Regio- and stereo-controlled synthesis of β-Xyl(1–4)Rbo-5P1-Rbo, the partial structure of O-mannosyl glycan

Synthesis of Core M3 Matriglycan Constituents via an Additive-Controlled 1,2-cis-Xylopyranosylation with O-Xylosyl Imidates as Donors

A highly stereoselective strategy for 1,2-cis-xylopyranoside bond formation was established via a preactivation-based, additive-modulated trichloroacetimidate glycosidation strategy. The current protocol is mild, practical, and successful with various xylopyranosyl donors and glycosyl acceptors, including acceptors that are reported to be less reactive due to steric hindrance. The utility of this method was demonstrated with the facile assembly of matriglycan constituent tetra- and hexasaccharides.

Chemical and Chemo-Enzymatic Syntheses of Glycans Containing Ribitol Phosphate Scaffolding of Matriglycan

Ribitol phosphate modifications to the core M3 O-mannosyl glycan are important for the functional maturation of α-dystroglycan. Three sequentially extended partial structures of the core M3 O-mannosyl glycan including a tandem ribitol phosphate were regio- and stereo-selectively synthesized: Rbo5P-3GalNAcβ, Rbo5P-1Rbo5P-3GalNAcβ, and Xylβ1-4Rbo5P-1Rbo5P-3GalNAcβ (Rbo5P, d-ribitol-5-phosphate; GalNAc, N-acetyl-d-galactosamine; Xyl, d-xylose). Rbo5P-3GalNAcβ with p-nitrophenyl at the aglycon part served as a substrate for ribitol phosphate transferase (FKRP, fukutin-related protein), and its product was glycosylated by the actions of a series of glycosyltransferases, namely, ribitol xylosyltransferase 1 (RXYLT1), β1,4-glucuronyltransferase 1 (B4GAT1), and like-acetyl-glucosaminyltransferase (LARGE). Rbo5P-3GalNAcβ equipped with an alkyne-type aglycon was also active for FKRP. The molecular information obtained on FKRP suggests that Rbo5P-3GalNAcβ derivatives are the minimal units required as the acceptor glycan for Rbo5P transfer and may serve as a precursor for the elongation of the core M3 O-mannosyl glycan.

Stereo- and Regioselective Synthesis of O-Mannosyl Glycan Containing Matriglycan and a Part of Tandem Ribitol Phosphate

We herein successfully synthesized two pivotal structures of O-mannosyl glycan: (1) the matriglycan-repeating tetrasaccharide Xylα1-3GlcAβ1-3Xylα1-3GlcAβ and (2) the link between matriglycan and a part of tandem ribitol phosphate, Xylα1-3GlcAβ1-4Xylβ1-4Rbo, in a regio- and stereocontrolled manner. The disaccharide unit with the α-linkage of xylose was obtained by adopting the conformational fixation of the xylopyranoside ring and a specific solvation system of diastereoselective solubility.