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Kubyshkin V, Rubini M. Proline Analogues. Chem Rev 2024; 124:8130-8232. [PMID: 38941181 DOI: 10.1021/acs.chemrev.4c00007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/30/2024]
Abstract
Within the canonical repertoire of the amino acid involved in protein biogenesis, proline plays a unique role as an amino acid presenting a modified backbone rather than a side-chain. Chemical structures that mimic proline but introduce changes into its specific molecular features are defined as proline analogues. This review article summarizes the existing chemical, physicochemical, and biochemical knowledge about this peculiar family of structures. We group proline analogues from the following compounds: substituted prolines, unsaturated and fused structures, ring size homologues, heterocyclic, e.g., pseudoproline, and bridged proline-resembling structures. We overview (1) the occurrence of proline analogues in nature and their chemical synthesis, (2) physicochemical properties including ring conformation and cis/trans amide isomerization, (3) use in commercial drugs such as nirmatrelvir recently approved against COVID-19, (4) peptide and protein synthesis involving proline analogues, (5) specific opportunities created in peptide engineering, and (6) cases of protein engineering with the analogues. The review aims to provide a summary to anyone interested in using proline analogues in systems ranging from specific biochemical setups to complex biological systems.
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Affiliation(s)
| | - Marina Rubini
- School of Chemistry, University College Dublin, Belfield, Dublin 4, Ireland
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2
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Altiti A, He M, VanPatten S, Cheng KF, Ahmed U, Chiu PY, Mughrabi IT, Jabari BA, Burch RM, Manogue KR, Tracey KJ, Diamond B, Metz CN, Yang H, Hudson LK, Zanos S, Son M, Sherry B, Coleman TR, Al-Abed Y. Thiocarbazate building blocks enable the construction of azapeptides for rapid development of therapeutic candidates. Nat Commun 2022; 13:7127. [PMID: 36443291 PMCID: PMC9705435 DOI: 10.1038/s41467-022-34712-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2021] [Accepted: 11/03/2022] [Indexed: 11/29/2022] Open
Abstract
Peptides, polymers of amino acids, comprise a vital and expanding therapeutic approach. Their rapid degradation by proteases, however, represents a major limitation to their therapeutic utility and chemical modifications to native peptides have been employed to mitigate this weakness. Herein, we describe functionalized thiocarbazate scaffolds as precursors of aza-amino acids, that, upon activation, can be integrated in a peptide sequence to generate azapeptides using conventional peptide synthetic methods. This methodology facilitates peptide editing-replacing targeted amino acid(s) with aza-amino acid(s) within a peptide-to form azapeptides with preferred therapeutic characteristics (extending half-life/bioavailability, while at the same time typically preserving structural features and biological activities). We demonstrate the convenience of this azapeptide synthesis platform in two well-studied peptides with short half-lives: FSSE/P5779, a tetrapeptide inhibitor of HMGB1/MD-2/TLR4 complex formation, and bradykinin, a nine-residue vasoactive peptide. This bench-stable thiocarbazate platform offers a robust and universal approach to optimize peptide-based therapeutics.
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Affiliation(s)
- Ahmad Altiti
- Institute of Bioelectronic Medicine, Feinstein Institutes for Medical Research, Northwell Health, Manhasset, NY, USA.
