1
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Understanding the anomaly of cis-trans isomerism in Pro-His sequence. Bioorg Med Chem Lett 2022; 76:128985. [PMID: 36165914 DOI: 10.1016/j.bmcl.2022.128985] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2022] [Revised: 08/05/2022] [Accepted: 09/06/2022] [Indexed: 11/26/2022]
Abstract
The anomalous absence of cisPro stabilizing CαHαXaa···πAro interactions at Xaa-Pro-Aro exclusively when Aro is His, is understood by NMR structural analyses of model peptides, as due to i → i backbone-side chain C6 H-bond that forms uniquely when Aro is His, which significantly decreases its χ1-g- population essential for CαHαXaa···πAro formation.
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2
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van der Waals interactions to control amide cis– trans isomerism. NEW J CHEM 2022. [DOI: 10.1039/d2nj01457b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We discover the presence of local van der Waals (vdW) interactions at the cis amide bond in crystals of isobutyroyl–Pro–Val–OMe.
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3
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α-Helices propagating from stable nucleators exhibit unconventional thermal folding. FEBS Lett 2021; 595:2942-2949. [PMID: 34716991 DOI: 10.1002/1873-3468.14216] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2021] [Revised: 10/21/2021] [Accepted: 10/22/2021] [Indexed: 11/07/2022]
Abstract
Although the effect of thermal perturbations on protein structure has long been modeled in helical peptides, several details, such as the relation between the thermal stabilities of the propagating and nucleating segments of helices, remain elusive. We had earlier reported on the helix-nucleating propensities of covalent H-bond surrogate-constrained α-turns. Here, we analyze the thermal stabilities of helices that propagate along peptides appended to these α-helix nucleators using their NMR and far-UV CD spectra. Unconventional thermal folding of these helix models reveals that the helical fold in propagating backbones resists thermal perturbations as long as their nucleating template is intact. The threshold temperature of such resistance is also influenced by the extent of similarity between the natures of helical folds in the nucleating and propagating segments. Correlations between helicities and rigidities of helix-nucleating and helix-propagating segments reveal subtle interdependence, which explains cooperativity and residual helix formation during protein folding.
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4
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Hydrogen Bond Surrogate-Constrained Dynamic Antiparallel β-Sheets. Chembiochem 2021; 22:2111-2115. [PMID: 33751754 DOI: 10.1002/cbic.202100028] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2021] [Revised: 03/05/2021] [Indexed: 11/06/2022]
Abstract
Antiparallel β-sheets are important secondary structures within proteins that equilibrate with random-coil states; however, little is known about the exact dynamics of this process. Here, the first dynamic β-sheet models that mimic this equilibrium have been designed by using an H-bond surrogate that introduces constraint and torque into a tertiary amide bond. 2D NMR data sufficiently reveal the structure, kinetics, and thermodynamics of the folding process, thereby leading the way to similar analysis in isolated biologically relevant β-sheets.
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5
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Trimodular Solution‐Phase Protocol for Rapid Large‐Scale Synthesis of Hydrogen Bond Surrogate‐Constrained α‐Helicomimics. European J Org Chem 2021. [DOI: 10.1002/ejoc.202001359] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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6
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Hanudatta S. Atreya (1974-2020). MAGNETIC RESONANCE IN CHEMISTRY : MRC 2021; 59:201-212. [PMID: 33565121 DOI: 10.1002/mrc.5130] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2020] [Accepted: 01/01/2021] [Indexed: 06/12/2023]
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7
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A kinetic method for detecting intramolecular peptide H-bonds. NEW J CHEM 2021. [DOI: 10.1039/d1nj03544d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The current method for the detection of peptide hydrogen bond (PHB) formation places charge donors/acceptors (D/A) at the N-/C-termini of the peptides involved in the putative PHB.
