Method Article

Constructing Cyclic Peptides Using an On-Tether Sulfonium Center

DOI:

10.3791/64289

⸱

September 28th, 2022

 ,  ,  ,  ,  ,  ,  ,  , 
1Pingshan Translational Medicine Center, Shenzhen Bay Laboratory, 2Key Laboratory of Chemical Genomics, School of Chemical Biology and Biotechnology, Peking University Shenzhen Graduate School, 3Department of Radiation Oncology, the First Affiliated Hospital, Anhui Medical University

* These authors contributed equally

In This Article

Summary

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This protocol presents the synthesis of cyclic peptides via bisalkylation between cysteine and methionine and the facile thiol-yne reaction triggered by the propargyl sulfonium center.

Abstract

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In recent years, cyclic peptides have attracted increasing attention in the field of drug discovery due to their excellent biological activities, and, as a consequence, they are now used clinically. It is, therefore, critical to seek effective strategies for synthesizing cyclic peptides to promote their application in the field of drug discovery. This paper reports a detailed protocol for the efficient synthesis of cyclic peptides using on-resin or intramolecular (intermolecular) bisalkylation. Using this protocol, linear peptides were synthesized by taking advantage of solid-phase peptide synthesis with cysteine (Cys) and methionine (Met) coupled simultaneously on the resin. Further, cyclic peptides were synthesized via bisalkylation between Met and Cys using a tunable tether and an on-tether sulfonium center. The whole synthetic route can be divided into three major processes: the deprotection of Cys on the resin, the coupling of the linker, and the cyclization between Cys and Met in a trifluoroacetic acid (TFA) cleavage solution. Furthermore, inspired by the reactivity of the sulfonium center, a propargyl group was attached to the Met to trigger thiol-yne addition and form a cyclic peptide. After that, the crude peptides were dried and dissolved in acetonitrile, separated, and then purified by high-performance liquid chromatography (HPLC). The molecular weight of the cyclic peptide was confirmed by liquid chromatography-mass spectrometry (LC-MS), and the stability of the cyclic peptide combination with the reductant was further confirmed using HPLC. In addition, the chemical shift in the cyclic peptide was analyzed by 1H nuclear magnetic resonance (1H NMR) spectra. Overall, this protocol aimed to establish an effective strategy for synthesizing cyclic peptides.

Introduction

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Protein-protein interactions (PPIs)1 play a pivotal role in drug research and development. Constructing stabilized peptides with a fixed conformation by chemical means is one of the most important methods for developing mimetic motifs of PPIs2. To date, several cyclic peptides that target PPIs have been developed for clinical use3. Most peptides are constrained to an α-helix conformation to decrease the conformational entropy and improve the metabolic stability, target-binding affinity, and cell permeability4,5. In the past 2 decades,....

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Protocol

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1. Equipment preparation

CAUTION: Morpholine, N,N-dimethylformamide (DMF), dichloromethane (DCM), N,N-diisopropylethylamine (DIPEA), TFA, morpholine, piperidine, diethyl ether, and methanol are toxic, volatile, and corrosive. These reagents can harm the human body through inhalation, ingestion, or skin contact. For all chemical experiments, use protective equipment, including disposable gloves, experimental coats, and protective eyeglasses.

  1. Construct all peptide substrates on Rink-amide 4-methylbenzhydrylamine (MBHA) resin by standard manual Fmoc-based solid-phase peptide synthesis (SPPS)29

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Results

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All the linear peptides were synthesized on Rink-amide MBHA resin by standard manual Fmoc solid-phase synthesis. A model cyclic hexapeptide (Ac (cyclo-I)-WMAAAC-NH2) was constructed as described in Figure 5A. Notably, a new on-tether chiral center was generated by Met alkylation, with the two epimers of cyclic peptide (Ia, Ib) confirmed by reverse-phase HPLC. Further, the conversion and ratio of epimers were determined using the integration of reverse-phase HPLC. Cyclic Ac-(cyclo-.......

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Discussion

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The synthetic approach described in this paper provides a method for synthesizing cyclic peptides using Cys and Met in the peptide sequence, in which the basic linear peptides are constructed by common solid-phase peptide synthesis techniques. For the bisalkylation of cyclic peptides between Cys and Met, the whole synthetic route can be divided into three major processes: the deprotection of Cys on the resin, the coupling of the linker, and the cyclization between Cys and Met in a trifluoroacetic acid cleavage solution. .......

