Patent ID: 8143391

Claim:
A process for producing a water-soluble modified hyaluronic acid, which comprises converting a carboxy group contained in the glucuronic acid portion of hyaluronic acid or a salt thereof to a substituted amide group in a solvent consisting of dimethyl sulfoxide, using a condensing agent represented by the following formula (II): wherein each of R 10 , R 11 , R 12 , R 13 , R 14 , and R 15 is independently selected from a C 1-6 alkyl group, or each of R 10 and R 11 , R 12 and R 13 , and R 14 and R 15 may independently form a nitrogen-containing heterocycle together with a nitrogen atom to which they are attached; ring B represents a monocyclic or condensed ring nitrogen-containing heterocyclic group that may be substituted; and X − represents an anion; wherein the substituted amide group is formed by allowing hyaluronic acid or a salt thereof to react with one or more compounds selected from the group consisting of the following formulas: H 2 N—CH 2 —(CHR 5 ) m-2 —CH 2 —NH 2 ; H 2 N—CH 2 —CH 2 —(Y 4 —CH 2 —CH 2 ) t —NH 2 or; H 2 N—CH 2 —(CHR 6 ) p-2 —CH 2 —OH; wherein each of m and p independently represents an integer selected from 2 to 10; t represents an integer selected from 1 to 200; R 5 represents a hydrogen atom; R 6 represents a hydrogen atom or a hydroxyl group; and Y 4 represents an oxygen atom, wherein the modification ratio is from 60 mole % to 100 mole %; and wherein the modification ratio is defined as a ratio of total number of substituted amide groups relative to the total number of the carboxy groups originally contained in the hyaluronic acid or the salt thereof.