Synthesis of orthogonally protected thioamide dipeptides for use in solid-phase peptide synthesis

Orthogonally protected thioamide-containing dipeptides were efficiently and cleanly prepared from the precursor dipeptides using Curphey's method (P₄S₁₀, hexamethyldisiloxane (HMDO), reflux, DCM) in 67–96% isolated yield. This was in contrast to the use of Lawesson's or Berzelius’ reagents where significant issues with reaction non-completion, decomposition and purification were observed. Subsequent clean removal of the dipeptides’ t-butyl ester protecting groups gave thioamide dipeptide acids which were suitable for use in solid-phase peptide synthesis (SPPS).