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8
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Helix-Coil Transition at a Glycine Following a Nascent α-Helix: A Synergetic Guidance Mechanism for Helix Growth. J Phys Chem A 2020; 124:7478-7490. [PMID: 32877193 DOI: 10.1021/acs.jpca.0c05489] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
A detailed understanding of forces guiding the rapid folding of a polypeptide from an apparently random coil state to an ordered α-helical structure following the rate-limiting preorganization of the initial three residue backbones into helical conformation is imperative to comprehending and regulating protein folding and for the rational design of biological mimetics. However, several details of this process are still unknown. First, although the helix-coil transition was proposed to originate at the residue level (J. Chem. Phys. 1959, 31, 526-535; J. Chem. Phys. 1961, 34, 1963-1974), all helix-folding studies have only established it between time-averaged bulk states of a long-lived helix and several transiently populated random coils, along the whole helix model sequence. Second, the predominant thermodynamic forces driving either this two-state transition or the faster helix growth following helix nucleation are still unclear. Third, the conformational space of the random coil state is not well-defined unlike its corresponding α-helix. Here we investigate the restrictions placed on the conformational space of a Gly residue backbone, as a result of it immediately succeeding a nascent α-helical turn. Analyses of the temperature-dependent 1D-, 2D-NMR, FT-IR, and CD spectra and GROMACS MD simulation trajectory of a Gly residue backbone following a model α-helical turn, which is artificially rigidified by a covalent hydrogen bond surrogate, reveal that: (i) the α-helical turn guides the ϕ torsion of the Gly exclusively into either a predominantly populated entropically favored α-helical (α-ϕ) state or a scarcely populated random coil (RC-ϕ) state; (ii) the α-ϕ state of Gly in turn favors the stability of the preceding α-helical turn, while the RC-ϕ state disrupts it, revealing an entropy-driven synergetic guidance for helix growth in the residue following helix nucleation. The applicability of a current synergetic guidance mechanism to explain rapid helix growth in folded and unfolded states of proteins and helical peptides is discussed.
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9
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H-Bond Surrogate-Stabilized Shortest Single-Turn α-Helices: sp 2 Constraints and Residue Preferences for the Highest α-Helicities. ACS OMEGA 2020; 5:13902-13912. [PMID: 32566857 PMCID: PMC7301546 DOI: 10.1021/acsomega.0c01277] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/24/2020] [Accepted: 05/20/2020] [Indexed: 05/08/2023]
Abstract
Short α-helical sequences of proteins fail to maintain their native conformation when taken out of their protein context. Several covalent constraints have been designed, including the covalent H-bond surrogate (HBS)-where a peptide backbone i + 4 → i H-bond is replaced by a covalent surrogate-to nucleate α-helix in short sequences (>7 < 15 amino acids). But constraining the shortest sequences (four amino acids) into a single α-helical turn is still a significant challenge. Here, we introduce an HBS model that can be placed in unstructured tetrapeptides without excising any of its residues, and that biases them predominantly into remarkably stable single α-helical turns in varying solvents, pH values, and temperatures. Circular dichroism (CD), Fourier transform infrared (FT-IR) absorption, one-dimensional (1D)-NMR, two-dimensional (2D)-NMR spectral and computational analyses of the HBS-constrained tetrapeptide analogues reveal that (a) the number of sp2 atoms in the HBS-constrained backbone influences their predominance and rigidity in the α-helical conformation; and (b) residue preferences at the unnatural HBS-constrained positions influence their α-helicities, with Moc[GFA]G-OMe (1a) showing the highest known α-helicity (θn→π*MRE ∼-25.3 × 103 deg cm2 dmol-1 at 228 nm) for a single α-helical turn. Current findings benefit chemical biological applications desiring predictable access to single α-helical turns in tetrapeptides.
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10
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Spectral evidence for generic charge → acceptor interactions in carbamates and esters. RSC Adv 2020; 10:11871-11875. [PMID: 35496580 PMCID: PMC9050606 DOI: 10.1039/d0ra00313a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2020] [Accepted: 03/01/2020] [Indexed: 11/21/2022] Open
Abstract
The correlations of the 1H NMR, 13C NMR and FT-IR spectral data from the R–O–C
Created by potrace 1.16, written by Peter Selinger 2001-2019
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O groups in the alkyl carbamates and esters of homologous alcohols reveal R-group-dependent negative charge stabilization at the carbonyl oxygen and their donation to generic acceptors at Cα of even alkyl alcohols (R), which explains several of their apparently anomalous properties. NMR, FT-IR spectral correlations of the R–O–CO groups in carbamates and esters of homologous alcohols (R) reveal R-group-dependent negative charge stabilization at the carbonyl oxygen and its donation to generic acceptors at Cα of even alkyl R.![]()
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11
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Hydrogen bond surrogate stabilized water soluble 310-helix from a disordered pentapeptide containing coded α-amino acids. Tetrahedron Lett 2018. [DOI: 10.1016/j.tetlet.2018.05.029] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
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12
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Exploring the consequences of a representative "disallowed" conformation of Aib on a 3₁₀-helical fold. Biopolymers 2014; 104:21-36. [PMID: 25488434 DOI: 10.1002/bip.22599] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2013] [Revised: 11/28/2014] [Accepted: 12/01/2014] [Indexed: 01/24/2023]
Abstract
The structural effects of a representative "disallowed" conformation of Aib on the 3(10)-helical fold of an octapeptidomimetic are explored. The 1D ((1)H, (13)C) & 2D NMR, FT-IR and CD data reveal that the octapeptide 1, adopts a 3(10)-helical conformation in solution, as it does in its crystal structure. The C-terminal methyl carboxylate (CO2Me) of 1 was modified into an 1,3-oxazine (Oxa) functional group in the peptidomimetic 2. This modification results in the stabilization of the backbone of the C-terminal Aib (Aib*-Oxa) of 2, in a conformation (ϕ, ψ = 180, 0) that is natively disallowed to Aib. Consequent to the presence of this natively disallowed conformation, the 3(10)-helical fold is not disrupted in the body of the peptidomimetic 2. But the structural distortions that do occur in 2 are primarily in residues in the immediate vicinity of the natively disallowed conformation, rather than in the whole peptide body. Non-native electronic effects resulting from modifications in backbone functional groups can be at the origin of stabilizing residues in natively disallowed conformations.