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Disclosures

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The authors have nothing to disclose.

Acknowledgements

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We acknowledge financial support from the National Key R&D Program of China (2021YFC2103900); the Natural Science Foundation of China grants (21778009, and 21977010); the Natural Science Foundation of Guangdong Province (2022A1515010996 and 2020A1515010521): the Shenzhen Science and Technology Innovation Committee, (RCJC20200714114433053, JCYJ201805081522131455, and JCYJ20200109140406047); and the Shenzhen-Hong Kong Institute of Brain Science-Shenzhen Fundamental Research Institutions grant (2019SHIBS0004). The authors acknowledge journal support from Chemical Science, The Royal Society of Chemistry for reference 30 and The Journal of Organic Chemistr....

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Materials

List of materials used in this article
NameCompanyCatalog NumberComments
1,3-bis(bromomethyl)-benzenEnergyD0215
1,3-Dimethylbarbituric acidEnergyA46873
1H NMR and HSQCBruker AVANCE-III 400
1-Hydroxybenzotriazole hydrateEnergyE020543
2-(7-azabenzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate (HATU)EnergyA1797
2-mercaptopyridineEnergyY31130
6-Aminocaproic acidEnergyA010678
Acetic anhydrideEnergyA01021454
AcetonitrileAldrich9758
Ammonium carbonateEnergy12980
Dichloromethane (DCM)EnergyW330229
Digital Heating Cooling Drybath Thermo Scientific88880029
Diisopropylethylamine (DIPEA)EnergyW320014
Dimethyl formamide (DMF)EnergyB020051
DithiothreitolEnergyA10027
Electrospray Ionization MassSHIMADZU2020 LC-MS2020
Fmoc-Ala-OHNanjing Peptide Biotech LtdR30101
Fmoc-Arg(Pbf)-OHNanjing Peptide Biotech LtdR30201
Fmoc-Cys(Trt)-OHNanjing Peptide Biotech LtdR30501
Fmoc-Gln(Trt)-OHNanjing Peptide Biotech LtdR30601
Fmoc-Glu(OtBu)-OHNanjing Peptide Biotech LtdR30701
Fmoc-His(Boc)-OHNanjing Peptide Biotech LtdR30902
Fmoc-Ile-OHNanjing Peptide Biotech LtdR31001
Fmoc-Lys(Boc)-OHNanjing Peptide Biotech LtdR31201
Fmoc-Met-OHNanjing Peptide Biotech LtdR31301
Fmoc-Pro-OHNanjing Peptide Biotech LtdR31501
Fmoc-Ser(tBu)-OHNanjing Peptide Biotech LtdR31601
Fmoc-Thr(tBu)-OHNanjing Peptide Biotech LtdR31701
Fmoc-Trp(Boc)-OHNanjing Peptide Biotech LtdR31801
Fmoc-Tyr(tBu)-OHNanjing Peptide Biotech LtdR31901
Fmoc-Val-OHNanjing Peptide Biotech LtdR32001
Formic acidEnergyW810042
High Performance Liquid
Chromatography		SHIMADZULC-2030
MethanolAldrich9758
MorpholineAldrichM109062
N,N'-DiisopropylcarbodiimideEnergyB010023
Ninhydrin ReagentEnergyN7285
Propargyl bromideEnergyW320293
Rink Amide MBHA resinNanjing Peptide Biotech Ltd.
Solid Phase Extraction (SPE) Sample Collection Plates Thermo Scientific60300-403
Tetrakis(triphenylphosphine) palladiumEnergyT1350
Three-way stopcocksBio-Rad7328107
TriethylamineEnergyB010737
Trifluoroacetic acid (TFA)J&K101398
Triisopropylsilane (TIS)EnergyT1533

References

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  1. Arkin, M. R., Tang, Y. Y., Wells, J. A. Small-molecule inhibitors of protein-protein interactions: Progressing toward the reality. Chemistry Biology. 21 (9), 1102-1114 (2014).
  2. Shi, X. D., et al. Reversible....

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Tags

Cyclic Peptide SynthesisOn Tether SulfoniumSolid Phase PeptideBisalkylation CyclizationCysteine Methionine CouplingPeptide CyclizationTrifluoroacetic Acid CleavageHigh Performance Liquid ChromatographyLiquid Chromatography Mass SpectrometryProton NMR Analysis

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