Trimethoxyphenylthio as a Highly Labile Replacement for tert-Butylthio Cysteine Protection in Fmoc Solid Phase Synthesis

Trimethoxyphenylthio (S-Tmp) is described as a novel cysteine protecting group in Fmoc solid phase peptide synthesis replacing the difficult to remove tert-butylthio. S-Tmp and dimethoxyphenylthio (S-Dmp) were successfully used for cysteine protection in a variety of peptides. Moreover, both groups can be removed in 5 min with mild reducing agents. S-Tmp is recommended for cysteine protection, as it yields crude peptides of high purity.