Phosphinyl and Phosphinothioyl Amino Acids and Peptides. VII. The Use of the Dimethylphosphinothioyl Group as a Thiol-protecting Group of Cysteine

The use of the dimethylphosphinothioyl (Mpt) group for the protection of the thiol function in the cysteine side-chain was studied. N,S-Bis(Mpt)-l-cysteine was obtained directly by means of a Schotten-Baumann-type reaction of Mpt–Cl with l-cysteine. The S–Mpt group was stable under acidic conditions, except for HBr in acetic acid, and it could be removed by treatment with AgNO3 or Hg(OAc)2 in an aqueous medium. Glutathione was synthesized by utilizing the new S-protecting group.