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

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-diacetami do-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 cl eavage of carbohydrates split primarily 1,2-trans-beta-glycosidic linkages and did not affect amide-linked substituents. As a result, a disaccharide a nd a trisaccharide with a GlcNAc3NAcA residue at the reducing end were obta ined. Based on these data and studies of the initial polysaccharide and der ived oligosaccharides by two-dimensional NMR spectroscopy, the following st ructure of the tetrasaccharide repeating unit was established: --> 3)-alpha-D-QuipNAc4NAcyl-(1 --> 4)-beta-D-ManpNAc3NAcA6Ala-(1 --> 4)-be ta-D-GlcpNAc3NAcA-(1 --> 4)-beta-D-GlcpA-(1 -->.