Method of preparation of an oxidized derivative of hyaluronic acid and a method of modification thereof

A method of modification of a hyaluronic acid derivative comprising:

• reacting hyaluronic acid with 4-R-TEMPO and a co-oxidant in a protic solvent, where R is a linear or branched alkyl chain, optionally containing aromatic or heteroaromatic groups, wherein the oxidized derivative of hyaluronic acid is selectively oxidized to an aldehyde at position 6 of the glucosamine portion of the derivative and 4-R-TEMPO is present in an amount within the range from 0.005 to 0.5 molar equivalent with respect to the hyaluronic acid;
• and
• reacting the oxidized hyaluronic acid derivative with either a compound of a general formula H2N-R, where the general formula H2N-R defines an amino acid, peptide, or polysaccharide containing a free amino group or where R is a linear or branched C1—C30 alkyl chain, optionally containing aromatic or heteroaromatic groups, thereby defining an amine, or with a hyaluronan, substituted by an -R-NH2 group, where R is a linear or branched C1—C30 alkyl chain, optionally containing aromatic or heteroaromatic groups, to form an imino form of HA of a general formula I