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Laviós A, Martínez-Pardo P, Sanz-Marco A, Vila C, Pedro JR, Blay G. Synthesis of α,α-Diaryl-α-amino Acid Precursors by Reaction of Isocyanoacetate Esters with o-Quinone Diimides. Org Lett 2023; 25:5608-5612. [PMID: 37486803 PMCID: PMC10853967 DOI: 10.1021/acs.orglett.3c01965] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2023] [Indexed: 07/26/2023]
Abstract
A novel procedure for the synthesis of α,α-diaryl-α-amino acid derivatives has been developed. Silver oxide catalyzes the conjugate addition of α-aryl isocyanoacetates to o-quinone diimide, affording the corresponding α,α-diarylisocyano esters in excellent yields and regioselectivities in short reaction times. Acid hydrolysis of the isocyano group provides the corresponding amino acids bearing a diarylated tetrasubstituted carbon atom. The reaction is also amenable to the synthesis of α-alkyl-α-arylisocyano esters, while the reaction with 3-hydroxy o-quinone diimides provides 4H-benzo[e][1,3]oxazines via a conjugate addition/cyclization process.
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Affiliation(s)
- Adrián Laviós
- Departament
de Química Orgànica, Facultat de Química, Universitat de València, Burjassot E-46100, Spain
| | - Pablo Martínez-Pardo
- Departament
de Química Orgànica, Facultat de Química, Universitat de València, Burjassot E-46100, Spain
| | - Amparo Sanz-Marco
- Departament
de Química Orgànica, Facultat de Química, Universitat de València, Burjassot E-46100, Spain
| | - Carlos Vila
- Departament
de Química Orgànica, Facultat de Química, Universitat de València, Burjassot E-46100, Spain
| | - José R. Pedro
- Departament
de Química Orgànica, Facultat de Química, Universitat de València, Burjassot E-46100, Spain
| | - Gonzalo Blay
- Departament
de Química Orgànica, Facultat de Química, Universitat de València, Burjassot E-46100, Spain
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2
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Zhang K, Liu XF, Zhang WZ, Ren WM, Lu XB. Electrocarboxylation of N-Acylimines with Carbon Dioxide: Access to Substituted α-Amino Acids. Org Lett 2022; 24:3565-3569. [DOI: 10.1021/acs.orglett.2c01267] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Ke Zhang
- State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116024, PR China
| | - Xiao-Fei Liu
- State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116024, PR China
| | - Wen-Zhen Zhang
- State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116024, PR China
| | - Wei-Min Ren
- State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116024, PR China
| | - Xiao-Bing Lu
- State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116024, PR China
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3
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Casanovas J, Nussinov R, Alemán C. Intrinsic conformational preferences of C(alpha,alpha)-dibenzylglycine. J Org Chem 2008; 73:4205-11. [PMID: 18465898 DOI: 10.1021/jo8005528] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The intrinsic conformational preferences of C (alpha,alpha)-dibenzylglycine, a symmetric alpha,alpha-dialkylated amino acid bearing two benzyl substituents on the alpha-carbon atom, have been determined using quantum chemical calculations at the B3LYP/6-31+G(d,p) level. A total of 46 minimum energy conformations were found for the N-acetyl- N'-methylamide derivative, even though only nine of them showed a relative energy lower than 5.0 kcal/mol. The latter involves C 7, C 5, and alpha' backbone conformations stabilized by intramolecular hydrogen bonds and/or N-H...pi interactions. Calculation of the conformational free energies in different environments (gas-phase, carbon tetrachloride, chloroform, methanol, and water solutions) indicates that four different minima (two C 5 and two C 7) are energetically accessible at room temperature in the gas phase, while in methanol and aqueous solutions one such minimum (C 5) becomes the only significant conformation. Comparison with results recently reported for C (alpha,alpha)-diphenylglycine indicates that substitution of phenyl side groups by benzyl enhances the conformational flexibility leading to (i) a reduction of the strain of the peptide backbone and (ii) alleviating the repulsive interactions between the pi electron density of the phenyl groups and the lone pairs of the carbonyl oxygen atoms.
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Affiliation(s)
- Jordi Casanovas
- Departament de Química, Escola Politècnica Superior, Universitat de Lleida, c/Jaume II no. 69, Lleida, Spain.
