Yuko Shingu

An easy access to halide ion-catalytic α-glycosylation using carbon tetrabromide and triphenylphosphine as multifunctional reagents

The reaction of a 2-O-benzyl-1-hydroxy sugar with CBr4 and Ph3P generates a glycosyl bromide in situ, which is coupled with an acceptor alcohol in the presence of N,N-tetramethylurea to afford an alpha-glycosyl product virtually quantitatively. In a proposed pathway, the reagent combination plays multiple roles such as the generation of a glycosyl donor, the activation of glycosylation, and the dehydration of the reaction system. These roles allow a simple alpha-glycosylation to be performed without special attention to dehydration. Various alpha-glycosyl (D-gluco-, D-galacto- and L-fuco-) products including glycosyl glycerols and cholesterols have been prepared with this method.

Synthesis and absolute structures of Mycoplasma pneumoniae β-glyceroglycolipid antigens

Just recently, a pair of beta-glycolipids was isolated from the cell membrane of Mycoplasma pneumoniae as a mixture of the two compounds. They are the major immunodeterminants of this pathogenic Mycoplasma and indicate high medicinal potential. They have a beta-(1-->6)-linked disaccharide structure close to each other; one has beta-d-galactopyranoside (beta-Gal-type 1) at the non-reducing terminal, and another has beta-d-glucopyranoside (beta-Glc-type 2). In the present study, the first stereoselective synthesis was conducted for each of the two beta-glycolipids 1 and 2. (1)H NMR and TLC-immunostaining studies of the synthetic compounds enable us to establish the absolute structures having the beta-(1-->6)-linked disaccharides at the glycerol sn-3 position.

CONVENIENT ACCESS TO HALIDE ION-CATALYZED α-GLYCOSYLATION FREE FROM NOXIOUS FUMES AT THE DONOR SYNTHESIS

a-Selective glycosylation is a highly challenging and meaningful objective in carbohydrate chemistry. This is mainly because many biologically active oligosaccharides and other glycoconjugates in nature carry an a-glycoside linkage at the non-reducing terminal such as a-L-fucoside in sialyl Lewis antigens and a-D-galactobioside in P antigens. However, a-glycosylation is not straightforward and requires optimization of the glycosyl donors, promoters, solvents, and other reaction conditions. In this respect, a halide ion-catalyzed a-glycosylation method proposed by Lemieux et al. in 1975 has provided one of the few definitive ways. a-Selectivity is nearly perfect for many acceptor sugars so far examined as long as 2-O-benzyl glycosyl bromides are employed as donors. – d] Moreover, the method requires no heavy metal promoters or strong Lewis acid catalysts. These properties are of high significance for large-scale production of ‘‘sugar-based’’ therapeutic agents and biochemical materials. In our study on the structure and immunogenic activity of a-D-glucopyranosyl-snglycerophospholipids (GGPLs) isolated from Mycoplasma fermentans, we applied

An easy α-glycosylation methodology for the synthesis and stereochemistry of mycoplasma α-glycolipid antigens

Summary Mycoplasma fermentans possesses unique α-glycolipid antigens (GGPL-I and GGPL-III) at the cytoplasm membrane, which carry a phosphocholine group at the sugar primary (6-OH) position. This paper describes a practical synthetic pathway to a GGPL-I homologue (C16:0) and its diastereomer, in which our one-pot α-glycosylation method was effectively applied. The synthetic GGPL-I isomers were characterized with 1H NMR spectroscopy to determine the equilibrium among the three conformers (gg, gt, tg) at the acyclic glycerol moiety. The natural GGPL-I isomer was found to prefer gt (54%) and gg (39%) conformers around the lipid tail, while adopting all of the three conformers with equal probability around the sugar position. This property was very close to what we have observed with respect to the conformation of phosphatidylcholine (DPPC), suggesting that the Mycoplasma glycolipids GGPLs may constitute the cytoplasm fluid membrane together with ubiquitous phospholipids, without inducing stereochemical stress.