First application of triflic acid for selective cleavage of glycosidic linkages in structural studies of a bacterial polysaccharide from Pseudoalteromonas sp. KMM 634 †

Abstract

A marine bacterium Pseudoalteromonas sp. KMM 634 produces a highly acidic, regular O-specific polysaccharide, containing D-glucuronic acid (D-GlcA), 2,3-diacetamido-2,3-dideoxy-D-glucuronic acid (D-GlcNAc3NAcA), 2,3-diacetamido-2,3-dideoxy-D-mannuronoyl-L-alanine (D-ManNAc3NAcA6Ala) and 2-acetamido-2,4,6-trideoxy-4-[(S)-3-hydroxybutyramido]-D-glucose (D-QuiNAc4NAcyl). The polysaccharide was stable towards solvolysis with anhydrous HF but could be partially depolymerised by triflic acid. This new reagent for selective cleavage of carbohydrates split primarily 1,2-trans-β-glycosidic linkages and did not affect amide-linked substituents. As a result, a disaccharide and a trisaccharide with a GlcNAc3NAcA residue at the reducing end were obtained. Based on these data and studies of the initial polysaccharide and derived oligosaccharides by two-dimensional NMR spectroscopy, the following structure of the tetrasaccharide repeating unit was established: