Amino acids are amphoteric organic compounds containing both a basic amino group and an acidic carboxyl group. While more than 500 amino acids occur in nature, the 22 α-amino acids used to build proteins are the most biologically significant. Protected amino acids are primarily classified into three categories: α-Amino protection, α-Carboxyl protection, Side-chain reactive group protection. These protected amino acids are essential for the synthesis of peptide and protein drugs. They maintain the integrity and stability of amino acids during synthesis, thereby enhancing the drug's stability and bioactivity.

Peptide fragments are short chains of amino acids with or without protecting functional groups, typically consisting of 2-20 amino acids. As crucial intermediates in the synthesis of peptide and protein drugs, peptide fragments enable efficient construction of structurally complex therapeutic peptides and protein drugs through solid-phase or liquid-phase synthesis strategies. Drug development based on fragment peptides has been widely applied in various biomedical fields, including antitumor therapies, anti-infective treatments, metabolic disease management, and vaccine research.

Side chain modification is one of the key technologies for optimizing peptide and protein drugs. Common sidechain types include polyethylene glycol (PEG) chains, fatty acid chains, and carbohydrate chains. The sidechain modification can increase molecular weight to reduce renal clearance and prolong drug half-life, while creating steric hindrance to resist enzymatic degradation and enhance drug stability. The side chain modification technology provides an important approach for developing peptide and protein drugs, demonstrating broad prospects in therapeutic areas such as cancer, diabetes, and cardiovascular diseases.