Synthesis of Branched Polysaccharides Having Hypoglycaemic Activity

以2，4-二-O-苄基-(1*6)-α-D-葡聚糖为原料，通过阳离子开环聚合，在C-3位上进行木糖缩合反应，得到木吡喃葡聚糖衍生物。木糖基三氯乙酰亚氨酸酯作为糖基化试剂时，木糖化反应的立体选择性较低。为了改善天然多糖的物理性质，在(1*3)-β-D-吡喃葡聚糖中引入了葡萄糖支链。Curdlan通过C-6位的区域选择性三甲基化，然后C-2和C-4位的苯氨基甲酰化来保护。选择性地脱保护(脱三聚)的柯德兰经葡糖基化得到含葡糖基支链的(1*3)-β-D-葡聚糖衍生物。还尝试了对得到的支链多糖进行去保护。对天然多糖柯德兰进行了二甲氧基三甲基化、苯氨基甲酰化和去甲氧基三苯甲化反应，制备了一种区域选择性保护的多糖。然后用葡萄糖吡喃糖基三氯乙酰亚氨酸酯对区域选择性保护的柯德兰进行糖基化。

2,4-Di-O-benzyl- (1*6) -alpha-D-glucopyranan which was prepared by cationic ring-opening polymerization of an anhydro glucose derivative was xylosylated at the C-3 position to give xylopyranosyl glucopyranan derivatives. Stereoselectivity of the xylosylation with xylopyranosyl trichloroacetimidate as glycosylating reagent was low. Glucosyl branches were introduced into curdlan ((1*3)-beta-D-glucopyranan) for the purpose of improvement of physical properties of natural polysaccharides. Curdlan was protected by regioselective tritylation at C-6 position, followed by phenylcarbamoylation at C-2 and C-4. Selectively deprotected (detritylated) curdlan was glucosylated to give (1*3) -beta-D-glucopyranan derivative with glucopyranosyl branches. Deprotections of the obtained branched polysaccharide were also attempted. Natural polysaccharide curdlan was then dimethoxytritylated, phenylcarbamoylated, and dedimethoxytritylated in order to prepare a regioselectively protected polysaccharide. The regioselectively protected curdlan was subsequently glucosylated with glucopyranosyl trichloroacetimidate.