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13
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Synthesis of 5,6-dihydro-4H-1,3-thiazine containing peptide mimics from N-(3-hydroxypropyl)thioamides and epimerization studies. Tetrahedron Lett 2014. [DOI: 10.1016/j.tetlet.2014.06.084] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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14
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Estimation of the 2.05 helix type i→i hydrogen bond energy at Aib∗-Oxa motif: an isodesmic approach. Tetrahedron Lett 2014. [DOI: 10.1016/j.tetlet.2014.04.064] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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15
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Steric and electronic interactions controlling the cis/trans isomer equilibrium at X-pro tertiary amide motifs in solution. Biopolymers 2013; 101:66-77. [DOI: 10.1002/bip.22278] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2013] [Accepted: 04/27/2013] [Indexed: 11/11/2022]
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16
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Crystal-Structure Analysis of cis-X-Pro-Containing Peptidomimetics: Understanding the Steric Interactions at cisX-Pro Amide Bonds. Angew Chem Int Ed Engl 2013. [DOI: 10.1002/ange.201209517] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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17
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Crystal-structure analysis of cis-X-Pro-containing peptidomimetics: understanding the steric interactions at cis X-Pro amide bonds. Angew Chem Int Ed Engl 2013; 52:3935-9. [PMID: 23450815 DOI: 10.1002/anie.201209517] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2012] [Revised: 01/18/2013] [Indexed: 11/08/2022]
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18
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A method for stabilizing the cis prolyl peptide bond: influence of an unusual n→π∗ interaction in 1,3-oxazine and 1,3-thiazine containing peptidomimetics. Tetrahedron Lett 2012. [DOI: 10.1016/j.tetlet.2012.06.031] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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19
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Accessing the disallowed conformations of peptides employing amide-to-imidate modification. Chem Commun (Camb) 2011; 47:9417-9. [PMID: 21773612 DOI: 10.1039/c1cc13515e] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Selective modification of the C-terminal amide in peptides to dihydrooxazine (a novel stable imidate isostere) by intramolecular nucleophilic cyclo-O-alkylation of the corresponding N-(3-bromopropyl)amides results in constraining of the C-terminal residue in natively disallowed conformations both in crystals and in solution.
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20
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Synthesis and Isolation of 5,6-Dihydro-4H-1,3-Oxazine Hydrobromides by Autocyclization of N-(3-Bromopropyl)amides. J Org Chem 2010; 76:680-3. [DOI: 10.1021/jo101955q] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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21
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N-{1-[(3-Bromopropyl)aminocarbonyl]ethyl}-2-(2-nitrobenzenesulfonamido)propionamide. Acta Crystallogr Sect E Struct Rep Online 2009; 65:o2308-9. [PMID: 21577780 PMCID: PMC2970335 DOI: 10.1107/s1600536809034291] [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: 07/24/2009] [Accepted: 08/27/2009] [Indexed: 11/10/2022]
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22
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Free Radical-Mediated Aryl Amination: Convergent Two- and Three-Component Couplings to Chiral 2,3-Disubstituted Indolines. J Org Chem 2008; 73:3040-6. [DOI: 10.1021/jo702523u] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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23
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Cobalt-catalyzed one-pot three-component coupling route to beta-acetamido carbonyl compounds: a general synthetic protocol for gamma-lactams. J Org Chem 2003; 68:4079-82. [PMID: 12737595 DOI: 10.1021/jo020559c] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
An efficient improved procedure for the synthesis of beta-acetamido carbonyl compounds is developed by a cobalt(II) chloride-catalyzed three-component coupling protocol. The procedure is also amenable to the synthesis of gamma-lactams by a three-component coupling reaction with use of 2-carbomethoxybenzaldehyde. The beta-acetamido carbonyl compounds derived from 2-carbomethoxybenzaldehyde are useful intermediates as they can be transformed to the corresponding gamma-lactams on treatment with base.
