Alberta Glycomics Centre and Department of Chemistry, The University of Alberta, Edmonton, Alberta T6G 2G2, Canada.
J Org Chem. 2012 Nov 2;77(21):9826-32. doi: 10.1021/jo301393s. Epub 2012 Oct 17.
Previous studies have demonstrated that cell wall arabinogalactan from mycobacteria possesses a single galactosamine (GalN) residue. This moiety, which is one of the rare natural occurrences of galactosamine lacking an acetyl group on the nitrogen, has been identified as a pendant substituent attached to a highly branched arabinofuranose residue in the arabinan core. However, the stereochemistry by which the GalN residue is linked to the polysaccharide remains unknown. We report here the synthesis of two tetrasaccharides, 1 and 2, consisting of GalN attached through either an α- or β-linkage to a trisaccharide fragment of mycobacterial arabinan. These molecules represent the first synthetic GalN-containing oligosaccharides, and the preparation of both targets was achieved from a single donor species by modulation of the reaction solvent. Comparison of the NMR spectra of 1 and 2 with those obtained from a sample derived from the natural glycan revealed that the GalN residue in the polysaccharide is attached via an α-linkage.
先前的研究表明，分枝杆菌细胞壁阿拉伯半乳聚糖含有单个半乳糖胺（GalN）残基。这种部分是自然界中罕见的不带氮乙酰基的半乳糖胺之一，已被鉴定为连接到阿拉伯呋喃糖残基上的高度支化阿拉伯聚糖核心中的侧基取代基。然而，GalN 残基与多糖连接的立体化学结构仍然未知。我们在这里报告了两种四糖 1 和 2 的合成，它们分别通过α-或β-连接到分枝杆菌阿拉伯聚糖的三糖片段上。这些分子代表了第一个含有 GalN 的合成寡糖，并且这两个目标物的制备都是从单一供体物种通过调节反应溶剂来实现的。1 和 2 的 NMR 谱与从天然糖中获得的样品的 NMR 谱进行比较表明，多糖中的 GalN 残基通过α-键连接。
