Cleavage Cocktail for Peptides Containing Cys, Met, Trp and Tyr Residues (Reagent K)1

Cleavage Cocktail for Peptides Containing Cys, Met, Trp and Tyr Residues (Reagent K)

This cleavage cocktail is commonly used to cleave peptides containing combinations of sensitive residues such as cysteine, methionine, tryptophan and tyrosine. Since this reagent is suitable to most of the sensitive amino acid residues, it is often used as a general cleavage reagent. This reagent is recommended when peptides prepared on PAL or BAL resins contain tryptophan residues.

Composition of Reagent K

trifluoroacetic acid (82.5% v/v) phenol (5% v/v) water (5% v/v) thioanisole (5% v/v) 1,2-ethanedithiol (2.5% v/v)

Cleavage and Deprotection with Reagent K

1. If necessary, remove and Fmoc protecting groups using the general Fmoc removal procedure. 

2. Suspend the resin in Reagent K (10 mL to 40 mL per gram of peptide resin) 

3. Stir at room temperature for 1 to 2.5 hours. Peptides containing multiple arginine residues may require longer for complete deprotection. 

4. Filter and rinse the resin with trifluoroacetic acid. 

5. Concentrate the combined filtrates to a syrup under reduced pressure. 

6. Dissolve the syrup in a minimum volume of trifluoroacetic acid. 

7. Add the solution to methyl t-butyl ether (approximately 300:1 v/v methyl t-butyl ether: peptide solution). Filter or centrifuge to collect the crude peptide.