L-Isoleucine is an essential, branched-chain amino acid (BCAA) with the molecular formula C6H13NO2. It is one of the 20 standard proteinogenic amino acids and exists as a single stereoisomer (L-form). It is characterized by a β-branched side chain, making it hydrophobic and contributing to its unique structural and metabolic roles. Its primary applications are in the pharmaceutical and nutritional sectors. In medicine, it is a critical component of parenteral nutrition formulations and amino acid infusion solutions, used to correct nitrogen balance and support protein synthesis in patients. It is also a key ingredient in dietary supplements and sports nutrition products aimed at muscle recovery and growth, due to its role in muscle protein metabolism. Furthermore, L-isoleucine serves as a chiral building block in the synthesis of peptides and other bioactive compounds. As a fundamental biochemical, it is also widely used in cell culture media, microbiological research, and as a standard in analytical chemistry. While it has specific biological functions, its structure also qualifies it as a versatile chiral amine synthon in organic synthesis, particularly for introducing the isoleucine moiety or its derivatives into more complex molecules.