Two Preparation Methods for Peptide Thioester Containing Tyr(SOH) Residue(s) without the Use of Protecting Group for Sulfate Moiety.

We report two methods for the preparation of peptide thioesters containing Tyr(SOH) residue(s), without use of a protecting group for the sulfate moiety. The first was based on direct thioesterification using carbodiimide on a fully protected peptide acid, prepared on a 2-chlorotrityl (Clt) resin with fluoren-9-ylmethoxycarbonyl (Fmoc)-based solid-phase peptide synthesis (Fmoc-SPPS). Subsequent deprotection of the protecting groups with trifluoroacetic acid (TFA) (0 °C, 4 h) yielded peptide thioesters containing Tyr(SOH) residue(s).