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4
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Zanuy D, Rodríguez-Ropero F, Nussinov R, Alemán C. Testing β-helix terminal coils stability by targeted substitutions with non-proteogenic amino acids: A molecular dynamics study. J Struct Biol 2007; 160:177-89. [PMID: 17897839 DOI: 10.1016/j.jsb.2007.07.014] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2007] [Revised: 07/25/2007] [Accepted: 07/31/2007] [Indexed: 11/20/2022]
Abstract
The search for new building block templates useful for nanostructures design, targets protein motifs with a wide range of structures. Stabilizing these building blocks when extracted from their natural environment becomes a fundamental goal in order to successfully control their assembly. Targeted replacements of natural residues by conformationally constrained amino acids were shown to be a successful strategy to achieve such stabilization. In this work, the effect of replacing natural amino acids by non-proteogenic residues in a beta-helix building block has been evaluated using extensive molecular dynamics simulations. Here, we focus on systematic substitutions of valine residues present in beta-sheet segments of a beta-helical building block excised from Escherichia coli galactoside acetyltransferase, residues 131-165. Four different types of non-proteogenic amino acids have been considered for substitution: (i) one dehydroamino acid, (ii) two d-amino acids, (iii) one beta-amino acid and (iv) two alpha,alpha-dialkylamino acids. Our results indicate that the ability of non-proteogenic amino acids to stabilize small building block motifs is site-dependent. We conclude that if the replacement does not alter the energy balance between attractive non-covalent interactions and steric hindrance, synthetic residues are suitable candidates to nucleate beta-helix formation.
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Affiliation(s)
- David Zanuy
- Departament d'Enginyeria Química, E. T. S. d'Enginyeria Industrial de Barcelona, Universitat Politècnica de Catalunya, Diagonal 647, Barcelona E-08028, Spain.
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5
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Casanovas J, Zanuy D, Nussinov R, Alemán C. Intrinsic conformational characteristics of alpha,alpha-diphenylglycine. J Org Chem 2007; 72:2174-81. [PMID: 17291048 DOI: 10.1021/jo0624905] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Quantum mechanical calculations at the B3LYP/6-31+G(d,p) level have been used to investigate the intrinsic conformational preferences of alpha,alpha-diphenylglycine, a simple alpha,alpha-dialkylated amino acid bearing two phenyl substituents on the alpha-carbon, in both the gas phase and aqueous solution. Nine minimum energy conformations have been characterized for the N-acetyl-N'-methylamide derivative within a relative energy range of about 9 kcal/mol. The relative stability of these structures is largely influenced by specific backbone...side chain and side chain...side chain interactions that can be attractive (N-H...pi and C-H...pi) or repulsive (C=O...pi). On the other hand, comparison with the minimum energy conformations calculated for alpha-aminoisobutyric acid, in which the two phenyl substituents are replaced by methyl groups, revealed that the bulky aromatic rings of alpha,alpha-diphenylglycine induce strain in the internal geometry of the peptide. Finally, a set of force-field parameters for classical Molecular Mechanics calculations was developed for the investigated amino acid. Molecular Dynamics simulations in aqueous solutions have been carried out to validate the parameters obtained.
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Affiliation(s)
- Jordi Casanovas
- Departament de Química, Escola Politècnica Superior, Universitat de Lleida, Spain.
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6
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Cacciatore I, Di Stefano A, Duprè S, Morera E, Pinnen F, Spirito A. Synthesis and biological evaluation of the disulfide form of the glutathione analogue gamma-(L-glutamyl)-L-cysteinyl-L-aspartyl-L-cysteine. Bioorg Chem 2003; 31:109-21. [PMID: 12729568 DOI: 10.1016/s0045-2068(03)00022-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
By using the chain to chain mode of cyclization the title glutathione analogue (4), containing the 11-membered disulfide ring replacing the native -Cys-Gly fragment, has been synthesized and characterized together with its reduced dithiol form gamma-Glu-Cys-Asp-Cys (5). The activity of (4) with gamma-glutamyl-transferase and glutathione reductase has been evaluated and compared with those of the two conformationally restricted glutathione analogues (2) and (3) previously reported.
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Affiliation(s)
- Ivana Cacciatore
- Dipartimento di Scienze del Farmaco, Università "G D'Annunzio," Via dei Vestini 31, Chieti 66100, Italy
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7
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Kotha S, Halder S, Damodharan L, Pattabhi V. First and unexpected synthesis of macrocyclic cyclophane-based unusual alpha-amino acid derivatives by phosphazene base without high dilution conditions. Bioorg Med Chem Lett 2002; 12:1113-5. [PMID: 11909729 DOI: 10.1016/s0960-894x(02)00068-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
First synthesis of a macrocylic cyclophane-based unusual alpha-amino acid derivative 11 by coupling of ethyl isocyanoacetate with 1,2-bis(4-bromomethylphenyl)ethane under phase-transfer catalysis (PTC) conditions. Phosphazene base such as 2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine (BEMP) is useful to improve the yield of cyclophane derivative without high dilution conditions.
