||The N-hydroxysuccinimide (NHS) active ester of polyethylene glycol carboxylic acid can react with the amine group of lysine. The coupling reaction only requires a short reaction time under mild reaction conditions, pH 7-9, low temperature (5-25°C). A physiologically stable amide bond is formed.
||The primary amine is converted to a secondary amine by reductive amination in the presence of a reducing agent such as sodium borohydride or sodium cyanoborohydride. The pH is important for reductive amination. PEG-Aldehyde is a very good reagent for N-terminal PEGylation grafting.
||It reacts with amine to form stable thiourea.
||Usually the acid needs to be activated, such as an NHS ester.
||Under suitable conditions, the amine can be reacted with NPC functionalized PEG.
||The Michael addition reaction of amines and acrylates is a relatively slow reaction.