51
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Zhang X, Paton RS. Stereoretention in styrene heterodimerisation promoted by one-electron oxidants. Chem Sci 2020; 11:9309-9324. [PMID: 34123173 PMCID: PMC8163378 DOI: 10.1039/d0sc03059g] [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] [Indexed: 12/17/2022] Open
Abstract
Radical cations generated from the oxidation of C
Created by potrace 1.16, written by Peter Selinger 2001-2019
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C π-bonds are synthetically useful reactive intermediates for C–C and C–X bond formation. Radical cation formation, induced by sub-stoichiometric amounts of external oxidant, are important intermediates in the Woodward–Hoffmann thermally disallowed [2 + 2] cycloaddition of electron-rich alkenes. Using density functional theory (DFT), we report the detailed mechanisms underlying the intermolecular heterodimerisation of anethole and β-methylstyrene to give unsymmetrical, tetra-substituted cyclobutanes. Reactions between trans-alkenes favour the all-trans adduct, resulting from a kinetic preference for anti-addition reinforced by reversibility at ambient temperatures since this is also the thermodynamic product; on the other hand, reactions between a trans-alkene and a cis-alkene favour syn-addition, while exocyclic rotation in the acyclic radical cation intermediate is also possible since C–C forming barriers are higher. Computations are consistent with the experimental observation that hexafluoroisopropanol (HFIP) is a better solvent than acetonitrile, in part due to its ability to stabilise the reduced form of the hypervalent iodine initiator by hydrogen bonding, but also through the stabilisation of radical cationic intermediates along the reaction coordinate. A computational study details the mechanism, catalytic cycle and origins of stereoselectivity underlying hole-catalyzed intermolecular alkene heterodimerisation to give unsymmetrical, tetra-substituted cyclobutanes.![]()
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Golec JC, Carter EM, Ward JW, Whittingham WG, Simón L, Paton RS, Dixon DJ. BIMP‐Catalyzed 1,3‐Prototropic Shift for the Highly Enantioselective Synthesis of Conjugated Cyclohexenones. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.202006202] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
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53
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Roagna G, Ascough DMH, Ibba F, Vicini AC, Fontana A, Christensen KE, Peschiulli A, Oehlrich D, Misale A, Trabanco AA, Paton RS, Pupo G, Gouverneur V. Hydrogen Bonding Phase-Transfer Catalysis with Ionic Reactants: Enantioselective Synthesis of γ-Fluoroamines. J Am Chem Soc 2020; 142:14045-14051. [PMID: 32608977 PMCID: PMC7441491 DOI: 10.1021/jacs.0c05131] [Citation(s) in RCA: 31] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
![]()
Ammonium
salts are used as phase-transfer catalysts for fluorination
with alkali metal fluorides. We now demonstrate that these organic
salts, specifically azetidinium triflates, are suitable substrates
for enantioselective ring opening with CsF and a chiral bis-urea catalyst. This process, which highlights the ability of hydrogen
bonding phase-transfer catalysts to couple two ionic reactants, affords
enantioenriched γ-fluoroamines in high yields. Mechanistic studies
underline the role of the catalyst for phase-transfer, and computed
transition state structures account for the enantioconvergence observed
for mixtures of achiral azetidinium diastereomers. The N-substituents
in the electrophile influence the reactivity, but the configuration
at nitrogen is unimportant for the enantioselectivity.
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St John PC, Guan Y, Kim Y, Etz BD, Kim S, Paton RS. Quantum chemical calculations for over 200,000 organic radical species and 40,000 associated closed-shell molecules. Sci Data 2020; 7:244. [PMID: 32694541 PMCID: PMC7374734 DOI: 10.1038/s41597-020-00588-x] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2020] [Accepted: 06/30/2020] [Indexed: 12/19/2022] Open
Abstract
The stabilities of radicals play a central role in determining the thermodynamics and kinetics of many reactions in organic chemistry. In this data descriptor, we provide consistent and validated quantum chemical calculations for over 200,000 organic radical species and 40,000 associated closed-shell molecules containing C, H, N and O atoms. These data consist of optimized 3D geometries, enthalpies, Gibbs free energy, vibrational frequencies, Mulliken charges and spin densities calculated at the M06-2X/def2-TZVP level of theory, which was previously found to have a favorable trade-off between experimental accuracy and computational efficiency. We expect this data to be useful in the further development of machine learning techniques to predict reaction pathways, bond strengths, and other phenomena closely related to organic radical chemistry.
