Purification of substituted diaminopyrazine dicarboxylic acids

A method for purifying a compound of Formula (I) or salt thereof from the precipitated reaction product comprising the compound of Formula (I), impurities, and/or residual or entrained solvents,

• the method comprising:
• (a) contacting the precipitated reaction product comprising the compound of Formula (I), impurities, and/or residual or entrained solvents with a solvent forming a first reaction mixture;
• (b) performing at least one distillation of the first reaction mixture under vacuum maintaining a temperature below 40° C. forming a second reaction mixture;
• and
• (c) cooling the second reaction mixture to a temperature of about 0° C.;
• and
• (d) isolating the compound of Formula (I) from the second reaction mixture;
• wherein the ester portion of the ester amino acid (AA ester) is an C1-C10 unsubstituted alkyl or a C1-C10 substituted alkyl.