Fmoc-NH-PEG12-COOH, also known as Fmoc-N-amido-PEG12-acid, is a PEG derivative containing a protected form of propionic acid modified with Fmoc (9-FLUORENYLME- THOXYCARBONYL) and PEG12 (polyethylene glycol 12). It is useful in the synthesis of peptides and biomolecules. For example, it can be used to tether peptides to proteins or other large biomolecules (e.g. nucleic acids). The attachment of hydrophobic peptides, NH2-PEG12, can effectively reduce aggregation. Also, it can act as a linker for Antibody-Drug Conjugates (ADCs)