Fmoc-NH-PEGn-CH2COOH is a group of PEG linkers containing a Fmoc-protected amine and a terminal carboxylic acid, widely used in biochemistry and molecular biology research due to its exceptional reactivity and stability.  This series of compounds have been used to develop a variety of novel techniques and processes, including the synthesis of peptides, proteins, and other organic compounds, and also used in the synthesis of complex carbohydrates and for the modification of existing compounds. The hydrophilic PEG spacer increases solubility in aqueous media. The Fmoc group can be deprotected under basic conditions to obtain the free amine which can be used for further conjugations. 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.