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55
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St John PC, Guan Y, Kim Y, Kim S, Paton RS. Publisher Correction: Prediction of organic homolytic bond dissociation enthalpies at near chemical accuracy with sub-second computational cost. Nat Commun 2020; 11:3066. [PMID: 32528011 PMCID: PMC7289835 DOI: 10.1038/s41467-020-16706-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
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56
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Levy JN, Alegre-Requena JV, Liu R, Paton RS, McNally A. Selective Halogenation of Pyridines Using Designed Phosphine Reagents. J Am Chem Soc 2020; 142:11295-11305. [PMID: 32469220 DOI: 10.1021/jacs.0c04674] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Halopyridines are key building blocks for synthesizing pharmaceuticals, agrochemicals, and ligands for metal complexes, but strategies to selectively halogenate pyridine C-H precursors are lacking. We designed a set of heterocyclic phosphines that are installed at the 4-position of pyridines as phosphonium salts and then displaced with halide nucleophiles. A broad range of unactivated pyridines can be halogenated, and the method is viable for late-stage halogenation of complex pharmaceuticals. Computational studies indicate that C-halogen bond formation occurs via an SNAr pathway, and phosphine elimination is the rate-determining step. Steric interactions during C-P bond cleavage account for differences in reactivity between 2- and 3-substituted pyridines.
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57
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Piou T, Romanov-Michailidis F, Romanova-Michaelides M, Jackson KE, Semakul N, Taggart TD, Newell BS, Rithner CD, Paton RS, Rovis T. Correction to "Correlating Reactivity and Selectivity to Cyclopentadienyl Ligand Properties in Rh(III)-Catalyzed C-H Activation Reactions: An Experimental and Computational Study". J Am Chem Soc 2020; 142:7709. [PMID: 32271011 DOI: 10.1021/jacs.0c00951] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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58
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Hintzen JCJ, Poater J, Kumar K, Al Temimi AHK, Pieters BJGE, Paton RS, Bickelhaupt FM, Mecinović J. Comparison of Molecular Recognition of Trimethyllysine and Trimethylthialysine by Epigenetic Reader Proteins. Molecules 2020; 25:molecules25081918. [PMID: 32326252 PMCID: PMC7221964 DOI: 10.3390/molecules25081918] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2020] [Revised: 04/16/2020] [Accepted: 04/16/2020] [Indexed: 01/31/2023] Open
Abstract
Gaining a fundamental insight into the biomolecular recognition of posttranslationally modified histones by epigenetic reader proteins is of crucial importance to understanding the regulation of the activity of human genes. Here, we seek to establish whether trimethylthialysine, a simple trimethyllysine analogue generated through cysteine alkylation, is a good trimethyllysine mimic for studies on molecular recognition by reader proteins. Histone peptides bearing trimethylthialysine and trimethyllysine were examined for binding with five human reader proteins employing a combination of thermodynamic analyses, molecular dynamics simulations and quantum chemical analyses. Collectively, our experimental and computational findings reveal that trimethylthialysine and trimethyllysine exhibit very similar binding characteristics for the association with human reader proteins, thereby justifying the use of trimethylthialysine for studies aimed at dissecting the origin of biomolecular recognition in epigenetic processes that play important roles in human health and disease.
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59
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Yuan H, Chen PW, Li MY, Zhang Y, Peng ZW, Liu W, Paton RS, Cao C. Effects of substituents X and Y on the NMR chemical shifts of 2-(4-X phenyl)-5-Y pyrimidines. J Mol Struct 2020. [DOI: 10.1016/j.molstruc.2019.127489] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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60
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Liu B, Alegre‐Requena JV, Paton RS, Miyake GM. Cover Feature: Unconventional Reactivity of Ethynylbenziodoxolone Reagents and Thiols: Scope and Mechanism (Chem. Eur. J. 11/2020). Chemistry 2020. [DOI: 10.1002/chem.201905034] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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61
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Liu B, Alegre-Requena JV, Paton RS, Miyake GM. Unconventional Reactivity of Ethynylbenziodoxolone Reagents and Thiols: Scope and Mechanism. Chemistry 2020; 26:2386-2394. [PMID: 31657063 PMCID: PMC7044075 DOI: 10.1002/chem.201904520] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2019] [Indexed: 12/12/2022]
Abstract
1,2-Dithio-1-alkenes are biologically active compounds widely implemented throughout organic synthesis, functional materials, coordination chemistry, and pharmaceuticals. Traditional methods for accessing 1,2-dithio-1-alkenes often demand transition metal catalysts, specialized or air-sensitive ligands, high temperatures, and disulfides (R2 S2 ). Herein, a general and efficient strategy utilizing ethynylbenziodoxolone (EBX) reagents and thiols is presented that results in the formation of 1,2-dithio-1-alkenes with excellent regioselectivity and stereoselectivity through unprecedented reactivity between the EBX and the thiol. This operationally simple procedure utilizes mild conditions, which result in a broad substrate scope and high functional-group tolerance. The observed unexpected reactivity has been rationalized through both experimental results and DFT calculations.
