Mechanism of mild acid hydrolysis of galactan polysaccharides with highly ordered disaccharide repeats leading to a complete series of exclusively odd‐numbered oligosaccharides

Abstract

The diverse oligosaccharide sequences present in poly-saccharides, glycoproteins, glycolipids and proteogly-cans serve multiple functions. Acidic polysaccharide glycosaminoglycans (GAGs) are ubiquitous in vertebrate tissues, and have important biological functions through binding to various proteins. Marine-derived polysaccharides are often of an anionic nature, and these GAG-like molecules have been exploited for their antiviral, antioxidant, anticoagulant and other signal-ing activities [1-4]. Recent studies have shown that marine polysaccharide carrageenans can inhibit the attachment of several pathogenic viruses, e.g. herpes simplex virus [5], dengus virus [6], and human papillo-mavirus [7,8], and hence they have become of considerable biomedical interest, owing to their antiviral activities and therapeutic potential. Carrageenans are highly sulfated galactans isolated from marine red algae, with linear repeating sequences Sulfated galactan j-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. 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 oligo-saccharides from polysaccharides composed of ordered disaccharide repeats. Abbreviations A, 4-linked a-3,6-anhydrogalactose; A2S, 4-linked 2-O-sulfated-aD -3,6

Production of agaro- and carra-oligosaccharides by partial acid hydrolysis of galactans

“…However, due to the instability of 3,6-anhydro-galactose units to harsh acidic conditions, partial hydrolysis with strong and concentrated acids can also produce the reducing trisaccharide 3 containing galactose as the terminal unit (Yang et al, 2009). A good alternative for preserving the anhydro units is the addition of reducing (Usov & Elashvili, 1991;Gonçalves et al, 2002) or oxidizing (Penman & Rees, 1973) agents during the hydrolysis step to produce alditol or aldonic oligosaccharides, respectively.…”

A Novel Agarolytic β-Galactosidase Acts on Agarooligosaccharides for Complete Hydrolysis of Agarose into Monomers

“…Acid hydrolysis using a strong acid at a high temperature is a simple, less expensive, and rapid method (5,6); however, this method produces sugar degradation products such as 5-hydroxymethylfurfural (6)(7)(8)(9), which can inhibit fermentative microorganisms (10,11). This problem is circumvented by the enzymatic hydrolysis method because it is performed at a milder temperature.…”

Selective Hydrolysis of the 3,6-Anhydrogalacotosidic Linkage in Red Algal Galactan: A Combination of Reductive Acid Hydrolysis and Anhydrous Mercaptolysis

“…These results appear to have resulted from the destruction of AG at the reducing end, as observed for meethod II. The latter researchers, 19) however, reported the exclusive formation of oddnumbered oligosaccharide alditols obtained by reductive hydrolysis in the presence of MMB.…”

“…15) Similar results, including the formation of even-numbered oligosaccharides from red algal galactans, have been reported by several other researchers. 16,17) On the other hand, Yu 18) and Yang et al 19) reported recently the formation of odd-numbered oligosaccharides by mild acid hydrolysis of -carrageenan and both -carrageenan and agarose, respectively. In their studies, residues at the reducing end were determined to be Gal, not AG.…”