The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
D Biswas - One of the best experts on this subject based on the ideXlab platform.
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synthesis of Oxygen Heterocycles
Tetrahedron Letters, 2006Co-Authors: A K Ganguly, P K Mahata, D BiswasAbstract:A generalised scheme for the synthesis of flavones, flavonones and chromones involving 3-acyl-γ-pyrone intermediates has been developed. Convenient synthesis of other Oxygen Heterocycles using similar procedure have been outlined.
Christine L. Willis - One of the best experts on this subject based on the ideXlab platform.
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a bioinspired strategy for the enantioselective synthesis of bicyclic Oxygen Heterocycles
Organic Letters, 2020Co-Authors: Edith Rodriguez Venegas, Christine L. WillisAbstract:A new strategy is described for the direct conversion of unsaturated 3,5-dihydroxy-diarylheptanoids to dimeric products assembled on trans-2,8-dioxabicyclo[4.4.0]decane frameworks. The key atom-eco...
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A Rieske Oxygenase/epoxide hydrolase-catalysed reaction cascade creates Oxygen Heterocycles in mupirocin biosynthesis
Nature Catalysis, 2018Co-Authors: Luoyi Wang, Alice Parnell, Christopher Williams, Nurfarhanim A. Bakar, Martin R. Challand, Marc W. Van Der Kamp, Thomas J. Simpson, Paul R. Race, Matthew P. Crump, Christine L. WillisAbstract:Mupirocin is a clinically important antibiotic, but the biosynthesis of its tetrahydropyran moiety—an Oxygen heterocycle essential for its bioactivity—has remained elusive. Here, Willis, Crump and co-workers report an enzymatic reaction cascade catalysing this ring formation from a non-activated C–H bond. Oxygen Heterocycles—in particular, tetrahydropyrans (THPs) and tetrahydrofurans—are common structural features of many biologically active polyketide natural products. Mupirocin is a clinically important antibiotic isolated from Pseudomonas fluorescens and is assembled on a THP ring, which is essential for bioactivity. However, the biosynthesis of this moiety has remained elusive. Here, we show an oxidative enzyme-catalysed cascade that generates the THP ring of mupirocin. Rieske non-haem Oxygenase (MupW)-catalysed selective oxidation of the C8–C16 single bond in a complex acyclic precursor is combined with an epoxide hydrolase (MupZ) to catalyse the subsequent regioselective ring formation to give the hydroxylated THP. In the absence of MupZ, a five-membered tetrahydrofuran ring is isolated, and model studies are consistent with cyclization occurring via an epoxide intermediate. High-resolution X-ray crystallographic studies, molecular modelling and mutagenesis experiments of MupZ provide insights into THP ring formation proceeding via an anti-Baldwin 6- endo -tet cyclization.
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a rieske Oxygenase epoxide hydrolase catalysed reaction cascade creates Oxygen Heterocycles in mupirocin biosynthesis
Nature Catalysis, 2018Co-Authors: Luoyi Wang, Christopher Williams, Nurfarhanim A. Bakar, Martin R. Challand, Marc W. Van Der Kamp, Thomas J. Simpson, Paul R. Race, Matthew P. Crump, Alice E Parnell, Christine L. WillisAbstract:Oxygen Heterocycles—in particular, tetrahydropyrans (THPs) and tetrahydrofurans—are common structural features of many biologically active polyketide natural products. Mupirocin is a clinically important antibiotic isolated from Pseudomonas fluorescens and is assembled on a THP ring, which is essential for bioactivity. However, the biosynthesis of this moiety has remained elusive. Here, we show an oxidative enzyme-catalysed cascade that generates the THP ring of mupirocin. Rieske non-haem Oxygenase (MupW)-catalysed selective oxidation of the C8–C16 single bond in a complex acyclic precursor is combined with an epoxide hydrolase (MupZ) to catalyse the subsequent regioselective ring formation to give the hydroxylated THP. In the absence of MupZ, a five-membered tetrahydrofuran ring is isolated, and model studies are consistent with cyclization occurring via an epoxide intermediate. High-resolution X-ray crystallographic studies, molecular modelling and mutagenesis experiments of MupZ provide insights into THP ring formation proceeding via an anti-Baldwin 6-endo-tet cyclization. Mupirocin is a clinically important antibiotic, but the biosynthesis of its tetrahydropyran moiety—an Oxygen heterocycle essential for its bioactivity—has remained elusive. Here, Willis, Crump and co-workers report an enzymatic reaction cascade catalysing this ring formation from a non-activated C–H bond.
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Synthesis of Diarylheptanoid Scaffolds Inspired by Calyxins I and J.
