Synthesis and conformational behavior of the difluoromethylene linked C-glycoside analog of beta-galactopyranosyl-(1<-->1)-alpha-mannopyranoside

Comparison of Conformational Analyses of Naturally Occurring Flavonoid-O-Glycosides with Unnatural Flavonoid-CF2-Glycosides Using Molecular Modeling

Many glycosylated natural products display biological activity and are deglycosylated by the metabolic processes of the body. Although unnatural CF2-glycosides have been proposed as nonhydrolyzable analogues, CF2-derivatives of natural products are exceedingly challenging to synthesize and few examples exist. These difluorinated molecules may have unique conformational behavior as a consequence of changing the glycosidic linkage. In this study, we performed conformational searches using MacroModel followed by molecular dynamics simulations to investigate the conformational behavior of the glycosidic bonds in flavonoid-O-glycosides and in corresponding CF2-glycosylated derivatives. Compared to their O-glycosylated analogues, flavonoid-3-CF2-glycosides and flavonoid-5-CF2-glycosides showed conformational bias, whereas flavonoid-7-CF2-glycosides showed more flexibility. Flavonoid-5-CF2-glycosides were the least flexible compared to all others. Our results show that the site of the glycosylation and the substitution pattern on the flavonoid determine the conformational properties of these molecules. These two factors influence the steric destabilization and/or stereoelectronic stabilization which govern the conformational behavior of the flavonoid glycosides. Moreover, a docking study of quercitrin and its CF2-analogue into murine ribosomal kinase RSK2 demonstrated the potential for flavonoid-CF2-glycosides to retain a similar binding pose as the parent O-glycoside. These findings will assist in designing stable flavonoid-CF2-glycosides for carbohydrate research.

Ganglioside GM3 Analogues Containing Monofluoromethylene-Linked Sialoside: Synthesis, Stereochemical Effects, Conformational Behavior, and Biological Activities

Glycoconjugates are an important class of biomolecules that regulate numerous biological events in cells. However, these complex, medium-size molecules are metabolically unstable, which hampers detailed investigations of their functions as well as their potential application as pharmaceuticals. Here we report sialidase-resistant analogues of ganglioside GM3 containing a monofluoromethylene linkage instead of the native O-sialoside linkage. Stereoselective synthesis of CHF-linked disaccharides and kinetically controlled Au(I)-catalyzed glycosylation efficiently furnished both stereoisomers of CHF-linked as well as CF ₂ - and CH ₂ -linked GM3 analogues. Like native GM3, the C-linked GM3 analogues inhibited the autophosphorylation of epidermal growth factor (EGF) receptor induced by EGF in vitro. Assay of the proliferation-enhancing activity toward Had-1 cells together with NMR-based conformational analysis showed that the (S)-CHF-linked GM3 analogue with exo-gauche conformation is the most potent of the synthesized compounds. Our findings suggest that exo-anomeric conformation is important for the biological functions of GM3.

Fluorinated carbohydrates as chemical probes for molecular recognition studies. Current status and perspectives

This review provides an extensive summary of the effects of carbohydrate fluorination with regard to changes in physical, chemical and biological properties with respect to regular saccharides. The specific structural, conformational, stability, reactivity and interaction features of fluorinated sugars are described, as well as their applications as probes and in chemical biology.

Versatile Glycosyl Sulfonates in β-Selective C-Glycosylation

C-Glycosides are both a common motif in many bioactive natural products and important glycoside mimetics. We demonstrate that activating a hemiacetal with a sulfonyl chloride, followed by treating the resultant glycosyl sulfonate with an enolate results in the stereospecific construction of β-linked C-glycosides. This reaction tolerates a range of acceptors and donors, including disaccharides. The resulting products can be readily derivatized into C-glycoside analogues of β-glycoconjugates, including C-disaccharide mimetics.

