The succinimidyl valerate is an active ester used for the PEGylation of primary amines. The reaction of the SVA with an amine forms a stable amide linkage. This reaction may be performed in an organic solution with a base catalyst or may be performed in an aqueous solution at a pH range of 8 to 9. The reaction should be allowed to mix for a minimum of 4 hours. By tailoring the pH of a reaction, the selectivity for the PEGylation of a specific site is increased.