Synthesis of sialic acid-lipid conjugates and their neuritogenic effects on N1E.115 neuroblastoma cells

Step-economy synthesis of β-steryl sialosides using a sialyl iodide donor

Steryl glycosides are prevalent in nature and have unique biological activities dictated by sterol structure, sugar composition, and the stereochemical attachment of the aglycone. A single configurational switch can have profound biological consequences meriting the systematic study of structure and function relationships. Steryl congeners of N-acetyl neuraminic acid (NANA) impact neurobiological processes and may also mediate host/microbe interactions. In order to study these processes, a platform for the synthesis of β-steryl sialosides has been established. Promoter-free glycosidations using a novel α-linked sialyl iodide donor efficiently provide unique amphiphilic sialoglycoconjugates for examining bioactivities in various systems.

Chemical Synthesis of Glycosides of N-Acetylneuraminic Acid

Investigations of methodologies aimed on improving the stereoselective synthesis of sialosides and the efficient assembly of sialic acid glycoconjugates has been the mission of dedicated research groups from the late 1960s. This review presents major accomplishments in the field, with the emphasis on significant breakthroughs and influential synthetic strategies of the last decade.

Syntheses of new peptidic glycoclusters derived from β-alanine: di- and trimerized glycoclusters and glycocluster–clusters

Fluorescence-labeled glycoclusters 1 and 2 have been synthesized to elongate glycocluster units that contain beta-alanine derivative 6 and sugar unit 7. Similarly, di- and trimerized glycoclusters 3 and 4 have been obtained by coupling glycocluster 17 with succinyl chloride and/or trimesoyl chloride, respectively. Furthermore, glycocluster-cluster 5 was also synthesized by a convergent growth approach.

Solid-phase synthesis of multiantennary oligonucleotide glycoconjugates utilizing on-support oximation

A novel method for preparation of multivalent oligonucleotide glycoconjugates on a solid support has been described. A pentaerythritol-based phosphoramidite (1) bearing two masked aminooxy groups has been used as the key building block. After conventional chain assembly, the aminooxy functions have been deblocked by a hydrazinium acetate treatment and subsequently oximated with fully acetylated 4-oxobutyl alpha-D-mannopyranoside. The conjugates obtained have been shown to withstand standard ammonolytic deprotection and cleavage from the support. Four different oligonucleotide glycoconjugates containing two, four, or six alpha-D-mannopyranosyl units (12-15) have been prepared to demonstrate the applicability of the procedure. The glycosyl residues only moderately retards hybridization of the oligonucleotide moiety.

Solid-phase synthesis of oligonucleotide glycoconjugates bearing three different glycosyl groups: orthogonally protected bis(hydroxymethyl)-N,N'-bis(3-hydroxypropyl)malondiamide phosphoramidite as key building block

Diethyl O,O'-(methoxymethylene)bis(hydroxymethyl)malonate (3) was observed to undergo a stepwise aminolysis when treated with 3-aminopropanol. This allowed convenient preparation of bis(hydroxymethyl)-N,N'-bis(3-hydroxypropyl)malondiamide bearing orthogonal levulinyl (Lev) and tert-butyldiphenylsilyl (TBDPS) protections at the two N-hydroxypropyl groups (8). One of the hydroxylmethyl functions was then protected with a 4,4'-dimethoxytrityl (DMTr) group, and the other one was phosphitylated to obtain a methyl N,N-diisopropylphosphoramidite (1). This building block was used for the synthesis of oligonucleotide glycoconjugates (25 and 26) carrying three different sugar units. After conventional phosphoramidite chain assembly of the sequence containing 1, the 5'-terminal DMTr group was removed and an appropriate glycosyl 6-O-phosphoramidite was coupled. The remaining protections of the branching unit were removed in the order of Lev and TBDPS, and the exposed hydroxyl functions were reacted one after another with the desired glycosyl 6-O-phosphoramidites. Global deprotection and cleavage of the conjugate from the support were achieved by conventional ammonolysis.

Carbohydrate natural products as a scaffolding for the preparation of potential neuraminidase inhibitors

Compound 10b, 6-acetamido-6,8-dideoxy-D-erythro-beta-D- galacto-octopyranosyl-1-oxyacetic acid sodium salt, was synthesised by hydrazinolysis of Lincomycin, acetylation of methylthiolincosaminide (MTL) 9a, and by subsequent glycosylation of acetate 9b with methyl glycolate under mild conditions (NIS/TfOH). The methyl ester 10a was hydrolysed by treatment with Amberlite Ira-4OO (OH-) resin and aqueous sodium hydroxide, followed by neutralisation with Dowex-50 W x 8 (H+) resin and lyophilisation to give 10b. This carboxylate may represent the first derivative in a novel series of sialidase inhibitors utilising carbohydrate natural products. The phosphonate 11c, prepared under the same experimental conditions with dibenzyl(hydroxymethyl)phosphonate as acceptor, also displays an inhibitory activity towards Clostridium perfringens sialidase (Ki in mM range as with Neu5Ac).

Synthesis and application of alpha-D-mannosyl clusters as photoaffinity ligands for mannose-binding proteins: concanavalin A as a model receptor

Mono-, di-, and tri-antennary alpha-D-mannopyranosyl derivatives were synthesized as oligosaccharide mimics. The compounds vary in the length of the acyclic aglyconic spacers linking, in the case of the di- and tri-antennary derivatives, the glycosyl endgroups. By haemagglutination assay (Coombs test) the affinity of the alpha-D-mannopyranosyl ligands against Con A was determined in comparison with methyl alpha-D-mannopyranoside. Affinity enhancement and strong cross-linking capacity were found with the di- and tri-antennary compounds where alpha-D-mannopyranosyl endgroups are separated by spacers of 5-37 atoms in length. The optimal ligand had Ki of 5.1 microM in comparison with 3.12 microM for methyl alpha-D-mannopyranoside. The monoantennary compound and, to certain extents, one di- and short tri-antennary ligands with short spacer lengths did not differ significantly in affinity from methyl alpha-D-mannopyranoside. A triantennary, radiolabelled ligand equipped with a photolabile diazirino group was used to covalently modify Con A by photoaffinity labelling. A significant degree of covalent cross-linking of Con A monomers was observed.