Organic Letters, 2015Co-Authors: Thomas D. Ackrill, Hazel A. Sparkes, Christine L. WillisAbstract:γ,δ-Unsaturated alcohols are prepared efficiently in two steps from o-hydroxycinnamaldehyde. The TMSOTf-mediated reaction of the γ,δ-unsaturated alcohols with aldehydes creates two Oxygen Heterocycles and three new stereocenters in a single pot. The approach is versatile, and by varying the boronic acid, Grignard reagent, and aldehyde, different substituents may be introduced, while use of a chiral base in the conjugate addition gives enantioenriched products.
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bicyclic Oxygen Heterocycles from γ δ unsaturated alcohols synthetic targets inspired by blepharocalyxin d
Angewandte Chemie, 2012Co-Authors: Adam J Bunt, Jon D. Elsworth, Chris D Bailey, Benjamin D Cons, Sophie J Edwards, Tshepo Pheko, Christine L. WillisAbstract:: trans-2,8-Dioxabicyclodecanes were prepared in high yield with the creation of up to three stereocenters in a single pot by the acid-mediated reaction of γ,δ-unsaturated alcohols with aldehydes (see scheme, Bn=benzyl). This versatile reaction enables the stereoselective introduction of substituents at the C3, C4, C7, and C9 positions of the bicyclic framework.
James W Herndon - One of the best experts on this subject based on the ideXlab platform.
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relative asymmetric induction in the intramolecular reaction between alkynes and cyclopropylcarbene chromium complexes stereocontrolled synthesis of five membered rings fused to Oxygen Heterocycles
Journal of Organic Chemistry, 1999Co-Authors: Julius J Matasi, James W HerndonAbstract:Synthesis of cyclopentenone derivatives fused to Oxygen Heterocycles by means of the intramolecular coupling of alkynes and cyclopropylcarbene−chromium complexes has been examined for a variety of cases in which the tethering chain features a stereogenic center. In some cases, this process proceeds with a very high degree of stereoselectivity; however, the extent and direction of relative asymmetric induction is very dependent upon the position of the chiral atom within the tethering chain and the length of the tethering chain. In the best case, featuring a two-carbon tether and a stereogenic center at the homopropargylic position (complex 1N), the heterocyclic ring was produced with 97:3 selectivity for the cis heterocycle (3N). In the worst case, featuring a three-carbon tether and a stereogenic center at the homopropargylic position (complexes 1F and 1I), no stereoselectivity was observed. Improvement in stereoselectivity was noticed when terminal alkynes were replaced by silylated alkynes and when pro...
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Relative Asymmetric Induction in the Intramolecular Reaction between Alkynes and Cyclopropylcarbene−Chromium Complexes: Stereocontrolled Synthesis of Five-Membered Rings Fused to Oxygen Heterocycles
Journal of Organic Chemistry, 1999Co-Authors: Julius J Matasi, James W HerndonAbstract:Synthesis of cyclopentenone derivatives fused to Oxygen Heterocycles by means of the intramolecular coupling of alkynes and cyclopropylcarbene−chromium complexes has been examined for a variety of cases in which the tethering chain features a stereogenic center. In some cases, this process proceeds with a very high degree of stereoselectivity; however, the extent and direction of relative asymmetric induction is very dependent upon the position of the chiral atom within the tethering chain and the length of the tethering chain. In the best case, featuring a two-carbon tether and a stereogenic center at the homopropargylic position (complex 1N), the heterocyclic ring was produced with 97:3 selectivity for the cis heterocycle (3N). In the worst case, featuring a three-carbon tether and a stereogenic center at the homopropargylic position (complexes 1F and 1I), no stereoselectivity was observed. Improvement in stereoselectivity was noticed when terminal alkynes were replaced by silylated alkynes and when pro...
Allison L Choy - One of the best experts on this subject based on the ideXlab platform.
