High-yield cleavage of tryptophanyl peptide bonds by o-iodosobenzoic acid

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Abstract
A new procedure to cleave tryptophanyl peptide bonds in high yield is reported. The method involves treatment of the S-alkylated protein with o-iodosobenzoic acid. The procedure is highly selective for tryptophan and does not modify tyrosine or histidine, but may convert methionine to its sulfoxide derivative. The yields in the cleavage are 70-100%. Tryptophanyl bonds to alanine, glycine, serine, threonine, glutamine, arginine and S-(pyridylethyl)cysteine are split in nearly quantitative yield, while those preceding isoleucine or valine are split in .apprx. 70% yield in the proteins examined. The chemical mechanism for tryptophanyl bond cleavage was not defined, but it is likely that oxidation of the indole ring occurs during the reaction with o-iodosobenzoic acid. Some problems with the quality of commercial preparations of the reagent are discussed.