National Glycoengineering Research Center, Shandong Provincial Key Laboratory of Carbohydrate Chemistry and Glycobiology , Shandong University , Jinan , Shandong 250100 , China.
Department of Chemistry , University of Florida , 214 Leigh Hall , Gainesville , Florida 32611 , United States.
J Org Chem. 2018 Jun 1;83(11):5920-5930. doi: 10.1021/acs.joc.8b00396. Epub 2018 May 10.
The first chemical synthesis of the repeating unit of serotype II group B Streptococcus capsular polysaccharide, a branched heptasaccharide α-Neu p5Ac-(2→3)-β-d-Gal p-(1→4)-β-d-GlcN pAc-(1→3)-{[β-d-Gal p-(1→6)]-β-d-Gal p}-(1→4)-β-d-Glc p-(1→3)-β-d-Glc p-(1→, was achieved by convergent [4+2+1] glycosylation, after probing different synthetic strategies and overcoming a series of difficulties. The title compound was designed to carry a free amino group at its downstream end to enable further regioselective elaboration. This work also revealed that the α-Neu5Ac-(2→3)-β-d-Gal-(1→4)-β-d-GlcNAc motif, which is common in natural glycans, had a low reactivity as glycosyl donors, so it was rather difficult to directly couple this trisaccharide with sterically hindered acceptors. The motif was efficiently constructed via on-site glycan elongation using properly protected GlcN and α-Neu5Ac-(2→3)-β-d-Gal as consecutive glycosyl donors.
乙型流感嗜血杆菌血清型 II 组荚膜多糖重复单元的首次化学合成，一种支化的七糖α-Neu p5Ac-(2→3)-β-d-Gal p-(1→4)-β-d-GlcN pAc-(1→3)-{[β-d-Gal p-(1→6)]-β-d-Gal p}-(1→4)-β-d-Glc p-(1→3)-β-d-Glc p-(1→, 是通过收敛的[4+2+1]糖苷化实现的，在探索了不同的合成策略并克服了一系列困难之后。该标题化合物被设计在其下游末端携带一个游离氨基，以实现进一步的区域选择性修饰。这项工作还表明，在天然糖中常见的α-Neu5Ac-(2→3)-β-d-Gal-(1→4)-β-d-GlcNAc 基序作为糖基供体的反应性较低，因此很难直接将该三糖与空间位阻较大的受体偶联。该基序通过使用适当保护的 GlcN 和α-Neu5Ac-(2→3)-β-d-Gal 作为连续糖基供体，通过现场糖链延伸有效地构建。