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62
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Porey S, Zhang X, Bhowmick S, Kumar Singh V, Guin S, Paton RS, Maiti D. Alkyne Linchpin Strategy for Drug:Pharmacophore Conjugation: Experimental and Computational Realization of a Meta-Selective Inverse Sonogashira Coupling. J Am Chem Soc 2020; 142:3762-3774. [PMID: 31910623 DOI: 10.1021/jacs.9b10646] [Citation(s) in RCA: 82] [Impact Index Per Article: 20.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The late-stage functionalization (LSF) of pharmaceutical and agrochemical compounds by the site-selective activation of C-H bonds provides access to diverse structural analogs and expands synthetically-accessible chemical space. We report a C-H functionalization LSF strategy that hinges on the use of an alkyne linchpin to assemble conjugates of sp2-rich marketed pharmaceuticals and agrochemicals with sp3-rich 3D fragments and natural products. This is accomplished through a template-assisted inverse Sonogashira reaction that displays high levels of selectivity for the meta position. This protocol is also amenable to distal structural modifications of α-amino acids. The transformation of alkyne functionality to other functional groups further highlights the applicative potential. Computational and experimental mechanistic studies shed light on the detailed mechanism. Turnover-limiting 1,2-migratory insertion of the bromoalkyne coupling partner occurs after relatively fast C-H activation. While this insertion occurs unselectively, regioconvergence results from one of the adducts undergoing a 1,2-trialkylsilyl migration to form the alkynylated product. A heterobimetallic Pd-Ag transition structure is essential for product formation in the β-bromide elimination step.
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63
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Karabiyikoglu S, Brethomé AV, Palacin T, Paton RS, Fletcher SP. Enantiomerically enriched tetrahydropyridine allyl chlorides. Chem Sci 2020. [DOI: 10.1039/d0sc00377h] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Enantiomerically enriched allyl halides are rare due to their configurational lability. Stable piperidine-based allyl chloride enantiomers can be produced via kinetic resolution, and undergo highly enantiospecific catalyst-free substitutions.
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64
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Dan Q, Newmister SA, Klas KR, Fraley AE, McAfoos TJ, Somoza AD, Sunderhaus JD, Ye Y, Shende VV, Yu F, Sanders JN, Brown WC, Zhao L, Paton RS, Houk KN, Smith JL, Sherman DH, Williams RM. Fungal indole alkaloid biogenesis through evolution of a bifunctional reductase/Diels-Alderase. Nat Chem 2019; 11:972-980. [PMID: 31548667 PMCID: PMC6815239 DOI: 10.1038/s41557-019-0326-6] [Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2019] [Accepted: 08/05/2019] [Indexed: 12/25/2022]
Abstract
Prenylated indole alkaloids such as the calmodulin-inhibitory malbrancheamides and anthelmintic paraherquamides possess great structural diversity and pharmaceutical utility. Here, we report complete elucidation of the malbrancheamide biosynthetic pathway accomplished through complementary approaches. These include a biomimetic total synthesis to access the natural alkaloid and biosynthetic intermediates in racemic form and in vitro enzymatic reconstitution to provide access to the natural antipode (+)-malbrancheamide. Reductive cleavage of an L-Pro-L-Trp dipeptide from the MalG non-ribosomal peptide synthetase (NRPS) followed by reverse prenylation and a cascade of post-NRPS reactions culminates in an intramolecular [4+2] hetero-Diels-Alder (IMDA) cyclization to furnish the bicyclo[2.2.2]diazaoctane scaffold. Enzymatic assembly of optically pure (+)-premalbrancheamide involves an unexpected zwitterionic intermediate where MalC catalyses enantioselective cycloaddition as a bifunctional NADPH-dependent reductase/Diels-Alderase. The crystal structures of substrate and product complexes together with site-directed mutagenesis and molecular dynamics simulations demonstrate how MalC and PhqE (its homologue from the paraherquamide pathway) catalyse diastereo- and enantioselective cyclization in the construction of this important class of secondary metabolites.
