and MSI status in CRC. Furthermore, we evaluated the relationship between TF expression and other clinicopathological features, including patient survival. We evaluated the expression of the TF antigen in a cohort of 25 MSI-high and 71 microsatellite stable (MSS) CRCs. No association was observed between the expression of the TF antigen and MSI-high status in CRC. The survival analysis revealed that patients with MSI-high CRC showed improved survival when the TF antigen was expressed. This finding holds promise as it indicates the potential use of the TF antigen as a biomarker of better prognosis in MSI-high CRCs that should be validated in an independent and larger CRC cohort.

Photocatalyzed reductive fluoroalkylation of 2-acetoxyglycals towards the stereoselective synthesis of α-1-fluoroalkyl-C-glycosyl derivatives

A benign, efficient, regio- and stereoselective protocol for the syntheses of α-1-fluoroalkyl-C-glycosyl compounds bearing CF3, C4F9, and C6F13 substituents on the anomeric carbon has been developed by a new methodology starting from 2-acetoxyglycals for the first time. Remarkably, the reactions proceeded in only one step, through the visible light-photocatalyzed reductive fluoroalkylation of 2-acetoxyglycals by means of an Ir photocatalyst and employed commercially available fluoroalkyl iodides n-CnF2n+1-I (n = 1, 4, 6) as a source of fluoroalkyl radicals.

Crystal structures of peanut lectin in the presence of synthetic β-N- and β-S-galactosides disclose evidence for the recognition of different glycomimetic ligands

Carbohydrate-lectin interactions are involved in important cellular recognition processes, including viral and bacterial infections, inflammation and tumor metastasis. Hence, structural studies of lectin-synthetic glycan complexes are essential for understanding lectin-recognition processes and for the further design of promising chemotherapeutics that interfere with sugar-lectin interactions. Plant lectins are excellent models for the study of the molecular-recognition process. Among them, peanut lectin (PNA) is highly relevant in the field of glycobiology because of its specificity for β-galactosides, showing high affinity towards the Thomsen-Friedenreich antigen, a well known tumor-associated carbohydrate antigen. Given this specificity, PNA is one of the most frequently used molecular probes for the recognition of tumor cell-surface O-glycans. Thus, it has been extensively used in glycobiology for inhibition studies with a variety of β-galactoside and β-lactoside ligands. Here, crystal structures of PNA are reported in complex with six novel synthetic hydrolytically stable β-N- and β-S-galactosides. These complexes disclosed key molecular-binding interactions of the different sugars with PNA at the atomic level, revealing the roles of specific water molecules in protein-ligand recognition. Furthermore, binding-affinity studies by isothermal titration calorimetry showed dissociation-constant values in the micromolar range, as well as a positive multivalency effect in terms of affinity in the case of the divalent compounds. Taken together, this work provides a qualitative structural rationale for the upcoming synthesis of optimized glycoclusters designed for the study of lectin-mediated biological processes. The understanding of the recognition of β-N- and β-S-galactosides by PNA represents a benchmark in protein-carbohydrate interactions since they are novel synthetic ligands that do not belong to the family of O-linked glycosides.

Chirality inversion, supramolecular hydrogelation and lectin binding of two thiolactose amphiphiles constructed on a di-lauroyl-l-tartaric acid scaffold

The supramolecular self-assembly mode of two diacyl-glycoamphiphiles depends on the length of the flexible achiral ethoxylated linker.