| | - Mingzhu He
- Institute of Bioelectronic Medicine, Feinstein Institutes for Medical Research, Northwell Health, Manhasset, NY, USA
| | - Sonya VanPatten
- Institute of Bioelectronic Medicine, Feinstein Institutes for Medical Research, Northwell Health, Manhasset, NY, USA
| | - Kai Fan Cheng
- Institute of Bioelectronic Medicine, Feinstein Institutes for Medical Research, Northwell Health, Manhasset, NY, USA
| | - Umair Ahmed
- Institute of Bioelectronic Medicine, Feinstein Institutes for Medical Research, Northwell Health, Manhasset, NY, USA
| | - Pui Yan Chiu
- Institute of Molecular Medicine, Feinstein Institutes for Medical Research, Manhasset, NY, USA
| | - Ibrahim T Mughrabi
- Institute of Bioelectronic Medicine, Feinstein Institutes for Medical Research, Northwell Health, Manhasset, NY, USA
| | - Bayan Al Jabari
- Institute of Bioelectronic Medicine, Feinstein Institutes for Medical Research, Northwell Health, Manhasset, NY, USA
| | | | - Kirk R Manogue
- Center for Molecular Innovation, Feinstein Institutes for Medical Research, Manhasset, NY, USA
| | - Kevin J Tracey
- Institute of Bioelectronic Medicine, Feinstein Institutes for Medical Research, Northwell Health, Manhasset, NY, USA
| | - Betty Diamond
- Institute of Molecular Medicine, Feinstein Institutes for Medical Research, Manhasset, NY, USA
| | - Christine N Metz
- Institute of Molecular Medicine, Feinstein Institutes for Medical Research, Manhasset, NY, USA
- Donald and Barbara Zucker School of Medicine at Hofstra/Northwell, Hempstead, NY, USA
| | - Huan Yang
- Institute of Bioelectronic Medicine, Feinstein Institutes for Medical Research, Northwell Health, Manhasset, NY, USA
| | - LaQueta K Hudson
- Donald and Barbara Zucker School of Medicine at Hofstra/Northwell, Hempstead, NY, USA
| | - Stavros Zanos
- Institute of Bioelectronic Medicine, Feinstein Institutes for Medical Research, Northwell Health, Manhasset, NY, USA
| | - Myoungsun Son
- Institute of Molecular Medicine, Feinstein Institutes for Medical Research, Manhasset, NY, USA
| | - Barbara Sherry
- Institute of Molecular Medicine, Feinstein Institutes for Medical Research, Manhasset, NY, USA
| | - Thomas R Coleman
- Center for Molecular Innovation, Feinstein Institutes for Medical Research, Manhasset, NY, USA
| | - Yousef Al-Abed
- Institute of Bioelectronic Medicine, Feinstein Institutes for Medical Research, Northwell Health, Manhasset, NY, USA.
- Center for Molecular Innovation, Feinstein Institutes for Medical Research, Manhasset, NY, USA.
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3
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Härk HH, Troska A, Arujõe M, Burk P, Järv J, Ploom A. Kinetic study of aza-amino acid incorporation into peptide chains: Influence of the steric effect of the side chain. Tetrahedron 2022. [DOI: 10.1016/j.tet.2022.133161] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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4
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Lee YS. Peptidomimetics and Their Applications for Opioid Peptide Drug Discovery. Biomolecules 2022; 12:biom12091241. [PMID: 36139079 PMCID: PMC9496382 DOI: 10.3390/biom12091241] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2022] [Revised: 08/29/2022] [Accepted: 09/02/2022] [Indexed: 11/16/2022] Open
Abstract
Despite various advantages, opioid peptides have been limited in their therapeutic uses due to the main drawbacks in metabolic stability, blood-brain barrier permeability, and bioavailability. Therefore, extensive studies have focused on overcoming the problems and optimizing the therapeutic potential. Currently, numerous peptide-based drugs are being marketed thanks to new synthetic strategies for optimizing metabolism and alternative routes of administration. This tutorial review briefly introduces the history and role of natural opioid peptides and highlights the key findings on their structure-activity relationships for the opioid receptors. It discusses details on opioid peptidomimetics applied to develop therapeutic candidates for the treatment of pain from the pharmacological and structural points of view. The main focus is the current status of various mimetic tools and the successful applications summarized in tables and figures.
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Affiliation(s)
- Yeon Sun Lee
- Department of Pharmacology, College of Medicine, University of Arizona, Tucson, AZ 85724, USA
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5
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Abstract
Azapeptides undergo on-resin, late-stage N-alkylations to install side chains with high chemoselectivity for the hydrazide nitrogen atoms. The major product is the N1-alkylated "azapeptoid", with only small amounts (<10%) of alkylation occurring at the other aza-amino acid nitrogen (N2). Dialkylations are also possible and afford highly functionalized, disubstituted azapeptides with side chains installed on both aza-amino acid nitrogen atoms. The site-selectivity was determined using Edman degradation, MS/MS sequencing, and comparative LCMS and NMR analyses.
