t-Boc-N-amido-PEG3-acid is a PEG linker containing a terminal carboxylic acid and Boc-protected amino group. The hydrophilic PEG spacer increases solubility 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. The Boc group can be deprotected under mild acidic conditions to form the free amine.
