Fmoc-N-Me-Cys(Trt)-OH is a Fmoc-protected derivative of N-methyl cysteine used as a building block to prepare peptide thioesters under acidic conditions. The residue attached to the amino group of N-methylcysteine can migrate to the cysteinyl thiol group, resulting in the formation of a peptide thioester. The introduction of this Fmoc-protected derivative is best achieved using HATU as a coupling reagent in the presence of DIPEA (N, N-Diisopropylethylamine). It can also be used to prepare Fmoc-N-Me-Cys(Trt)-OAllyl intermediate for the solid-phase synthesis of dithiol Triostin A.