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65
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Sam Chan HS, Nguyen QNN, Paton RS, Burton JW. Synthesis, Characterization, and Reactivity of Complex Tricyclic Oxonium Ions, Proposed Intermediates in Natural Product Biosynthesis. J Am Chem Soc 2019; 141:15951-15962. [PMID: 31560524 DOI: 10.1021/jacs.9b07438] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Reactive intermediates frequently play significant roles in the biosynthesis of numerous classes of natural products although the direct observation of these biosynthetically relevant species is rare. We present here direct evidence for the existence of complex, thermally unstable, tricyclic oxonium ions that have been postulated as key reactive intermediates in the biosynthesis of numerous halogenated natural products from Laurencia species. Evidence for their existence comes from full characterization of these oxonium ions by low-temperature NMR spectroscopy supported by density functional theory (DFT) calculations, coupled with the direct generation of 10 natural products on exposure of the oxonium ions to various nucleophiles.
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66
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Koniarczyk JL, Greenwood JW, Alegre‐Requena JV, Paton RS, McNally A. A Pyridine–Pyridine Cross‐Coupling Reaction via Dearomatized Radical Intermediates. Angew Chem Int Ed Engl 2019; 58:14882-14886. [DOI: 10.1002/anie.201906267] [Citation(s) in RCA: 43] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2019] [Revised: 07/27/2019] [Indexed: 12/22/2022]
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67
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Koniarczyk JL, Greenwood JW, Alegre‐Requena JV, Paton RS, McNally A. A Pyridine–Pyridine Cross‐Coupling Reaction via Dearomatized Radical Intermediates. Angew Chem Int Ed Engl 2019. [DOI: 10.1002/ange.201906267] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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68
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Brethomé AV, Paton RS, Fletcher SP. Retooling Asymmetric Conjugate Additions for Sterically Demanding Substrates with an Iterative Data-Driven Approach. ACS Catal 2019; 9:7179-7187. [PMID: 32064147 PMCID: PMC7011729 DOI: 10.1021/acscatal.9b01814] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2019] [Revised: 06/27/2019] [Indexed: 12/13/2022]
Abstract
![]()
The
development of catalytic enantioselective methods is routinely
carried out using easily accessible and prototypical substrates. This
approach to reaction development often yields asymmetric methods that
perform poorly using substrates that are sterically or electronically
dissimilar to those used during the reaction optimization campaign.
Consequently, expanding the scope of previously optimized catalytic
asymmetric reactions to include more challenging substrates is decidedly
nontrivial. Here, we address this challenge through the development
of a systematic workflow to broaden the applicability and reliability
of asymmetric conjugate additions to substrates conventionally regarded
as sterically and electronically demanding. The copper-catalyzed asymmetric
conjugate addition of alkylzirconium nucleophiles to form tertiary
centers, although successful for linear alkyl chains, fails for more
sterically demanding linear α,β-unsaturated ketones. Key
to adapting this method to obtain high enantioselectivity was the
synthesis of modified phosphoramidite ligands, designed using quantitative
structure–selectivity relationships (QSSRs). Iterative rounds
of model construction and ligand synthesis were executed in parallel
to evaluate the performance of 20 chiral ligands. The copper-catalyzed
asymmetric addition is now more broadly applicable, even tolerating
linear enones bearing tert-butyl β-substituents.
The presence of common functional groups is tolerated in both nucleophiles
and electrophiles, giving up to 99% yield and 95% ee across 20 examples.
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69
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Paton RS, Bonsall MB. The ecological and epidemiological consequences of reproductive interference between the vectors Aedes aegypti and Aedes albopictus. J R Soc Interface 2019; 16:20190270. [PMID: 31362626 DOI: 10.1098/rsif.2019.0270] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Vector ecology is integral to understanding the transmission of vector-borne diseases, with processes such as reproduction and competition pivotal in determining vector presence and abundance. The arbovirus vectors Aedes aegypti and Aedes albopictus compete as larvae, but this mechanism is insufficient to explain patterns of coexistence and exclusion. Inviable interspecies matings-known as reproductive interference-is another candidate mechanism. Here, we analyse mathematical models of mosquito population dynamics and epidemiology which include two Aedes-specific features of reproductive interference. First, as these mosquitoes use hosts to find mates, reproductive interference will only occur if the same host is visited. Host choice will, in turn, be determined by behavioural responses to host availability. Second, females can become sterilized after mis-mating with heterospecifics. We find that a species with an affinity for a shared host will suffer more from reproductive interference than a less selective competitor. Costs from reproductive interference can be 'traded-off' against costs from larval competition, leading to competitive outcomes that are difficult to predict from empirical evidence. Sterilizations of a self-limiting species can counterintuitively lead to higher densities than a competitor suffering less sterilization. We identify that behavioural responses and reproductive interference mediate a concomitant relationship between vector ecological dynamics and epidemiology. Competitors with opposite behavioural responses can maintain disease where human hosts are rare, due to vector coexistence facilitated by a reduced cost from reproductive interference. Our work elucidates the relative roles of the competitive mechanisms governing Aedes populations and the associated epidemiological consequences.
