SIDE-REACTIONS IN PEPTIDE-SYNTHESIS .5. O-SULFONATION OF SERINE AND THREONINE DURING REMOVAL OF THE PMC-PROTECTING AND MTR-PROTECTING GROUPS FROM ARGININE RESIDUES IN FMOC-SOLID-PHASE SYNTHESIS

A novel side reaction in Fmoc-solid-phase synthesis, which occurs duri ng removal of protecting groups and detachment from the resin, was elu cidated by investigations on model peptides: During the cleavage of Pm c- or Mtr-protecting groups from arginine residues by trifluoroacetic acid in peptides with O-tert-butyl-protected aliphatic hydroxyamino ac ids, peptides containing O3-sulfo-serine and O3-sulfo-threonine are fo rmed as side-products in high yields, if suitable scavengers are absen t. Subsequent to their isolation and purification, the structures of t hese peptide sulfuric acid mono-esters could unequivocally be proven b y chemical and spectroscopic (MS, NMR, IR) methods.