Precise Chemical Synthesis of Physiologically Active Branched Polysaccharides

本研究的目的是通过1,3-无水糖衍生物的开环聚合，合成在其6位具有β -d -葡萄糖分支的明确分支的(1-3)- β -d -葡聚糖。目标多糖的合成采用两种不同的方法：1)聚合1,3-无水- β - d -葡萄糖衍生物(1)，然后对所得聚合物的对甲氧基苯基进行选择性脱保护，随后在6位进行立体特异性糖苷化，最后对产物进行完全脱保护。2)聚合1,3-无水- β - d -葡萄糖衍生物(2)，在其6位上含有β - d -葡萄糖片段，然后对所得聚合物进行脱保护。从纤维素开始，经过9个步骤的反应，合成了1。然而，在氯化氢对二乙酸(3)的氯化过程中，甲氧基苯基被去除。因此，有必要寻找更合适的保护群体和更温和的反应条件。以纤维素为原料，经过11步反应，合成了2。在最后的分子间双环化步骤中，前体氯化物(4)的脱氢氯化反应主要发生，产生葡萄糖衍生物作为主要产物。单体2的收率为14%。因此，必须优化反应条件以提高所需产物的产率2。以1,3-无水-2,4,6-三- o-苄基- - d -葡萄糖吡喃糖为研究对象，研究了改性有机铝催化剂对1,3-无水糖衍生物立体定向聚合的影响因素。

The objective of this study is to synthesize well-defined branched(1-3)-beta-D-glucans having beta-D-glucoss branches at their 6-positions via ring-opening polymerization of 1,3-anhydro sugar derivatives. Synthesis of the target polysaccharides was undertaken by two different approaches : 1)Polymerization of 1,3-anhydro-beta-D-glucose derivative (1), followed by selective deprotection of the p-methoxybenzyl group of the resulting polymer, subsequent stereospecific glycosidation at the 6-position, and finally complete deprotection of the product, and 2) polymerization of 1,3-anhydro-beta-D-glucose derivative (2) bearing a beta-D-glucose moiety in its 6-position, followed by deprotection of the resulting polymer.The synthesis of 1 was attempted via a 9 steps reaction sequence starting from cellulose. However, the methoxybenzyl group was removed during the chlorination of the diacetate (3) by hydrogen chloride. Therefore it is necessary to look for a more appropriate protecting group as well as milder reaction conditions. The synthesis of 2 was also undertaken with cellulose as a starting material through an 11 step reaction sequence. In the final intermolecular bicyclization step, the dehydrochlorination of the precursor chloride (4) predominantly occurred to yield a glucal derivative as the major product. The monomer 2 was cbtained in a yield of 14%. Therefor, the reaction conditions must be optimized to improve the yield of the desired product 2.Polymerization of 1,3-anhydro-2,4,6-tri-O-benzyl-beta-D-glucopyranose was investigated in order to clarify the factors influencing the stereospecific polymerization of 1,3-anhydro sugar derivatives by modified organoaluminum catalysts.