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28 results on '"Hansen, Anna Mette"'

5. Studies towards a total synthesis of manzamine A

Author

Hansen, Anna Mette

Subjects
547.59, QD Chemistry
Abstract

Manzamine A has been isolated from various Okinawa Sponges of the genus Haliclona and was first characterised by Higa and co-workers in 1986. The unusual and synthetically challenging structure consists of a pentacyclic core containing an array of 5-, 6-, 8-, and 13-membered rings with a pendant -carboline unit. The complex structure of manzamine A combined with its biological activities has made it a highly attractive synthetic target. The synthetic endeavors in the Clark group to develop a novel approach towards the total synthesis of manzamine A (i) with the main focus on the synthesis of the ABC ring fragment as advanced intermediates will be disclosed. In the first synthetic approach towards the total synthesis of manzamnine A (i), bicyclic enone iii was constructed from amine ii and served as a model system to validate the proposed intermolecular Diels-Alder reaction. Despite several attempts utilising various dienes, the Diels-Alder adduct was not obtained and an alternative bicyclic system was investigated. After accomplishing the synthesis of the simple AB fragment v from propargylamine (iv), the Diels- Alder reaction was yet again investigated. Due to the failure of the Diels-Alder reaction, this route towards the total synthesis of manzamine A (i) was abandoned. The second approach introduces the conjugate addition reaction towards the total synthesis of manzamine A (i). Instead of the Diels-Alder approach, 1,4 addition to enone v was explored. Initial attempts to perform the 1,4-addition reaction and subsequent aldol condensation reaction afforded the dehydrated aldol condensation products vii via silyl enol ether vi. Additional investigations to prevent the dehydration reaction taking place proved unsuccessful. Thereafter, various methods for the introduction of a substituent in the position to the ketone were investigated. These included alkylation using chloromethyl phenylsulfide, halogenation using NBS or NCS, