Chemical Synthesis of Crustacean Insulin-Like Peptide Using a Novel Method to Prevent Methionine Oxidation During Solid Phase Peptide Synthesis

The oxidation of Met residue(s) in peptides and proteins is sometimes found in solid phase peptide synthesis (SPPS). In this study, in order to develop a method to prevent the oxidation of Met during SPPS, various sulfide compounds were added to the solvent and the oxidation rate was measured. As a result, it was found that tetrahydrothiophene (THT) was most efficient for reducing the extent of Met oxidation. THT tended to prevent the oxidation of Met in a concentration-dependent manner, although the oxidation of Met could not be completely prevented even at a concentration of 20% (v/v). On the other hand, when the SPPS in the presence of THT and then reduction of Met(O) to Met with NH₄I were performed, the yield was much improved. These results indicate that the combination of preventing oxidation with THT and reducing Met with NH₄I is effective for the synthesis of peptides containing Met residue(s). Using the method established here, we could synthesize an insulin-like peptide from the kuruma shrimp. This method is likely to be applicable to the synthesis of various Met-containing peptides.