Chitosan derivatives and methods for preparing the same

A method for the preparation of a compound of Formula (I)

• wherein
• n is an integer greater than or equal to 3,
• W is N-acetyl:
• in from 0 to 70 molar % of monomer units,
• and when it is not N-acetyl it is a group selected from:
• wherein each R1 substituent may be the same or different and is independently selected from H, CH3, and —(CH2)a—CH3, wherein a is from 1 to 11, or
• when W is not N-acetyl it is a group selected from:
• wherein each R1 substituent is independently selected from H, CH3, and —(CH2)a—CH3, wherein a is from 1 to 11, and wherein R2 is selected from:
• wherein i is an integer from 1-200, preferably 1-50, more preferably 1-10, and R3 is selected from H, —(CH2)j—CH3 and —CO—(CH2)j—CH3, wherein j is 0, 1, 2, 3, 4 or 5;
• and
• wherein R is H in at least 75 molar % of the total number of positions, and when it is not H, R is the same as either amino substituent R1 or R2 on substituent W;
• or a salt thereof,
• the method comprising steps of
• (a) dissolving a chitosan compound with formula
• wherein n is an integer greater than or equal to 3, wherein R is H, and wherein W is —NH2 or N-acetyl,
• or a salt thereof, in a solution that contains at least 1 equivalent of an acid for each equivalent of —NH2 in the chitosan compound;
• (b) adding at least one alkylation agent to the solution from step (a), selected from:
• (i) alkyl halides, dialkyl sulfates, dialkyl, alkyl methanosulfonates, carbonates, and alkyl-p-toluenesulfonates, with structure:
• wherein each S1 substituent is independently selected from CH3, and —(CH2)a—CH3, wherein a is from 1 to 11, or wherein S1 is selected from:
• wherein i is an integer from 1-200, preferably 1-50, more preferably 1-10, and S2 is selected from H, —(CH2)j—CH3 and —CO—(CH2)j—CH3, wherein j is 0, 1, 2, 3, 4 or 5, and (ii) alkyl epoxides selected from:
• and at least one base in an amount that is at least sufficient to neutralize the acid of step (a).