Recent Progress in the Synthetic Methodologies of Peptide Thioesters

Two Preparation Methods for Peptide Thioester Containing Tyr(SO3H) Residue(s) without the Use of Protecting Group for Sulfate Moiety

We report two methods for the preparation of peptide thioesters containing Tyr(SO3H) 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(SO3H) residue(s). Peptide thioesters containing one to three Tyr(SO3H) residue(s), prepared by this method, were used as building blocks for the synthesis of the Nα-Fmoc-protected N-terminal part of P-selectin glycoprotein ligand 1 (PSGL-1) (Fmoc-PSGL-1(43-74)) via silver-ion mediated thioester segment condensation. The other method was based on the thioesterification of peptide azide, derived from a peptide hydrazide prepared on a NH2NH-Clt-resin with Fmoc-SPPS. Peptide thioester containing two Tyr(SO3H) residues, prepared via this alternative method, was used as a building block for the one-pot synthesis of the N-terminal extracellular portion of CC-chemokine receptor 5 (CCR5(9-26)) by native chemical ligation (NCL). The two methods for the preparation of peptide thioesters containing Tyr(SO3H) residue(s) described herein are applicable to the synthesis of various types of sulfopeptides.