Selective Hydrolysis of the 3,6-Anhydrogalacotosidic Linkage in Red Algal Galactan: A Combination of Reductive Acid Hydrolysis and Anhydrous Mercaptolysis
作者:Yoichiro HAMA、Aya TSUNEOKA、Ryoji MORITA、Osamu NOMOTO、Kenshi YOSHINAGA、Hideo HATATE、Toshihisa SUMI、Hiroki NAKAGAWA
DOI:10.1271/bbb.100306
日期:2010.9.23
Here we report a simple method for the structural analysis of red algal galactan containing 3,6-anhydrogalactose. Structural heterogeneity in the galactan was demonstrated by this method. For selective hydrolysis of 3,6-anhydrogalactosidic linkages in the galactan, conditions for reductive mild acid hydrolysis were examined by characterizing the resulting oligosaccharide alditols by anhydrous mercaptolysis. Residues other than alditols at the reducing ends, including labile 3,6-anhydrogalactose, were liberated quantitatively as diethyl dithioacetal derivatives, whereas alditols at the reducing ends were not derivatized and were liberated as alditols intact. The liberated sugars were then separated and measured quantitatively by gas-liquid chromatography. Heating of agarose in reductive hydrolysis with 0.3 m trifluoroacetic acid in the presence of an acid-stable reducing agent, 4-methyl morpholine borane, at 80 °C for 90 min and for 90 °C for 45 min was found to be optimum for the selective hydrolysis of 3,6-anhydrogalactosidic bonds, without detectable cleavage of other glycosidic bonds.
在此,我们报告了一种对含有3,6-脱水半乳糖的红藻半乳聚糖进行结构分析的简单方法。该方法证明了半乳聚糖的结构异质性。为了选择性地水解半乳聚糖中的3,6-脱水半乳糖苷键,通过无水硫醇化法表征所得低聚糖醛糖醇,研究了温和酸性水解的条件。还原末端除醛糖醇以外的残留物,包括不稳定的3,6-脱水半乳糖,被定量地释放为二乙基二硫代缩醛衍生物,而还原末端的醛糖醇则不被衍生化,并作为完整的醛糖醇释放。然后通过气相色谱法分离并定量测量释放的糖。在酸性稳定的还原剂4-甲基吗啉硼烷的存在下,用0.3 m三氟乙酸在80 °C加热琼脂糖90分钟,然后在90 °C加热45分钟,这是选择性地水解3,6-脱水半乳糖苷键的最佳条件,且不会检测到其他糖苷键的断裂。