title: Mechanism of mild acid hydrolysis of galactan polysaccharides with highly ordered disaccharide repeats leading to a complete series of exclusively odd-numbered oligosaccharides.
abstract: Sulfated galactan kappa-carrageenan is a linear polysaccharide with a repeating disaccharide sequence of alternating 4-sulfated 3-linked galactose and 4-linked 3,6-anhydrogalactose units. In contrast to many examples of chemical hydrolysis of polysaccharides, mild acid treatment of kappa-carrageenan resulted in facile and highly specific cleavage. In this article, we report the identification, by various MS and chromatographic techniques, of an unexpected series of exclusively odd-numbered oligosaccharide fragments from its hydrolytic products. Detailed sequence analysis of the products indicated that all the oligosaccharide fragments have the 4-sulfated 3-linked galactose residues at both the reducing and the nonreducing ends. Further detailed investigation and analysis suggested that these odd-numbered oligosaccharides were derived from two-step cleavages of the glycosidic bonds on either sides of the 3,6-anhydrogalactose residues. Neutral galactan agarose also contains 3,6-anhydrogalactose and has a similar backbone sequence, and exhibited similar results upon mild acid hydrolysis. It is highly unusual to obtain exclusively odd-numbered oligosaccharides from polysaccharides composed of ordered disaccharide repeats.
authors.affiliation: Glycoscience and Glycoengineering Laboratory, School of Medicine and Pharmacy, Ocean University of China, Qingdao, China.
authors.forename: Bo
authors.initials: B
authors.lastname: Yang
authors.forename: Guangli
authors.initials: G
authors.lastname: Yu
authors.forename: Xia
authors.initials: X
authors.lastname: Zhao
authors.forename: Guangling
authors.initials: G
authors.lastname: Jiao
authors.forename: Sumei
authors.initials: S
authors.lastname: Ren
authors.forename: Wengang
authors.initials: W
authors.lastname: Chai
mesh_terms: D002240:Carbohydrate Sequence; D002351:Carrageenan / Q000737:chemistry; D004187:Disaccharides / Q000737:chemistry; D005685:Galactans / Q000737:chemistry*; D006868:Hydrolysis; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000032:analysis / Q000737:chemistry*; D011134:Polysaccharides / Q000737:chemistry*; D013431:Sulfates / Q000737:chemistry; D053719:Tandem Mass Spectrometry
chemical_list: D004187:Disaccharides; D005685:Galactans; D009844:Oligosaccharides; D011134:Polysaccharides; D013431:Sulfates; D002351:Carrageenan