DBCO-PEG12-acid is an analog of DBCO-Acid with hydrophilic PEG linker and a DBCO group. The DBCO groups is commonly used for Click Chemistry reactions. The hydrophilic PEG chain allows for increased water solubility of compounds in aqueous media. The terminal carboxylic acid can react with primary amine groups in the presence of activators (e.g. EDC, or HATU) to form a stable amide bond.