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Affiliation(s)
- Sambasivarao Kotha
- Department of Chemistry, Indian Institute of Technology-Bombay, Powai, Mumbai 400 076, India.
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8
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Structural and mechanistic studies of the copper(II)-assisted ortho-hydroxylation of benzoates by trimethylamine N-oxide. J Organomet Chem 2002. [DOI: 10.1016/s0022-328x(01)01291-8] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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9
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Morera E, Nalli M, Pinnen F, Rossi D, Lucente G. 4-Amino-1,2-dithiolane-4-carboxylic acid (Adt) as cysteine conformationally restricted analogue. Synthetic protocol for Adt containing peptides. Bioorg Med Chem Lett 2000; 10:1585-8. [PMID: 10915057 DOI: 10.1016/s0960-894x(00)00281-x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
An efficient and versatile protocol to incorporate the achiral and C(alpha,alpha)-tetrasubstituted 4-amino-1,2-dithiolane-4-carboxylic acid Adt (1) residue into peptides is described. The 2,2-bis[(benzylthio)methyl]glycine N-carboxy anhydride (5) was found to be the key reactive intermediate from which both Boc-Adt-OMe (8) and the glutathione analogue H-Glu(-Adt-Gly-OH)-OH (12) can be obtained.
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Affiliation(s)
- E Morera
- Centro di Studio per la Chimica del Farmaco del CNR c/o Dipartimento di Studi Farmaceutici, Università degli Studi di Roma La Sapienza, Italy
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10
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Crisma M, Formaggio F, Mezzato S, Toniolo C, Savrda J, Mazaleyrat JP, Wakselman M. Afc can adopt either the fully extended or a turn conformation. Int J Pept Res Ther 2000. [DOI: 10.1007/bf02443571] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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11
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Lombardi A, De Simone G, Galdiero S, Nastri F, Di Costanzo L, Makihira K, Yamada T, Pavone V. The crystal structure of Afc-containing peptides. Biopolymers 2000; 53:150-60. [PMID: 10679619 DOI: 10.1002/(sici)1097-0282(200002)53:2<150::aid-bip5>3.0.co;2-c] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
A systematic structural analysis of Afc (9-amino-fluorene-9-carboxylic acid) containing peptides is here reported. The crystal structures of four fully protected tripeptides containing the Afc residue in position 2: Z-X(1)-Afc(2)-Y(3)-OMe (peptide a: X = Y = Gly; peptide b: X = Aib, C(alpha, alpha)-dimethylglycine, Y = Gly; peptide c: X = Gly, Y = Aib; peptide d: X = Y = Aib) have been solved by x-ray crystallography. All the results suggest that the Afc residue has a high propensity to assume an extended conformation. In fact, the Afc residue adopts an extended conformation in three peptides examined in this paper (peptides a-c). In contrast, Afc was found in a folded conformation, in the 3(10)-helical region, only in the peptide d, in which it is both preceded and followed by the strong helix promoting Aib.
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Affiliation(s)
- A Lombardi
- Centro Interuniversitario di Ricerca su Peptidi Bioattivi, CNR, University of Napoli "Federico II" via Mezzocannone 4, I-80134 Napoli, Italy
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12
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Pavone V, Lombardi A, Saviano M, De Simone G, Nastri F, Maglio O, Omote Y, Yamanaka Y, Yamada T. Conformational behavior of C alpha,alpha-diphenyl glycine: extended conformation in tripeptides containing consecutive D phi G residues. Biopolymers 2000; 53:161-8. [PMID: 10679620 DOI: 10.1002/(sici)1097-0282(200002)53:2<161::aid-bip6>3.0.co;2-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Recent studies on the conformational preferences of the Dphig (C(alpha,alpha)-diphenylglycine) residue showed that this C(alpha,alpha)-disubstituted glycine has a structural versatility. In fact, depending on the nature of the following or preceding residue, Dphig can assume either folded or extended conformations. We have carried out the analysis of the conformational preferences of the Dphig residue in tripeptides containing consecutive Dphig residues. The crystal structures of Z-Dphig-Dphig -Dphig-OMe (a; Z = benzyloxycarbonyl; OMe = methyl ester), Z-Aib-Dphig-Dphig-OMe (b; Aib = alpha-aminoisobutyric acid), and Z-Ac(3)c-Dphig-Dphig-OMe (c; Ac(3)c = alpha-amino-cyclopropan carboxylic acid), are here reported. The Dphig residues adopt the fully extended conformation in the three tripeptides examined. Together with our previous findings on Dphig containing peptides, the structures of the peptides here examined, indicate that the presence of adjacent Dphig residue in the sequence further stabilizes the extended conformation.