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Affiliation(s)
- Maxwell O Bowles
- Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, United States
| | - Caroline Proulx
- Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, United States
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Lubell WD, Hamdane Y, Poupart J. N-Amino-imidazol-2-one (Nai) Residues as Tools for Peptide Mimicry: Synthesis, Conformational Analysis and Biomedical Applications. SYNTHESIS-STUTTGART 2022. [DOI: 10.1055/s-0040-1719862] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
Abstract
N-Amino-imidazol-2-one (Nai) residues are tools for studying peptide-backbone and side-chain conformation and function. Recent methods for substituted Nai residue synthesis, conformational analysis by X-ray crystallography and computation, and biomedical applications are reviewed, demonstrating the utility of this constrained residue to favor biologically active turn conformers with defined χ-dihedral angle orientations.1 Introduction2 Synthetic Methods3 Conformational Analysis4 Biomedical Applications5 Conclusions
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7
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Bowles M, Proulx C. Solid phase submonomer azapeptide synthesis. Methods Enzymol 2021; 656:169-190. [PMID: 34325786 DOI: 10.1016/bs.mie.2021.04.020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
Azapeptides contain at least one aza-amino acid, where the α-carbon has been replaced by a nitrogen atom, and have found broad applicability in fields ranging from medicinal chemistry to biomaterials. In this chapter, we provide a step-by-step protocol for the solid phase submonomer synthesis of azapeptides, which includes three steps: (1) hydrazone activation and coupling onto a resin-bound peptide, (2) chemoselective semicarbazone functionalization for installation of the aza-amino acid side chain, and (3) orthogonal deprotection of the semicarbazone to complete the monomer addition cycle. We focus on semicarbazone functionalization by N-alkylation with primary alkyl halides, and describe conditions for coupling onto aza-amino acids. Such divergent methods accelerate the synthesis of peptidomimetics and allow the rapid introduction of a wide variety of natural and unnatural side chains directly on solid support using easily accessible submonomers.
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Affiliation(s)
- Maxwell Bowles
- Department of Chemistry, North Carolina State University, Raleigh, NC, United States
| | - Caroline Proulx
- Department of Chemistry, North Carolina State University, Raleigh, NC, United States.
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Hamdane Y, Chauhan PS, Vutla S, Mulumba M, Ong H, Lubell WD. 5-Substituted N-Aminoimidazolone Peptide Mimic Synthesis by Organocatalyzed Reactions of Azopeptides and Use in the Analysis of Biologically Active Backbone and Side-Chain Topology. Org Lett 2021; 23:3491-3495. [PMID: 33886343 DOI: 10.1021/acs.orglett.1c00936] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Fifteen N-aminoimidazolone (Nai) dipeptides having a variety of 5-position side-chain groups were synthesized by regioselective proline-catalyzed reactions of azopeptide and aldehyde components followed by acid-mediated dehydration of an aza-aspartate semialdehyde intermediate. The introduction of 5-aryl-Nai dipeptides into cluster of differentiation 36 receptor (CD36) peptide ligands has provided insight into the conformation responsible for binding affinity and anti-inflammatory activity.
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Liu JY, Sun XY, Tang Q, Song JJ, Li XQ, Gong B, Liu R, Lu ZL. An unnatural tripeptide structure containing intramolecular double H-bonds mimics a turn hairpin conformation. Org Biomol Chem 2021; 19:4359-4363. [PMID: 33908557 DOI: 10.1039/d1ob00526j] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
A series of unnatural tripeptides, each consisting of two aromatic γ-amino acid residues and an ϖ-amino acid residue, are designed to probe their folding into hairpin conformations. The ϖ-amino acid residues, with aliphatic or aromatic spacers of different sizes, serve as the loop of the hairpins. Studies based on one-dimensional (1D) 1H NMR performed at different concentrations, solvent polarity, and temperature, along with 2D-NMR studies, demonstrated that the doubly H-bonded aromatic γ-amino acid residues play important roles in driving these tripeptides into the hairpin conformation. The loop based on 5-aminovaleric acid, which offers a four-carbon (CH2)4 spacer, enhanced the stability of the corresponding hairpin, while loops having a shorter, a longer and a more rigid spacer disfavored the formation of the hairpins. Results from computational studies are in good agreement with the experimental observations. Furthermore, the crystal structure of peptide 1b revealed the expected hairpin conformation in the solid state. This turn motif, which contains H-bonded aromatic γ-amino acid residues as the core unit and an ϖ-amino acid residue serving as the loop, provides a new platform that can be used to obtain a variety of turn conformations by incorporating diverse amino acids into the loops.