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24
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Reverse turn induced pi-facial selectivity during polyaniline-supported cobalt(II) salen catalyzed aerobic epoxidation of N-cinnamoyl L-proline derived peptides. J Org Chem 2003; 68:1679-92. [PMID: 12608779 DOI: 10.1021/jo020352j] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A novel chemo- and diastereoselective aerobic epoxidation of the N-cinnamoyl peptides catalyzed by polyaniline-supported cobalt(II) salen (PASCOS) is described. The N-cinnamoyl proline derived peptides 1 show a high pi-facial selectivity during these epoxidations. The origin of this diastereoselectivity in 1 has been attributed to (i) the propensity of the N-cinnamoyl proline amide to exist predominantly as trans rotamer in CDCl3, DMSO-d6, and CH3CN medium and (ii) existence of these peptides as organized structures (gamma- and beta-turns) due to the presence of intramolecular hydrogen bonds. An extensive solution NMR and MD simulation study on 1d and 1f indicates that the origin of the high pi-facial selectivity is due to the well-defined gamma- and beta-turns which result in the hindrance of one face of the cinnamoyl double bond in the transition state of the epoxidation reaction.
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25
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Free radical-mediated aryl amination and its use in a convergent [3 + 2] strategy for enantioselective indoline alpha-amino acid synthesis. J Am Chem Soc 2003; 125:163-8. [PMID: 12515518 DOI: 10.1021/ja0284308] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The scope of aryl radical additions to the nitrogen of azomethines is described. Aryl, trifluoromethyl alkyl, and alpha,beta-unsaturated ketimines engage in regioselective aryl-nitrogen bond formation via 5-exo cyclizations of an aryl radical to azomethine nitrogen. Selectivity for carbon-nitrogen over carbon-carbon bond formation is generally high (>95:5) and competes only with direct aryl radical reduction by stannane (0-10%). Alpha-ketoimines are a promising new class of carbon radical acceptors for which no competitive aryl radical reduction is observed. The reaction conditions are pH-neutral and are therefore among the mildest methods available for amination of an aromatic ring. The ketimines examined did not suffer from competitive reduction by stannane, offering an advantage over the use of diazo and azide functional groups as nitrogen sources for carbon radicals. The free radical-mediated aryl amination was sequenced with the O'Donnell phase transfer-catalyzed enantioselective alkylation strategy of glycinyl imine to provide either enantiomer of indoline alpha-amino acids with high ee. These new constrained phenyl alanine derivatives are now readily available for evaluation across a variety of applications.
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26
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Free radical-mediated vinyl amination: access to N,N-dialkyl enamines and their beta-stannyl and beta-thio derivatives. Org Lett 2002; 4:4197-200. [PMID: 12443057 DOI: 10.1021/ol027064u] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
[reaction: see text] The first examples of free radical-mediated vinyl amination are described by nonconventional vinyl radical addition to azomethine nitrogen. This new vinyl amination protocol is mild and provides convenient synthetic access to nonstabilized N,N-dialkyl enamines and tandem bond-forming processes.
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27
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Synthesis of small cyclic peptides via reverse turn induced ring closing metathesis of tripeptides. J Org Chem 2002; 67:8247-50. [PMID: 12423162 DOI: 10.1021/jo0200320] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A reverse turn induced (gamma/beta-turn) cyclization of tripeptides 1 can be performed in a ring closing metathesis reaction with Grubbs' catalyst to the corresponding cyclic peptides 2. These cyclic peptides may be useful probes as a conformationally constrained mimic of the bioactive conformation of structurally related HIV protease inhibitors.
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28
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Nonconventional carbon additions to azomethines. aryl amination/indoline synthesis by direct aryl radical addition to azomethine nitrogen. Org Lett 2001; 3:1009-11. [PMID: 11277782] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/19/2023]
Abstract
[reaction: see text]. The generality of a new method for aryl amination has been defined. Ketimines derived from o-bromophenethylamine cyclize to the N-substituted indoline when treated with nBu3SnH and a radical initiator. The pH-neutral conditions tolerate base- and acid-sensitive functionality. The observed regioselectivity is nonconventional for addition reactions involving carbon radicals and carbon-heteroatom pi-bonds.
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29
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Nonconventional Carbon Additions to Azomethines. Aryl Amination/Indoline Synthesis by Direct Aryl Radical Addition to Azomethine Nitrogen. Org Lett 2001. [DOI: 10.1021/ol007065r] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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