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asymmetric aldol ring closing metathesis strategy for the enantioselective construction of six to nine membered Oxygen Heterocycles
Journal of Organic Chemistry, 1997Co-Authors: Michael T Crimmins, Allison L ChoyAbstract:The ring closing metathesis reaction has rapidly become an important transformation in organic synthesis.1 Examples of many ring sizes with a variety of functional appendages2 have been constructed by this powerful method, largely because of the advent of the functionally tolerant ruthenium3 and molybdenum4 carbene complexes. Even kinetically and thermodynamically disfavored eight-membered rings have been prepared by ringclosing metathesis. However, virtually all5 successful eight-membered ring closures have required the incorporation of cyclic conformational constraints6 or rigid acyclic conformational control elements to avoid formation of dimers or oligomers.7 It is noteworthy that cyclic constrained dienes underwent more efficient ringclosing metathesis to form eight-membered rings when the two olefinic chains were positioned trans on the cyclic constraint than when they were cis.7 Grubbs6a has attributed this effect to a greater difference in energy between the diene and the cyclic olefin in the cissubstituted substrate. We reasoned that dienes with an appropriate acyclic conformational bias might allow eight (or nine)-membered ring formation and avoid the additional strain imposed by a fused ring attached to the newly formed cyclic olefin. We recently reported an asymmetric aldol-ring-closing metathesis strategy for the enantioselective synthesis of the carbocyclic fragment of the nucleoside analogue 1592U89.8 In view of the importance of enantioselective approaches to cyclic ethers of all sizes, particularly eightand nine-membered ring metabolites that are abundant in marine algae,9 an extension of the aldol-metathesis strategy to Oxygen Heterocycles seemed in order. We report here an efficient, general strategy for the asymmetric synthesis of sixto nine-membered cyclic ethers.10
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Asymmetric Aldol−Ring-Closing Metathesis Strategy for the Enantioselective Construction of Six- to Nine-Membered Oxygen Heterocycles
Journal of Organic Chemistry, 1997Co-Authors: Michael T Crimmins, Allison L ChoyAbstract:The ring closing metathesis reaction has rapidly become an important transformation in organic synthesis.1 Examples of many ring sizes with a variety of functional appendages2 have been constructed by this powerful method, largely because of the advent of the functionally tolerant ruthenium3 and molybdenum4 carbene complexes. Even kinetically and thermodynamically disfavored eight-membered rings have been prepared by ringclosing metathesis. However, virtually all5 successful eight-membered ring closures have required the incorporation of cyclic conformational constraints6 or rigid acyclic conformational control elements to avoid formation of dimers or oligomers.7 It is noteworthy that cyclic constrained dienes underwent more efficient ringclosing metathesis to form eight-membered rings when the two olefinic chains were positioned trans on the cyclic constraint than when they were cis.7 Grubbs6a has attributed this effect to a greater difference in energy between the diene and the cyclic olefin in the cissubstituted substrate. We reasoned that dienes with an appropriate acyclic conformational bias might allow eight (or nine)-membered ring formation and avoid the additional strain imposed by a fused ring attached to the newly formed cyclic olefin. We recently reported an asymmetric aldol-ring-closing metathesis strategy for the enantioselective synthesis of the carbocyclic fragment of the nucleoside analogue 1592U89.8 In view of the importance of enantioselective approaches to cyclic ethers of all sizes, particularly eightand nine-membered ring metabolites that are abundant in marine algae,9 an extension of the aldol-metathesis strategy to Oxygen Heterocycles seemed in order. We report here an efficient, general strategy for the asymmetric synthesis of sixto nine-membered cyclic ethers.10
Jonathan W Burton - One of the best experts on this subject based on the ideXlab platform.
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Synthesis of bicyclic tetrahydrofurans from linear precursors using manganese(III) acetate
Organic and Biomolecular Chemistry, 2015Co-Authors: Anne-caroline Chany, Leo B. Marx, Jonathan W BurtonAbstract:We have recently developed methodology based on oxidative radical reactions for the synthesis of [3.3.0]-bicyclic lactones containing both cyclopentanes and γ-lactams along with application of this methodology to the synthesis of natural products and complex molecular architectures. Herein we report an extension of this methodology to the synthesis of Oxygen Heterocycles including bicyclic bis-lactones.
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Synthesis of (+)-obtusenyne
Chemistry - A European Journal, 2008Co-Authors: S. Y.frankie Mak, Miles S. Congreve, Neil R. Curtis, Andrew N. Payne, Andrew J. Wildsmith, Craig L. Francis, John E Davies, Jonathan W Burton, Sofia I. Pascu, Andrew B. HolmesAbstract:An enantioselective synthesis of the halogenated medium-ring ether natural product (+)-obtusenyne is reported which uses the ring expansion of a seven-membered ketene acetal by means of a Claisen rearrangement to construct the core nine-membered Oxygen heterocycle. The trans substituents across the ether linkage were established by using a transition-metal-catalyzed intramolecular hydrosilation reaction of an exo-cyclic enol ether. In addition, a formal synthesis of ent-obtusenyne from 2-deoxy-D-ribose is reported. A number of interesting points regarding the chemistry of medium-ring Oxygen Heterocycles are highlighted.
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manganese iii acetate mediated synthesis of Oxygen Heterocycles influence of copper ii salts on product distribution
Organic and Biomolecular Chemistry, 2004Co-Authors: David G Hulcoop, Helen M Sheldrake, Jonathan W BurtonAbstract:Unsaturated malonates bearing pendant alcohols yield carbocycles tethered to Oxygen Heterocycles on exposure to manganese(III) acetate and an appropriate copper(II) salt.
