We present here a novel concept for the synthesis of branched N-acetyllactosamine (LacNAc) glycan structures. Through a combination of sequential enzymatic and chemical reactions of Leloir-glycosyltransferases, galactose oxidase and reductive amination, we obtained branched glycan oligomers with a variation of LacNAc and/or N′,N′′-diacetyllactosamine (LacdiNAc) glycan epitopes. Incorporation of a branching point was accomplished by an optimized galactose oxidase protocol rendering the C-6 aldehyde functionality at the terminal galactose of a LacNAc oligomer. After glycan chain elongation by glycosyltransferases, the C-6 aldehyde-containing linear building block was conjugated with amine-linker functionalized glycans. Methanol and a temperature of 50 °C were found to be optimum conditions for the α-picoline borane-catalyzed reductive amination. Chemically branched glycans were obtained in high synthetic yields (≈81%) in preparative batches. Product isolation was accomplished by preparative HPLC with good overall yields (>60%). The structural integrity was proven by ESI-MS and NMR. The herein synthesized branched LacNAc oligomers feature a variation of Lac(di)NAc epitopes and were confirmed to be potent inhibitors of human galectin-3 (Gal-3). The branched decasaccharide with two LacdiNAc-LacNAc branches ranks among the most potent poly-LacNAc-based Gal-3 inhibitors so far.

中文翻译：

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化学酶法合成支链N-乙酰半乳糖胺聚糖低聚物对Galectin-3的抑制作用

我们在这里提出了一个新的概念，用于分支的N-乙酰基乳糖胺（LacNAc）聚糖结构的合成。通过Leloir-糖基转移酶，半乳糖氧化酶和还原胺化的顺序酶促和化学反应的组合，我们获得了具有LacNAc和/或N'，N''变异的支链聚糖低聚物-二乙酰基乳糖胺（LacdiNAc）聚糖表位。分支点的引入通过优化的半乳糖氧化酶方案完成，使LacNAc低聚物的末端半乳糖具有C-6醛功能。通过糖基转移酶延长聚糖链后，将含C-6醛的线性结构单元与胺连接基官能化的聚糖偶联。发现甲醇和50℃的温度是α-甲基吡啶硼烷催化的还原胺化的最佳条件。在制备批次中，以高合成产率（约81％）获得了化学支链的聚糖。通过制备型HPLC分离产物，总收率良好（> 60％）。通过ESI-MS和NMR证明了结构的完整性。本文合成的支链LacNAc寡聚物的特征在于Lac（di）NAc表位的变异，并且被证实是人半乳凝素-3（Gal-3）的有效抑制剂。迄今为止，带有两个LacdiNAc-LacNAc分支的分支十糖属于最有力的基于poly-LacNAc的Gal-3抑制剂。