Isolation, modification, and NMR assignments of a series of cellulose oligomers
Isolation, modification, and NMR assignments of a series of cellulose oligomers
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DOI：
10.1021/ja990561u
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发表时间：
1999-08-11
影响因子：
15
通讯作者：
Petillo, PA
中科院分区：
文献类型：
--
作者：
Flugge, LA;Blank, JT;Petillo, PA
已从微晶纤维素的水解产物中分离出一系列来自2至8个重复亚基的纤维素低聚物，并对其进行了尺寸分级。将纤维三糖（1）、纤维四糖（2）、纤维五糖（3）和纤维六糖（4）化学修饰为相应的β-甲基糖苷13-16分三步进行，总产率为16- 46%。全乙酰化以70-75%产率产生寡聚物5-8，随后形成β-甲基糖苷以42-89%产率产生9-12。用胍除去乙酸酯保护基得到13-16，产率为73-79%。这种修改消除了异头平衡，并允许详细的NMR溶液研究这些低聚物。通过DQF-COSY、HMQC、HMBC和HMQC-TOCSY实验的组合获得每个全乙酰化和去保护的低聚物的完整H-1和C-13化学位移归属。甲基纤维三糖（13）和甲基纤维四糖（14）中的所有共振都容易彼此区分并可直接归属。观察到甲基纤维五糖（15）和甲基纤维六糖（16）的内部吡喃糖环的共振的严重重叠，并且只能使用3D脉冲序列的综合电池来解析和分配。这些结果表明，多维NMR实验的效用分配的信号从一个重复的多糖和代表的第一个必要的步骤，在一个全面的，系统的研究纤维素低聚物在溶液中。
A homologous series of cellulose oligomers from two to eight repeating subunits have been isolated and size-fractionated from the hydrolysis products of microcrystalline cellulose. Chemical modification of cellotriose (1), cellotetraose (2), cellopentaose (3), and cellohexaose (4) to the corresponding beta-methyl glycosides 13-16 proceeded in three steps in overall yields of 16-46%. Peracetylation produced oligomers 5-8 in 70-75% yield, and subsequent formation of the P-methyl glycosides gave 9-12 in 42-89% yield. Removal of the acetate-protecting groups employing guanidine provided 13-16 in 73-79% yield. This modification eliminated anomeric equilibration and permitted a detailed NMR solution study of these oligomers. The complete H-1 and C-13 chemical shift assignments of each peracetylated and deprotected oligomer were obtained through a combination of DQF-COSY, HMQC, HMBC, and HMQC-TOCSY experiments. All the resonances in methyl cellotriose (13) and methyl cellotetraose (14) were readily distinguishable from one another and directly assignable. Severe overlap of the resonances for the inner pyranose rings of methyl cellopentaose (15) and methyl cellohexaose (16) was observed and could only be resolved and assigned using a comprehensive battery of 3D pulse sequences. These results demonstrate the utility of multidimensional NMR experiments in assigning the signals from a repeating polysaccharide and represent the first necessary step in a comprehensive, systematic study of cellulose oligomers in solution.