Pd-catalyzed coupling reactions of anhydro-aldose tosylhydrazones with aryl bromides to produce substituted exo-glycals

Synthesis of Five-Membered exo-Glycals from Six-Membered 2-Iodo-endo-glycals

Five-membered exo-glycals were synthesized from six-membered 2-iodo-endo-glycals by a metal/halogen exchange/ring-opening sequence followed by a cyclization catalyzed by Ag₂CO₃.

Coupling Reactions of Anhydro-Aldose Tosylhydrazones with Boronic Acids

A catalyst-free coupling reaction between O-peracetylated, O-perbenzoylated, O-permethylated, and O-permethoxymethylated 2,6-anhydro-aldose tosylhydrazones (C-(β-d-glycopyranosyl)formaldehyde tosylhydrazones) and aromatic boronic acids is reported. The base-promoted reaction is operationally simple and exhibits a broad substrate scope. The main products in most of the transformations were open-chain 1-C-aryl-hept-1-enitol type compounds while the expected β-d-glycopyranosylmethyl arenes (benzyl C-glycosides) were formed in subordinate yields only. A mechanistic rationale is provided to explain how a complex substrate may change the well-established course of the reaction.

Stereoselective Palladium-Catalyzed Arylation of Exo-Glycals with Aryl Iodides

A novel methodology for the arylation of exo-glycals has been developed. A range of exo-glycals underwent reactions with aryl iodides in the presence of a palladium catalyst. The transformation proceeded in a stereoselective manner to afford Z-isomers. The developed transformation demonstrated excellent functional group tolerance.

Coupling of N-tosylhydrazones with tetrazoles: synthesis of 2-β-D-glycopyranosylmethyl-5-substituted-2H-tetrazole type glycomimetics

Coupling reactions of O-peracylated 2,6-anhydro-aldose tosylhydrazones (C-(β-d-glycopyranosyl)formaldehyde tosylhydrazones) with tetrazoles were studied under metal-free conditions using thermic or microwave activation in the presence of different bases. The reactions proved highly regioselective and gave the corresponding, up-to-now unknown 2-β-d-glycopyranosylmethyl-2H-tetrazoles in 7-67% yields. The method can be applied to get new types of disaccharide mimetics, 5-glycosyl-2-glycopyranosylmethyl-2H-tetrazoles, as well. Galectin binding studies with C-(β-d-galactopyranosyl)formaldehyde tosylhydrazone and 2-(β-d-galactopyranosylmethyl)-5-phenyl-2H-tetrazole revealed no significant inhibition of any of these lectins.

Stereoselective Synthesis of Ribofuranoid exo-Glycals by One-Pot Julia Olefination Using Ribofuranosyl Sulfones

One-pot Julia olefination using ribofuranosyl sulfones is described. The α-anomers of the ribofuranosyl sulfones were synthesized with complete α-selectivity via the glycosylation of heteroarylthiols using ribofuranosyl iodides as glycosyl donors and the subsequent oxidation of the resulting heteroaryl 1-thioribofuranosides with magnesium monoperphthalate (MMPP). The Julia olefination of the α-ribofuranosyl sulfones with aldehydes proceeded smoothly in one pot to afford the thermodynamically less stable (E)-exo-glycals with modest-to-excellent stereoselectivity (up to E/Z = 94:6) under the optimized conditions. The E selectivity was especially high for aromatic aldehydes. In contrast, the (Z)-exo-glycal was obtained as the main product with low stereoselectivity when the corresponding β-ribofuranosyl sulfone was used (E/Z = 41:59). The remarkable impact of the anomeric configuration of the ribofuranosyl sulfones on the stereoselectivity of the Julia olefination has been rationalized using density functional theory (DFT) calculations. The protected ribose moiety of the resulting exo-glycals induced completely α-selective cyclopropanation on the exocyclic carbon-carbon double bond via the Simmons-Smith-Furukawa reaction. The 2-cyanoethyl group was found to be useful for the protection of the exo-glycals, as it could be removed without affecting the exocyclic C═C bond.

Synthetic Route to Glycosyl β-1C-(phosphino)-phosphonates as Unprecedented Stable Glycosyl Diphosphate Analogs and Their Preliminary Biological Evaluation

The synthesis of glycosyl-β-1C-(phosphino)-phosphonates is a challenge since it has not yet been described. In this paper, we report an innovative synthetic method for their preparation from Glc-, Man-, and GlcNAc- lactone derivatives. The proposed original strategy involves the addition of the corresponding δ-hexonolactones onto the dianion of (methylphosphino) phosphonate as a key step, followed by dehydration and stereoselective addition of dihydrogen on the resulting double bond. Final deprotection provides the new glycosyl diphosphate analogs in 35%, 36%, and 10% yield over 6 steps from the corresponding δ-hexonolactones. The synthetized compounds were evaluated as inhibitors of phosphatase and diphosphatase activities and found to have complex concentration-dependent activatory and inhibitory properties on alkaline phosphatase. The synthetized tools should be useful to study other enzymes such as transferases.

New syntheses towards C-glycosyl type glycomimetics

Glycomimetics are compounds that resemble carbohydrate molecules in their chemical structure and/or biological effect. A large variety of compounds can be designed and synthesized to get glycomimetics, however, C-glycosyl derivatives represent one of the most frequently studied subgroup. In the present survey syntheses of a range of five- and six membered C-glycopyranosyl heterocycles, anhydro-aldimine type compounds, exo-glycals, C-glycosyl styrenes, carbon-sulfur bonded oligosaccharide mimics are described. Some of the C-glycopyranosyl azoles, namely 1,2,4-triazoles and imidazoles belong to the most efficient glucose analog inhibitors of glycogen phosphorylase known to date. Biological studies revealed the therapeutical potential of such inhibitors. Other synthetic derivatives offer versatile possibilities to get further glycomimetics.