夹竹桃叶中一种阿拉伯半乳葡聚糖的化学结构

夹竹桃叶用 ３％ Ｎａ_２ＣＯ_３溶液提取，经ＤＥＡＥ－Ｓｅｐｈａｄｅｘ Ａ－２５阴离子交换层析，ＳｅｐｈａｄｅｘＧ－２００凝胶过滤法分离纯化，得到一种中性异多糖 ＮＩＢ－１，分子量为４ ３００，［ａ］_Ｄ~（２０）＋１１４． ７（ｃ，０．２，Ｈ_２Ｏ），由Ｌ－Ａｒａ，Ｄ－Ｇａｌ和Ｄ－Ｇｌｃ构成。用化学分析及ＮＭＲ方法研究了其化学结构，由１，４连接的ａ－Ｄ－葡萄糖残基构成主链，阿拉伯糖和半乳糖分布于支链上，有多种分支形式，分支点在葡萄糖残基的６－Ｏ上。

Chemical Strucure of an Arabinogalactoglucan from Sweet-scented Oleander Leaves (Nerium indicum)

From the fresh leaves of Nerium indicum Mill., a neutral polysaccharide NIB--1 was isolated by extraction with 3% aqueous sodium carbonate, and with fractionation using DEAE--Sephadex A--25 and Sephadex G--200 chromatography. NIB--1 was shown to be homogeneous by HPGPC, and had a molecular weight of 4 300, and a ]_D~(20) 114. 7 (c, 0. 2, H_2O). It was composed of L-arabinose, D--galactose and D- glucose, in the molar ratios of 1: 6: 10. Its main structural features were elucidated by methylation analysis, periodate oxidation, partial acid hydrolysis and ~1H and ~(13)CNMR spectroscopy. The data available indicated that NIB--1 has a backbone consisting of a (1-4) linked glucosyl residues, with branches at the O-6, composed of arabinosyl and galactosyl residues.