Hyalobiuronic acid, a glucuronido glucosamine earlier isolated from hydrolysates of hyaluronic acid from umbilical cord, has been converted to its heptaacetyl methyl ester and its N-acetyl derivative. Esterification of the disaccharide, oxidation of the glucosamine residue to glucosaminic acid, and reduction of the uronic ester residue to a glucose residue yields a crystalline glucosidoglucosaminic acid. This is oxidatively deaminated to give a glucosidoarabinose, isolated as its crystalline heptaacetate, identical with the heptaacetate VI1 obtained by Zernplen degradation of laminaribiose (VIII). Hyalobiuronic acid is thus 3-O-(~-~-glucopyranosyluronic acid)-2-amino-2-deoxy-D-g~ucose (I). That its N-acetyl derivative I1 is the basic repeating unit of hyaluronic acid linked linearly in the polymer, probably by 3-0-(2-acetamido-2-deoxy-j3-~-g~ucopyranosyl) linkages (Fig. 2 ) , follows from earlier hydrolytic and enzymatic experiments, and from periodate oxidation data in the literature. A modification of the hydroxamic acid test suitable for sugar esters is described. (24) We are indebted to Prof. E. L. Hirst for seed material. (25) W. E. Trevelyan and J. S. Harrison, Biochcm. J . , 60, 298 (1 952). (26) W. hlcjhnrini. Z . p h y s i o l . Chmi., '268, 117 (193!)).
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