A polysaccharide derivative that consists of a backbone of alpha-D-glucosyl-(1->4)-5,7-diacetyl-alpha-D-neuraminosyl repeating units, joined together by glycosidic linkages between position 2 of the diacetylneuraminosyl residues and position 6 of the glucosyl residues. The depicted structure is representative and shows the repeating unit, which is variably O-acylated at the 7-position of the neuraminosyl residues.