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Affiliation(s)
- V Pavone
- Centro Interuniversitario di Ricerca sui Peptidi Bioattivi, CEINGE-Biotecnologie Avanzate, Università of Napoli "Federico II," 80134 Napoli, Italy.
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13
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Savrda J, Mazaleyrat JP, Wakselman M, Formaggio F, Crisma M, Toniolo C. Synthesis, conformational study, and spectroscopic characterization of the cyclic C alpha, alpha-disubstituted glycine 9-amino-9-fluorenecarboxylic acid. J Pept Sci 1999; 5:61-74. [PMID: 10100122 DOI: 10.1002/(sici)1099-1387(199902)5:2<61::aid-psc173>3.0.co;2-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
A series of terminally blocked peptides (to the pentamer level) from L-Ala and the cyclic C alpha, alpha-disubstituted Gly residue Afc and one Gly/Afc dipeptide have been synthesized by solution method and fully characterized. The molecular structure of the amino acid derivative Boc-Afc-OMe and the dipeptide Boc-Afc-Gly-OMe were determined in the crystal state by X-ray diffraction. In addition, the preferred conformation of all of the model peptides was assessed in deuterochloroform solution by FT-IR absorption and 1H-NMR. The experimental data favour the conclusion that the Afc residue tends to adopt either the fully-extended (C5) or a folded/helical structure. In particular, the former conformation is highly populated in solution and is also that found in the crystal state in the two compounds investigated. A comparison with the structural propensities of the strictly related C alpha, alpha-disubstituted Gly residues Ac5c and D phi g is made and the implications for the use of the Afc residue in conformationally constrained analogues of bioactive peptides are briefly examined. A spectroscopic (UV absorption, fluorescence, CD) characterization of this novel aromatic C alpha, alpha-disubstituted Gly residue is also reported.
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Affiliation(s)
- J Savrda
- SIRCOB, Bât, Lavoisier, University of Versailles, France
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14
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Kotha S, Brahmachary E, Sreenivasachary N. Synthesis of constrained α-amino acid derivatives via Diels-Alder approach. Tetrahedron Lett 1998. [DOI: 10.1016/s0040-4039(98)00562-0] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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15
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Pavone V, Lombardi A, Saviano M, Nastri F, Zaccaro L, Maglio O, Pedone C, Omote Y, Yamanaka Y, Yamada T. Conformational behaviour of C(alpha,alpha)-diphenylglycine: folded vs. extended structures in DphiG-containing tripeptides. J Pept Sci 1998; 4:21-32. [PMID: 9523753 DOI: 10.1002/(sici)1099-1387(199802)4:1%3c21::aid-psc125%3e3.0.co;2-a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The crystal structures of three fully protected tripeptides containing the Dphi g residue (C[alpha,alpha]-diphenylglycine) in the central position are reported, namely Z-Gly-Dphi g-Gly-OMe (a), Z-Gly-Dphi g-Aib-OMe (b) and Z-Aib-Dphi g-Aib-OMe (c). The molecular conformations are quite unusual because the Dphi g residue adopts a folded conformation in the 3(10)-helical region when the following residue adopts a folded conformation of opposite handedness (peptides b and c). In contrast, the Dphi g residue adopts the more frequently observed fully extended conformation when the following residue adopts a semi-extended conformation (peptide a). These findings are in agreement with the theoretical calculations on Ac-Dphi g-Aib-NHCH3 and Ac-Aib-Dphi g-NHCH3 also reported in this work.
