tailieunhanh - Báo cáo khoa học: Mechanism of mild acid hydrolysis of galactan polysaccharides with highly ordered disaccharide repeats leading to a complete series of exclusively odd-numbered oligosaccharides

Sulfated galactanj-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 j-carra-geenan resulted in facile and highly specific cleavage. | Mechanism of mild acid hydrolysis of galactan polysaccharides with highly ordered disaccharide repeats leading to a complete series of exclusively odd-numbered oligosaccharides Bo Yang1 Guangli Yu1 Xia Zhao1 Guangling Jiao1 Sumei Ren1 and Wengang Chai1 2 1 Glycoscience and Glycoengineering Laboratory Schoolof Medicine and Pharmacy Ocean University of China Qingdao China 2 Glycosciences Laboratory Faculty of Medicine ImperialCollege London Harrow UK Keywords acid hydrolysis agarose carrageenan mass spectrometry polysaccharide Correspondence W. Chai Glycosciences Laboratory Faculty of Medicine ImperialCollege London Northwick Park St Mark s Campus Harrow Middlesex HA1 3UJ UK Fax 44 20 8869 3455 Tel 44 20 8869 3255 E-mail G. Yu Glycoscience and Glycoengineering Laboratory Schoolof Medicine and Pharmacy Ocean University of China Qingdao 266003 China Fax 86 532 8203 3054 Tel 86 532 8203 1560 E-mail glyu@ Received 6 November 2008 revised 30 December 2008 accepted 4 February 2009 Sulfated galactan K-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 K-carra-geenan 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 .