Resin is a common solid-phase carrier for solid-phase peptide synthesis (SPPS). Peptide is a kind of bio-active substance related to various cell functions in organisms. Its molecular structure is between amino acids and proteins. It is a compound composed of a variety of amino acids combined by peptide bonds in a certain order. The resin for peptide synthesis must have good physical properties, not only has certain mechanical strength, but also has stable chemical conditions in the synthesis process; The carrier must allow rapid and unimpeded contact between the growing peptide chain and the reagent; It is mainly necessary to contain connecting sites so that the peptide chain can be connected to these sites, and the peptide chain can be removed from the carrier after the connection is completed; In addition, the resin must provide enough connection points so that each unit volume of the resin can be connected to the peptide, and the interaction between the carrier and the peptide chain must be minimized.
There are three main types of resins used for the synthesis of peptides by solid-phase method: polystyrene styrene cross-linking resin, polyacrylamide, polyethylene glycol resin and derivatives. These resins can be directly connected to (the first) amino acids only by introducing reaction groups. According to the different reaction groups introduced, these resins and resin derivatives are divided into chloromethyl resin, carboxyl resin, amino resin or hydrazide resin. Chloromethyl resin is usually selected for t-butoxycarbonyl (BOC) synthesis method, such as Merrifield resin. Carboxyl resin such as Wang resin is usually selected for fluorene methoxycarbonyl (FMOC) synthesis.
The fixation of amino acids is mainly realized by the covalent bond formed between the carboxyl group of amino acids and the reaction group of the resin. There are many ways to form covalent bonds, such as chloromethyl resin. Generally, tetramethylammonium salt, sodium salt, potassium salt or cesium salt protecting amino acids are prepared first, and then react directly with resin at appropriate temperature or in appropriate organic solvents such as dioxane, dimethylfumarate (DMF) or dimethylsulfoxide (DMSO). For carboxyl resin, appropriate condensation agent such as dicyclohexylcarbodiimide (DCC) or carboxyl diimidazole is usually added to form a co-ester between the protected amino acid and the resin to complete the fixation of amino acid; Amino resin or hydrazide resin, after adding appropriate condensation agent such as DCC, completes the fixation of amino acids by protecting the amide bond formed between amino acids and the resin.