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Affiliation(s)
- V Pavone
- Centro Interuniversitario di Ricerca sui Peptidi Bioattivi, CEINGE-Biotecnologie Avanzate, Università di Napoli Federico II, Italy
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16
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Pavone V, Lombardi A, Saviano M, Nastri F, Zaccaro L, Maglio O, Pedone C, Omote Y, Yamanaka Y, Yamada T. Conformational behaviour of Cα,α-diphenylglycine: foldedvs. extended structures in DφG-containing tripeptides. J Pept Sci 1998. [DOI: 10.1002/(sici)1099-1387(199802)4:1<21::aid-psc125>3.0.co;2-a] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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17
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Torrini I, Paglialunga Paradisi M, Pagani Zecchini G, Lucente G, Gavuzzo E, Mazza F, Pochetti G, Traniello S, Spisani S. Synthesis, conformation, and biological activity of two fMLP-OMe analogues containing the new 2-[2'-(methylthio)ethyl]methionine residue. Biopolymers 1997; 42:415-26. [PMID: 9283291 DOI: 10.1002/(sici)1097-0282(19971005)42:4<415::aid-bip5>3.0.co;2-t] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The new C alpha-tetrasubstituted alpha-amino acid residue 2-[2'-(methylthio)ethyl]methionine (Dmt) has been introduced into the reference chemotactic tripeptide HCO-Met-Leu-Phe-OMe (fMLP-OMe) in place of the leucine or methionine, respectively. The biological activity of the new analogues [Dmt2]fMLP-OMe (2) and [Dmt1]fMLP-OMe (3) has been determined; whereas 2 is active toward human neutrophils, stimulating directed migration, superoxide anion generation, and lysozyme release, 3 results practically inactive in all tested assays. A conformational analysis on 2 and 3 has been performed in solution by using ir absorption and 1H-nmr. The conformation of 2 was also examined in the crystal by x-ray diffraction methods. Both 2 and 3 adopt fully extended conformation in correspondence with the Dmt residue. Biological and conformational results are discussed and compared with related previously studied models.
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Affiliation(s)
- I Torrini
- Dipartimento di Studi Farmaceutici, Università La Sapienza, Roma, Italy
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18
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Basak A, Schmidt C, Ismail AA, Seidah NG, Chrétien M, Lazure C. Peptidyl substrates containing unnatural amino acid at the P'1 position are potent inhibitors of prohormone convertases. INTERNATIONAL JOURNAL OF PEPTIDE AND PROTEIN RESEARCH 1995; 46:228-37. [PMID: 8537176 DOI: 10.1111/j.1399-3011.1995.tb00594.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
In order to study further the importance of the P'1 residue upon the activity of human PC1 and human furin, two important members of subtilisin/kexin family of enzymes, we have prepared by solid-phase Fmoc or recently introduced FastMoc chemistry a series of 10 peptidyl substrate analogs. The structures of these analogs are based upon the core sequence of pro-mPC1(83-93) namely, D-Tyr-Lys-Glu-Arg-Ser-Lys-Arg-Xaa-Val-Gln-Lys-Asp, where D-Tyr replaces the native L-Tyr residue and Xaa, representing the P'1 position, corresponds to L-Ser or to nonproteinacous amino acids such as Tle, Sarc, MLeu, Aib, D-Tic or L-Tic. Two more analogs with L-Tic at P'1 position but with one amino acid less, namely P5 Glu or P'3 Gln, and one with a Cit residue in place of Arg at P1 site of the dodecapeptide were also obtained. These peptides were all fully characterized by a combination of MS, 1H-NMR and amino acid analysis. In contrast to the Ser analog, which is an excellent substrate for both hPC1 and hfurin, these analogs displayed moderate to strong inhibition of both hPC1 and hfurin activity in a reversible competitive manner. They all exhibited higher potency for hfurin than for hPC1, with an inhibition constant (Ki) ranging from 0.8 to 10 microM and from 1.0 to 170 microM, respectively. Incorporation of L-Tic yielded an analog with a two to four-fold increased inhibition of either enzymes when compared to its D-Tic counterpart, the effect being more pronounced for hPC1 than for hfurin. Comparison of these data with those for the corresponding N-terminal Fmoc protected peptides revealed that the highly hydrophobic N-terminal Fmoc function occupying the P8 position can contribute positively or negatively towards proteinase inhibition depending on the nature of the unnatural amino acid at P'1 and the enzyme used. Finally, none of the analogs was significantly cleaved by either enzyme. FTIR data on these analogs revealed some important structural differences between the substrate and inhibitor analogs, as there appears to be a conformational shift from a more beta-sheet-like structure for the substrates to a more alpha-helical-like structure for the inhibitors.
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Affiliation(s)
- A Basak
- Laboratory of Neuropeptides Structure and Metabolism, Clinical Research Institute of Montréal (Affiliated to the University of Montréal), Québec, Canada
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