An improved deblocking agent for direct Fmoc solid-phase synthesis of peptide thioesters

To synthesize peptide thioesters directly on a solid support for use as substrate analogues for thioesterases in non-ribosomal peptide synthases, we modified a reagent compatible with Fmoc solid-phase peptide synthesis that efficiently removes the protecting group while keeping the thioester intact. The deprotecting reagent, consisting of DBU and HOBt, was successfully used to prepare a decapeptide in high yield.