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Affiliation(s)
- Jin-Yu Liu
- Key Laboratory of Radiopharmaceuticals, MOE; College of Chemistry, Beijing Normal University, Xinjiekouwai Street 19, Beijing 100875, China.
| | - Xue-Yi Sun
- Key Laboratory of Radiopharmaceuticals, MOE; College of Chemistry, Beijing Normal University, Xinjiekouwai Street 19, Beijing 100875, China.
| | - Quan Tang
- Key Laboratory of Radiopharmaceuticals, MOE; College of Chemistry, Beijing Normal University, Xinjiekouwai Street 19, Beijing 100875, China.
| | - Jun-Jie Song
- Key Laboratory of Radiopharmaceuticals, MOE; College of Chemistry, Beijing Normal University, Xinjiekouwai Street 19, Beijing 100875, China.
| | - Xiao-Qi Li
- Key Laboratory of Radiopharmaceuticals, MOE; College of Chemistry, Beijing Normal University, Xinjiekouwai Street 19, Beijing 100875, China.
| | - Bing Gong
- Department of Chemistry, The State University of New York at Buffalo, Buffalo, New York 14260, USA
| | - Rui Liu
- Key Laboratory of Radiopharmaceuticals, MOE; College of Chemistry, Beijing Normal University, Xinjiekouwai Street 19, Beijing 100875, China.
| | - Zhong-Lin Lu
- Key Laboratory of Radiopharmaceuticals, MOE; College of Chemistry, Beijing Normal University, Xinjiekouwai Street 19, Beijing 100875, China.
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10
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Proulx C, Zhang J, Sabatino D, Chemtob S, Ong H, Lubell WD. Synthesis and Biomedical Potential of Azapeptide Modulators of the Cluster of Differentiation 36 Receptor (CD36). Biomedicines 2020; 8:biomedicines8080241. [PMID: 32717955 PMCID: PMC7459725 DOI: 10.3390/biomedicines8080241] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2020] [Revised: 07/15/2020] [Accepted: 07/17/2020] [Indexed: 12/14/2022] Open
Abstract
The innovative development of azapeptide analogues of growth hormone releasing peptide-6 (GHRP-6) has produced selective modulators of the cluster of differentiation 36 receptor (CD36). The azapeptide CD36 modulators curb macrophage-driven inflammation and mitigate atherosclerotic and angiogenic pathology. In macrophages activated with Toll-like receptor-2 heterodimer agonist, they reduced nitric oxide production and proinflammatory cytokine release. In a mouse choroidal explant microvascular sprouting model, they inhibited neovascularization. In murine models of cardiovascular injury, CD36-selective azapeptide modulators exhibited cardioprotective and anti-atherosclerotic effects. In subretinal inflammation models, they altered activated mononuclear phagocyte metabolism and decreased immune responses to alleviate subsequent inflammation-dependent neuronal injury associated with retinitis pigmentosa, diabetic retinopathy and age-related macular degeneration. The translation of GHRP-6 to potent and selective linear and cyclic azapeptide modulators of CD36 is outlined in this review which highlights the relevance of turn geometry for activity and the biomedical potential of prototypes for the beneficial treatment of a wide range of cardiovascular, metabolic and immunological disorders.
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Affiliation(s)
- Caroline Proulx
- Department of Chemistry, North Carolina State University, Raleigh, NC 27695, USA;
| | - Jinqiang Zhang
- Innovative Drug Research Centre, Chongqing Key Laboratory of Natural Product Synthesis and Drug Research, School of Pharmaceutical Sciences, Chongqing University, Chongqing 401331, China;
| | - David Sabatino
- Department of Chemistry and Biochemistry, Seton Hall University, 400 South Orange Ave, South Orange, NJ 07079, USA;
| | - Sylvain Chemtob
- Département d’Ophtalmologie, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, QC H3C3J7, Canada;
| | - Huy Ong
- Faculté de Pharmacie, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, QC H3C3J7, Canada;
| | - William D. Lubell
- Département de Chimie, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, QC H3C3J7, Canada
- Correspondence:
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11
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Dai Y, Yue N, Huang W, Qian H. Fragment synthesis of disulfide-containing peptides. MethodsX 2020; 7:100945. [PMID: 32577409 PMCID: PMC7303597 DOI: 10.1016/j.mex.2020.100945] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2019] [Accepted: 05/27/2020] [Indexed: 11/24/2022] Open
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12
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Millet-Boureima C, Chingle R, Lubell WD, Gamberi C. Cyst Reduction in a Polycystic Kidney Disease Drosophila Model Using Smac Mimics. Biomedicines 2019; 7:biomedicines7040082. [PMID: 31635379 PMCID: PMC6966561 DOI: 10.3390/biomedicines7040082] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2019] [Revised: 10/11/2019] [Accepted: 10/15/2019] [Indexed: 12/13/2022] Open
Abstract
Autosomal dominant polycystic kidney disease (ADPKD) is an inherited malady affecting 12.5 million people worldwide. Therapeutic options to treat PKD are limited, due in part to lack of precise knowledge of underlying pathological mechanisms. Mimics of the second mitochondria-derived activator of caspases (Smac) have exhibited activity as antineoplastic agents and reported recently to ameliorate cysts in a murine ADPKD model, possibly by differentially targeting cystic cells and sparing the surrounding tissue. A first-in-kind Drosophila PKD model has now been employed to probe further the activity of novel Smac mimics. Substantial reduction of cystic defects was observed in the Malpighian (renal) tubules of treated flies, underscoring mechanistic conservation of the cystic pathways and potential for efficient testing of drug prototypes in this PKD model. Moreover, the observed differential rescue of the anterior and posterior tubules overall, and within their physiologically diverse intermediate and terminal regions implied a nuanced response in distinct tubular regions contingent upon the structure of the Smac mimic. Knowledge gained from studying Smac mimics reveals the capacity for the Drosophila model to precisely probe PKD pharmacology highlighting the value for such critical evaluation of factors implicated in renal function and pathology.
