Block synthesis of Forssman pentasaccharide GalNAcα1-3GalNAcβ1-3Galα1-4Galβ1-4Glcβ in the form of 3-aminopropyl glycoside.

A total chemical synthesis of spacer-armed Forssman pentasaccharide is reported. The choice of the 2(donor) + 3(acceptor) block scheme, the optimal combination of a limited number of simple protecting groups and the sequence of deprotection steps allowed to achieve the high yield and stereoselectivity of glycosylation and to avoid losses during deprotection. The target pentasaccharide was obtained in a 10-mg scale.

Destabilization of Glycosyl Cation by an Electron-Withdrawing Substituent at C-5 Makes Sialylation Reaction More α-Stereoselective.

Comparison of the reactivity of sialyl chlorides and bromides based on -acetylneuraminic acid (Neu5Ac) and its deaminated analogue (KDN) in reactions with MeOH and -PrOH without a promoter revealed that the acetoxy group at C-5 in a molecule of a sialic acid glycosyl donor can destabilize the corresponding glycosyl cation making the S1-like reaction pathway unfavorable. A change to the S2-like reaction pathway ensures preferential formation of the α-glycoside.

Antigen Presentation in an Artificial and Cell Membrane: Blood Group A Glycan Recognition.

Glycosphingolipids (GSL) are functionally important components of the cell membrane and recognition of their glycan "head" by the immune system is a key part of normal and pathological processes. Recognition of glycolipid antigens on a living cell, their structure, "context" (microenvironment and clustering), presentation including orientation and distance from the plasma membrane, as well as molecular dynamics are important. GSL antigens are targets for the development of anticancer vaccines and therapeutic antibodies, therefore, control of the presentation of their glycans by synthetic methods opens up new possibilities in medicine.

Stereocontrolled 1,2-trans-arabinofuranosylation in the absence of 2-O-acyl group in glycosyl donor.

Stereocontrolled 1,2-trans-α-arabinofuranosylation using polysilylated mono- and disaccharide glycosyl donors was investigated. A complete α-stereoselectivity of 1,2-trans-arabinofuranosylation was found for Ara-β-(1 → 2)-Ara disaccharide glycosyl donors containing five triisopropylsilyl (TIPS) groups with arylthiol (1) (as shown in our previous publications) or N-phenyltrifluoroacetimidoyl (2) (this work) leaving groups. Conversely, in case of monosaccharide thioglycosides polysilylated with acyclic silyl groups (TIPS, TBDPS), stereoselectivity of glycosylation was lower (α:β = 7-8:1), although the desired α-isomer still dominated.