The Fluorene methoxy carbonyl (Fmoc) group is an alkali-sensitive protective group, which can be removed in concentrated ammonia or dioxane-methanol/4M NaOH solution and 50% dichloromethane solution of piperidine, ethanolamine, cyclohexylamine, 1,4-dioxane, pyridinone. Under weak alkali conditions such as sodium carbonate or sodium bicarbonate, Fmoc-Cl or Fmoc-OSu is generally used to introduce the Fmoc protecting group. Compared with Fmoc-Cl, Fmoc-OSu is easier to control the reaction conditions and has fewer side reactions. The Fmoc protecting group is particularly stable under acidic conditions, but is very sensitive to alkaline conditions. Thus, it is usually used together with acid-sensitive protecting groups BOC or CBZ to protect amino acids containing active side chain groups. Fmoc has strong ultraviolet absorption, which can be detected by ultraviolet absorption and brings many conveniences to automatic peptide synthesis of the instrument. And Fmoc is compatible with a wide range of solvents and reagents and used in a variety of supports and activation methods as well as has high mechanical stability. Therefore, Fomc-amino acids are the most commonly used in peptide synthesis today.
The general Fmoc-protected amino acids synthesis step is to add the amino acids to a mixed solution of water and sodium bicarbonate with stirring and cool the resulting solution to 5 °C, then slowly add Fmoc-OSu or Fmoc-Cl. After the resulting mixture is kept at 0 °C for 1 hour, and then heat to room temperature for one night. Then water is added and the aqueous layer is extracted twice with EtOAc. The organic layer is back extracted with saturated sodium bicarbonate solution twice. The combined aqueous layer is acidified to pH 1 with 10% hydrochloric acid and then extracted with EtOAc for 3 times. The combined organic layers are dried (sodium sulfate) and concentrated in vacuo and the resulting residue could be purified by flash chromatography (SiO).
Anti-corrosion: Fmoc-amino acids play an important role in solid-phase peptide synthesis. For example, Fmoc-glycine is Fmoc-protected glycine, which is mainly used to synthesize peptides. The difference of amino acids protecting groups have a great influence on the efficiency and yield of peptide synthesis. Fmoc-glycine can be used to prepare a glycine derivative corrosion inhibitor. Through the amidation reaction, Fmoc-protecting groups and hydrophobic long chains are connected to the glycine molecule through heteroatoms (N, O or unsaturated bonds). It can adsorb on the metal with the biphenyl ring containing π electrons, and the hydrophobic long chain blocks water molecules, so that it forms a protective film on the steel surface to achieve the purpose of anticorrosion.
Therapeutic and antibacterial: Some studies have found that several Fmoc-amino acids have extensive anti-inflammatory activity. In vitro studies, Fmoc-modified amino acids blocked the recruitment of neutrophils to the site of inflammatory injury and inhibited T cell activation instead of traditionally inhibiting lipid metabolism enzymes or increasing circulating levels of endogenous glucocorticoids. Therefore Fmoc-amino acid may be a valuable therapeutic agent for inflammatory diseases
Biocatalysis: Fmoc-amino acid modified molecular assembly has the characteristics of fast assembly, outstanding stability and easy modification, so it has effective catalytic performance.
Drug delivery: Fmoc has strong hydrophobicity and the ease of peptide sequence modification. The Fmoc-amino acids modified assembly can play a dual role of encapsulation and functionalization in the drug delivery of organisms.