A cleavage cocktail for methionine-containing peptides

Area of Science:

• Peptide Chemistry
• Organic Synthesis
• Biochemistry

Background:

• 9-fluorenylmethoxycarbonyl (Fmoc)-based solid-phase peptide synthesis is a common method for peptide production.
• Methionine residues in peptides are susceptible to oxidation during cleavage and deprotection.
• Minimizing side-chain oxidation is crucial for obtaining pure and active peptides.

Purpose of the Study:

• To develop a novel cleavage and deprotection cocktail for Fmoc-based peptide synthesis.
• To minimize methionine side-chain oxidation during peptide synthesis.
• To evaluate the efficacy of the new cocktail, Reagent H, in synthesizing methionine-containing peptides.

Main Methods:

• A new cocktail, Reagent H (trifluoroacetic acid, phenol, thioanisole, 1,2-ethanedithiol, water, dimethylsulphide, ammonium iodide), was formulated.
• Reagent H was used for cleavage and deprotection of a model pentadecapeptide and a 28-amino acid peptide from DsbC.
• The synthesized peptides were analyzed for methionine sulphoxide formation and yield using various cleavage cocktails.

Main Results:

• Reagent H prevented methionine sulphoxide formation in synthesized peptides, unlike conventional cocktails (K, R, B).
• Addition of ammonium iodide to conventional cocktails reduced methionine sulphoxide but also decreased peptide yield.
• Reagent H produced the reduced dithiol form of a 28-amino acid peptide in 51% yield and the intramolecular disulphide form in 35% yield.

Conclusions:

• Reagent H is a highly effective cocktail for cleavage and deprotection in Fmoc-based peptide synthesis, particularly for methionine-containing peptides.
• The new cocktail minimizes methionine side-chain oxidation, leading to higher purity crude peptides.
• Reagent H facilitates the controlled formation of specific peptide disulfide bond structures.