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Affiliation(s)
| | - Ramesh Chingle
- Département de Chimie, Université de Montréal, Montreal, QC H3T 1J4, Canada.
| | - William D Lubell
- Département de Chimie, Université de Montréal, Montreal, QC H3T 1J4, Canada.
| | - Chiara Gamberi
- Biology Department, Concordia University, Montreal, QC H4B 1R6, Canada.
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Malquin N, Rahgoshay K, Lensen N, Chaume G, Miclet E, Brigaud T. CF 2H as a hydrogen bond donor group for the fine tuning of peptide bond geometry with difluoromethylated pseudoprolines. Chem Commun (Camb) 2019; 55:12487-12490. [PMID: 31566647 DOI: 10.1039/c9cc05771d] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
CF2H-Pseudoprolines obtained from difluoroacetaldehyde hemiacetal and serine are stable proline surrogates. The consequence of the incorporation of the CF2H group is an important decrease of the trans to cis amide bond isomerization energy and a remarkable stabilisation of the cis conformer by an hydrogen bond.
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Affiliation(s)
- N Malquin
- Laboratory of Chemical Biology (LCB, EA 4505), Université de Cergy-Pontoise, 5 Mail Gay-Lussac, 95000 Cergy-Pontoise, France.
| | - K Rahgoshay
- Laboratory of Chemical Biology (LCB, EA 4505), Université de Cergy-Pontoise, 5 Mail Gay-Lussac, 95000 Cergy-Pontoise, France.
| | - N Lensen
- Laboratory of Chemical Biology (LCB, EA 4505), Université de Cergy-Pontoise, 5 Mail Gay-Lussac, 95000 Cergy-Pontoise, France.
| | - G Chaume
- Laboratory of Chemical Biology (LCB, EA 4505), Université de Cergy-Pontoise, 5 Mail Gay-Lussac, 95000 Cergy-Pontoise, France.
| | - E Miclet
- Sorbonne Université, École Normale Supérieure, PSL University, CNRS, Laboratoire des Biomolécules, 75005 Paris, France
| | - T Brigaud
- Laboratory of Chemical Biology (LCB, EA 4505), Université de Cergy-Pontoise, 5 Mail Gay-Lussac, 95000 Cergy-Pontoise, France.
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Aza-Amino Acids Disrupt β-Sheet Secondary Structures. Molecules 2019; 24:molecules24101919. [PMID: 31109055 PMCID: PMC6572070 DOI: 10.3390/molecules24101919] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2019] [Revised: 05/15/2019] [Accepted: 05/17/2019] [Indexed: 01/29/2023] Open
Abstract
Cα to N substitution in aza-amino acids imposes local conformational constraints, changes in hydrogen bonding properties, and leads to adaptive chirality at the nitrogen atom. These properties can be exploited in mimicry and stabilization of peptide secondary structures and self-assembly. Here, the effect of a single aza-amino acid incorporation located in the upper β-strand at a hydrogen-bonded (HB) site of a β-hairpin model peptide (H-Arg-Tyr-Val-Glu-Val-d-Pro-Gly-Orn-Lys-Ile-Leu-Gln-NH2) is reported. Specifically, analogs in which valine3 was substituted for aza-valine3 or aza-glycine3 were synthesized, and their β-hairpin stabilities were examined using Nuclear Magnetic Resonance (NMR) spectroscopy. The azapeptide analogs were found to destabilize β-hairpin formation compared to the parent peptide. The aza-valine3 residue was more disruptive of β-hairpin geometry than its aza-glycine3 counterpart.
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