Ac-S-OEG-OH is a modified L-serine derivative used as a building block in peptide synthesis. The N-acetyl group protects the amino terminus, while the oligoethylene glycol (OEG) chain attached to the serine side chain hydroxyl enhances hydrophilicity, improving water solubility and flexibility in peptide structures. This facilitates easier handling, purification, and biocompatibility in applications such as pharmaceutical development, bioactive peptide assembly, and biomaterial surface modifications. It serves as a linker to optimize interactions with target molecules in biochemical research and drug delivery systems.