Block co-oligomers of tri-O-methylated and unmodified cello-oligosaccharides as model compounds for methylcellulose and its dissolution/gelation behavior
Block co-oligomers of tri-O-methylated and unmodified cello-oligosaccharides as model compounds for methylcellulose and its dissolution/gelation behavior
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DOI：
10.1007/s10570-005-9003-6
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发表时间：
2006-08
期刊：
影响因子：
5.7
通讯作者：
Hiroshi Kamitakahara;F. Nakatsubo;D. Klemm
中科院分区：
文献类型：
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作者：
Hiroshi Kamitakahara;F. Nakatsubo;D. Klemm
设计了一种新的合成三-O-甲基化和未改性纤维低聚糖共聚低聚物的方法。这些低聚物是重要的模型化合物的商业甲基纤维素的溶解行为的调查。在这方面，洞察的化学结构的“交联位点”的甲基纤维素水溶液的热可逆凝胶化是特别重要的。合成过程包括使用糖基氟化物的糖基化和糖原酸酯的低聚。因此，作为糖基受体的苯基2，3，6-三-O-甲基-β-d-吡喃葡萄糖基-（1→4）-2，3，6-三-O-甲基-1-硫代-β-d-吡喃葡萄糖苷（1）被作为糖基供体的4-O-乙酰基-2，3，6-三-O-甲基-β-d-吡喃葡萄糖基-（1→4）-2，3，6-三-O-甲基-d-吡喃葡萄糖基氟化物（2）糖基化，转化为纤维四糖衍生物（3）。两种反应物均由市售纤维二糖制备。3，3-O-苄基-6-O-新戊酰基-α-d-吡喃葡萄糖（5）经脱乙酰基后，与纤维四糖衍生物（4）非还原端的4-羟基反应，得到嵌段共聚低聚物（6）。化合物6经脱保护后，得到三-O-甲基化-嵌段-未修饰的纤维寡糖（18和18 ′）（DP = 4 − 8，DS = 2.79 − 1.38），通过MALDI-TOF MS谱进行监测。 可溶于氯仿的甲基化纤维四糖衍生物（18和18 ′（DP=4，n=0），DS=2.57和2.79）也可溶于三-O-甲基化-嵌段-未修饰的纤维低聚糖（DP=4−8，DS=2.79−1.50）的水溶液中。这一事实表明，疏水甲基化的纤维四糖衍生物被封装在两亲性的三-O-甲基化-嵌段-未修饰的纤维寡糖的胶束内。结果表明，18和18 ′（DP=4−8，DS=2.79−1.38）在水和氯仿中的溶解度因DP和DS值的不同而有明显的差异。三-O-甲基化-嵌段-未修饰的纤维低聚糖的取代基沿着分子和分子间的分布对其在水和氯仿中的溶解度起重要作用。
A novel synthetic method for co-oligomers of tri-O-methylated and unmodified cello-oligosaccharides was designed. These oligomers are of importance as model compounds for investigations on the dissolution behavior of commercial methylcelluloses. In this connection, insights into the chemical structure of ‘cross linking loci’ in the thermo reversible gelation of aqueous solution of methylcellulose are of particular significance. The synthetic procedure consists of glycosylation using glycosyl fluoride and oligomerization of sugar orthoester. Thus, phenyl 2,3,6-tri-O-methyl-β-d-glucopyranosyl-(1→4)-2,3,6-tri-O-methyl-1-thio-β-d-glucopyranoside (1) as a glycosyl acceptor was glycosylated with 4-O-acetyl-2,3,6-tri-O-methyl-β-d-glucopyranosyl-(1→4)-2,3,6-tri-O-methyl-d-glucopyranosyl fluoride (2) as a glycosyl donor converted to give a cellotetraose derivative (3). Both reactants have been prepared from commercially available cellobiose. After deacetylation of3, 3-O-benzyl-6-O-pivaloyl-α-d-glucopyranose 1,2,4-orthopivalate (5) was reacted with 4-hydroxyl group at non-reducing-end of cellotetraose derivative (4) to give the block co-oligomer (6). After the deprotection of compound6, tri-O-methylated-block-unmodified cello-oligosaccharides (18and18′) (DP = 4 − 8, DS = 2.79 − 1.38) were obtained, monitored by MALDI-TOF MS spectra. Chloroform-soluble methylated cellotetraose derivatives (18and18′ (DP=4,n=0), DS=2.57, and 2.79, respectively) were also soluble in the water solution of tri-O-methylated-block-unmodified cello-oligosaccharides (DP=4−8, DS=2.79−1.50). This fact indicated that hydrophobic methylated cello-tetraose derivatives were encapsulated within a micelle of amphiphlic tri-O-methylated-block-unmodified cello-oligosaccharides. It was found that solubilities of18and18′ (DP=4−8, DS=2.79−1.38) in water and chloroform were obviously different in the mixtures, depending on their DP and DS values. The substituent distribution of the tri-O-methylated-block-unmodified cello-oligosaccharides along one molecule and between molecules plays an important role in its solubility in water and chloroform.