Unified Strategy toward Stereocontrolled Assembly of Various Glucans Based on Bimodal Glycosyl Donors

Abstract

Polymers of glucose, the most abundant and one of the biologically important natural products, named glucans are widely present in fungi, bacteria, mammals, and plants with various anomeric configurations and glycosidic linkages. Because of their structural diversity, the unified strategy for the assembly of pure glucans is yet to be developed. Herein, we describe a general strategy that is applicable to construction of all types of glucans by exploiting a bimodal glycosyl donor equipped with C2-o-TsNHbenzyl ether (TAB), which enables stereocontrolled synthesis of both α- and β-glycosides by switching reaction conditions.

Chemical Synthesis and Evaluation of Exopolysaccharide Fragments Produced by <i>Leuconostoc mesenteroides</i> Strain NTM048

“…A variety of glycosylation reactions have been developed to construct the α-linkage and have been applied to the synthesis of α-glucan oligomers. 9,10) Although the synthesis of similar linear α-(1→ 6)-linked oligomers was reported by several groups, [11][12][13][14][15][16][17] the facile synthesis of oligomers containing an α-(1→ 3)-branched structure is still limited. 14,17) We synthesized tetrasaccharide 2 (Chart 1), following the strategy reported by Lam and Gervay-Hague 12,13) where the α-(1→ 6)-linked glucosyl oligomers were synthesized using 6-O-acetyl-2,3,4-tri-O-benzylglucopyranosyl iodide as a glycosyl donor.…”

“…9,10) Although the synthesis of similar linear α-(1→ 6)-linked oligomers was reported by several groups, [11][12][13][14][15][16][17] the facile synthesis of oligomers containing an α-(1→ 3)-branched structure is still limited. 14,17) We synthesized tetrasaccharide 2 (Chart 1), following the strategy reported by Lam and Gervay-Hague 12,13) where the α-(1→ 6)-linked glucosyl oligomers were synthesized using 6-O-acetyl-2,3,4-tri-O-benzylglucopyranosyl iodide as a glycosyl donor. 18,19) The precursor acetate 5 for glycosyl iodide 6 was prepared from the commercially available methyl α-Dglucopyranoside 4.…”

Bimodal Glycosyl Donors as an Emerging Approach Towards a General Glycosylation Strategy

“…The same authors later published results demonstrating the advantage of a bimodal approach to complex oligosaccharide construction. [21] Using just three imidate donors 21, 22 and 23 with different protecting group patterns (Figure 10a), both linear and branched oligosaccharides were synthesised with high stereocontrol over each glycosidic bond. The same donor 21 was used to construct the tetramaltosides 24 and 25 with either all αor all β-(1!6)-linkages (Figure 10b).…”

Recent Progress in 1,2-cis glycosylation for Glucan Synthesis

“…Based on basic observations, the solvent effect [174][175][176][177][178][179][180], the concentration effect [181][182][183][184][185], and other factors [186][187][188], including a very recent approach using an S N 2-predicting, leaving group enhanced by a coordinating acceptor [189,190], were also accepted as factors for the stereoselectivity of glycosylation. This review focuses on two effective and stereoselective methods for glucan synthesis: the use of C2-o-tosylamide (TsNH)-benzyl (TAB) ether for bimodal glycosylation [191][192][193] and ZnI 2 -mediated 1,2-cis glycosylation [194].…”