Evaluation of TiCl4-mediated reduction of methionine sulfoxide in peptides with oxidizable or reducible residues
Pennington, M.W.; Byrnes, M.E.
Peptide Research 8(1): 39-43
1995
ISSN/ISBN: 1040-5704 PMID: 7756753 Document Number: 442841
Reduction of methionine sulfoxide with TiCl-4/NaI is very rapid for simple methionine-containing peptides. The utility of this oxido/reduction system has been evaluated for three model peptides that contain oxidation/reduction-sensitive components such as a disulfide bond and/or a tryptophan residue. Completely specific reduction of methionine sulfoxide without some reduction of the disulfide bond was not possible with TiCl-4/NaI. Reduction of the methionine sulfoxide residue in these model peptides yielded the desired product as the major component (yield ca. 70%) when a reaction time of four minutes was used. Methionine sulfoxide appears to be the most readily reducible species by low valent titanium. The competing side reactions observed were disulfide bond reduction by low valent titanium and/or tryptophan oxidation by the I-2 generated by reduction of the TiCl-4 with NaI. These side reactions became a serious problem when longer reaction times were used. The levels of contaminants generated by these side reactions were observed to increase with time, reducing the yield of the desired product.