Acyl Glycosides through Stereospecific Glycosyl Cross-Coupling: Rapid Access to C(sp3)-Linked Glycomimetics

Replacement of a glycosidic bond with hydrolytically stable C-C surrogates is an efficient strategy to access glycomimetics with improved physicochemical and pharmacological properties. We describe here a stereoretentive cross-coupling reaction of glycosyl stannanes with C(sp2)- and C(sp3)-thio(seleno)esters suitable for the preparation C-acyl glycosides as synthetic building blocks to obtain C(sp3)-linked and fluorinated glycomimetics. First, we identified a set of standardized conditions employing a Pd(0) precatalyst, CuCl additive, and phosphite ligand that provided access to C-acyl glycosides without deterioration of anomeric integrity and decarbonylation of the acyl donors (>40 examples). Second, we demonstrated that C(sp3)-glycomimetics could be introduced into the anomeric position via a direct conversion of C1 ketones. Specifically, the conversion of the carbonyl group into a CF2 mimetic is an appealing method to access valuable fluorinated analogues. We also illustrate that the introduction of other carbonyl-based groups into the C1 position of mono- and oligosaccharides can be accomplished using the corresponding acyl donors. This protocol is amenable to late-stage glycodiversification and programmed mutation of the C-O bond into hydrolytically stable C-C bonds. Taken together, stereoretentive anomeric acylation represents a convenient method to prepare a diverse set of glycan mimetics with minimal synthetic manipulations and with absolute control of anomeric configuration.

Studies on the synthesis of a sugar triazole based ligand for protein and DNA binding

Bis-triazole derivatives accomplished by [3 + 2] cycloaddition methodology were well characterized. Interaction of bis-triazoles with BSA and CT-DNA had good correlation with experimental and docking studies. Compounds showed moderate to excellent antibacterial activity.

Addition of electrophilic radicals to 2-benzyloxyglycals: synthesis and functionalization of fluorinated α-C-glycosides and derivatives

A new method for the synthesis of fluorinated α-C-glycosides is described. The reactions between highly electrophilic radicals (fluorinated or unfluorinated) and a 2-benzyloxyglucal or galactal provide 2-keto-D-arabino- or 2-keto-D-lyxo-hexopyranosides through an addition/fragmentation process. Sodium borohydride mediated or Meerwein-Ponndorf-Verley (MPV) reduction of these compounds provides α-C-glycosides that feature appropriate anchoring groups for further synthetic elaboration. The presence of CF2 CO2 iPr or CF2 Br groups at the pseudo-anomeric position allows efficient reduction/olefination or Br/Li-exchange/nucleophilic-addition sequences. These transformations open the way for the synthesis of fluorinated C-glycosidic analogues of glycoconjugates.

Synthesis of fluorinated C-mannopeptides as sialyl Lewisx mimics for E- and P-selectin inhibition

The synthesis of fluorinated C-mannopeptides and their evaluation as E- and P-selectin inhibitors is described. These molecules are difluorinated analogues of CH(2)-glycopeptides already reported to act as sLe(x) mimics. The alpha and beta anomers of these CF(2)-glycopeptides have been prepared, as well as their 1-hydroxy analogues which were present in solution as an equilibrium mixture of alpha- and beta-pyranose and alpha- and beta-furanose forms. These molecules showed inhibitory activities comparable to their CH(2) counterparts with a moderate influence of the pseudo-anomeric center configuration.

A strategy for constructing C-sialosides based on Ireland-Claisen rearrangement and its application for synthesis of CF2-linked ganglioside GM4 analog

Sialidase-resistant ganglioside analogs having similar biological activities to natural gangliosides are expected to be important probes for clarifying the biological functions of gangliosides. Focusing on difluoromethylene-linked (CF2-linked) and methylene-linked (CH2-linked) α(2,3)sialylgalactose as a core structure of sialidase-resistant ganglioside mimics, we have developed novel, stereocontrolled, and efficient methodologies to synthesize C-sialosides based on Ireland-Claisen rearrangement. These methods were employed to synthesize CF2-linked GM4. The CF2-linked GM4 inhibited human sialidases NEU2 and NEU4 with IC50 values of 754 and 930 μM, respectively, and strongly inhibited human lymphocyte proliferation in the same concentration range as natural GM4.