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70
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Achar TK, Zhang X, Mondal R, Shanavas MS, Maiti S, Maity S, Pal N, Paton RS, Maiti D. Palladium‐Catalyzed Directed
meta
‐Selective C−H Allylation of Arenes: Unactivated Internal Olefins as Allyl Surrogates. Angew Chem Int Ed Engl 2019; 58:10353-10360. [DOI: 10.1002/anie.201904608] [Citation(s) in RCA: 57] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2019] [Revised: 05/15/2019] [Indexed: 12/25/2022]
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71
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Dan Q, Newmister SA, Klas KR, Fraley AE, Paton RS, Houk KN, Williams RM, Sherman DH, Smith JL. Evolution of a bifunctional reductase/Diels–Alderase for fungal indole alkaloid biosynthesis. Acta Crystallogr A Found Adv 2019. [DOI: 10.1107/s0108767319097599] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
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72
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Achar TK, Zhang X, Mondal R, Shanavas MS, Maiti S, Maity S, Pal N, Paton RS, Maiti D. Palladium‐Catalyzed Directed
meta
‐Selective C−H Allylation of Arenes: Unactivated Internal Olefins as Allyl Surrogates. Angew Chem Int Ed Engl 2019. [DOI: 10.1002/ange.201904608] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
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73
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Shepherd ED, Dyson BS, Hak WE, Nguyen QNN, Lee M, Kim MJ, Sohn TI, Kim D, Burton JW, Paton RS. Structure Determination of a Chloroenyne from Laurencia majuscula Using Computational Methods and Total Synthesis. J Org Chem 2019; 84:4971-4991. [PMID: 30977652 PMCID: PMC6503471 DOI: 10.1021/acs.joc.8b02975] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
![]()
Despite numerous
advances in spectroscopic methods through the
latter part of the 20th century, the unequivocal structure determination
of natural products can remain challenging, and inevitably, incorrect
structures appear in the literature. Computational methods that allow
the accurate prediction of NMR chemical shifts have emerged as a powerful
addition to the toolbox of methods available for the structure determination
of small organic molecules. Herein, we report the structure determination
of a small, stereochemically rich natural product from Laurencia majuscula using the powerful combination
of computational methods and total synthesis, along with the structure
confirmation of notoryne, using the same approach. Additionally, we
synthesized three further diastereomers of the L. majuscula enyne and have demonstrated that computations are able to distinguish
each of the four synthetic diastereomers from the 32 possible diastereomers
of the natural product. Key to the success of this work is to analyze
the computational data to provide the greatest distinction between
each diastereomer, by identifying chemical shifts that are most sensitive
to changes in relative stereochemistry. The success of the computational
methods in the structure determination of stereochemically rich, flexible
organic molecules will allow all involved in structure determination
to use these methods with confidence.
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74
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Hilton MC, Zhang X, Boyle BT, Alegre-Requena JV, Paton RS, McNally A. Heterobiaryl synthesis by contractive C-C coupling via P(V) intermediates. Science 2019; 362:799-804. [PMID: 30442804 DOI: 10.1126/science.aas8961] [Citation(s) in RCA: 118] [Impact Index Per Article: 23.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2018] [Revised: 07/03/2018] [Accepted: 09/25/2018] [Indexed: 12/19/2022]
Abstract
Heterobiaryls composed of pyridine and diazine rings are key components of pharmaceuticals and are often central to pharmacological function. We present an alternative approach to metal-catalyzed cross-coupling to make heterobiaryls using contractive phosphorus C-C couplings, also termed phosphorus ligand coupling reactions. The process starts by regioselective phosphorus substitution of the C-H bonds para to nitrogen in two successive heterocycles; ligand coupling is then triggered via acidic alcohol solutions to form the heterobiaryl bond. Mechanistic studies imply that ligand coupling is an asynchronous process involving migration of one heterocycle to the ipso position of the other around a central pentacoordinate P(V) atom. The strategy can be applied to complex drug-like molecules containing multiple reactive sites and polar functional groups, and also enables convergent coupling of drug fragments and late-stage heteroarylation of pharmaceuticals.
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75
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Guin S, Dolui P, Zhang X, Paul S, Singh VK, Pradhan S, Chandrashekar HB, Anjana SS, Paton RS, Maiti D. Iterative Arylation of Amino Acids and Aliphatic Amines via δ‐C(sp
3
)−H Activation: Experimental and Computational Exploration. Angew Chem Int Ed Engl 2019. [DOI: 10.1002/ange.201900479] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
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