This bifunctional reagent, featuring a free carboxylic acid and an N-hydroxysuccinimide (NHS) ester separated by a flexible octanoate chain, is used in bioconjugation and peptide synthesis. The NHS ester enables selective and efficient reaction with primary amines to form stable amide bonds under mild, aqueous conditions, while the pendant carboxylic acid can be subsequently activated for further coupling. It minimizes racemization and side reactions, making it ideal for constructing pharmaceutical intermediates, bioconjugates, and complex peptides. Applications include protein modification, targeted drug delivery systems, diagnostic agent development, and functionalization of polymers.