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.

Relative configuration of Cys-Pro ester peptides in thioester formation

A peptide containing a cysteinyl prolyl ester (CPE) moiety at the C-terminus (CPE peptide) was transformed into a diketopiperazine (DKP) thioester via an intramolecular N-S acyl shift reaction, and was then used for peptide ligation. The difference in reactivity between the CPE peptide stereoisomers was examined. In reactions of the CPE peptides that contained L-Cys-L-Pro or D-Cys-D-Pro, the desired DKP thioester was formed at the preceding amino acid residue. On the other hand, in reactions of the CPE peptides that contained D-Cys-L-Pro or L-Cys-D-Pro, a thiolactone was formed at the C-terminal prolyl ester, and the ligation occurred at the C-terminal Pro residue. Using this reaction, it was possible to efficiently prepare a cyclic peptide.

Peptide Thioester Formation via an Intramolecular N to S Acyl Shift for Peptide Ligation

In chemical protein synthesis, peptide building blocks are prepared by solid-phase peptide synthesis (SPPS), and then connected by chemical ligation methods. The peptide thioester is one of key building blocks used in chemical protein synthesis, and improvements in the Fmoc SPPS procedure for preparing such thioesters would be highly desirable. In this review we focus on a method for peptide thioester synthesis based on the use of an intramolecular N to S acyl shift reaction as a key reaction. Amide and thioester forms at the thiol-containing residue are in equilibrium as a result of a reversible intramolecular acyl shift, which is detectable by 13C NMR. The amide form is favored under neutral conditions, while the thioester predominates under acidic conditions. Thiol auxiliaries can be employed to facilitate the formation of a thioester from an amide via an intramolecular N-S acyl shift, and the peptide thioester is formed after intermolecular transthioesterification in the presence of excess amounts of thiols. Even under neutral conditions, thiol auxiliary-containing peptides can be ligated with a cysteinyl peptide via an intramolecular N-S acyl shift, followed by native chemical ligation (NCL) in a one-pot reaction. These procedures can be applied to the chemical synthesis of proteins which are post-translationally modified.

Synthesis of a membrane protein with two transmembrane regions

A membrane protein with two transmembrane domains was synthesized by means of the thioester method. The F1F0 ATP synthase subunit c (Sub.c), which consists of 79 amino acid residues (MW 8257), was chosen as a target. For synthetic purposes, two building blocks, Boc-[Lys34(Boc)]-Sub.c(1-38)-SCH2CH2CO-Ala and Sub.c(39-79), were synthesized via solid-phase methods using Boc chemistry. RP-HPLC purification conditions for the transmembrane peptide were examined. As a result, a combination of a mixture of formic acid, 1-propanol and water with a phenyl column was found to be useful for separating the transmembrane peptide. The purified building blocks were condensed in DMSO in the presence of silver chloride, 3,4-dihydro-3-hydroxy-4-oxo-1,2,3-benzotriazine (HOOBt), N,N-diisopropylethylamine to give the product, Sub.c, after removal of Boc groups (yield 16%). The yield of the condensation reaction could be improved to 23% by raising the reaction temperature to 50 degrees C, and to 26% when a mixture of chloroform and methanol was used as a solvent.

Polypeptide synthesis using an expressed peptide as a building block for condensation with a peptide thioester: application to the synthesis of phosphorylated p21Max protein(1-101)

An expressed peptide proved to be useful as a building block for the synthesis of a polypeptide via the thioester method. A partially protected peptide segment, for use as a C-terminal building block, could be prepared from a recombinant protein; its N-terminal amino acid residue was transaminated to an alpha-oxoacyl group, the side-chain amino groups were then protected with t-butoxycarbonyl (Boc) groups, and. finally, the alpha-oxoacyl group was removed. On the other hand, an O-phosphoserine-containing peptide thioester was synthesized via a solid-phase method using Boc chemistry. These building blocks were then condensed in the presence of silver ions and an active ester component. During the condensation, epimerization at the condensation site could be suppressed by the use of N,N-dimthylformamide (DMF) as a solvent. Using this strategy, a phosphorylated partial peptide of the p21Max protein, [Ser(PO3H2)2.11]-p21Max(1-101), was successfully synthesized.