2-Mercaptopyridine-1-oxide-based peptide coupling reagents

The thiouronium salts S-(1-oxido-2-pyridinyl)-1,1,3,3-tetramethylthiouronium hexafluorophosphate (HOTT) and tetrafluoroborate (TOTT), and S-(1-oxido-2-pyridinyl)-1,3-dimethyl-1,3-trimethylenethiouronium hexafluorophosphate (HODT) and tetrafluoroborate (TODT), prepared from 2-mercaptopyridine-1-oxide and 1,1,3,3-tetramethylurea (TMU) or 1,3-dimethylpropyleneurea (DMPU), have been employed as reagents in solution and solid-phase peptide coupling chemistry. Furthermore, 2-mercaptopyridine-1-oxide has been employed as racemization-reducing additive combined with the new thiouronium salts and other frequently used peptide coupling reagents such as DCC or TBTU.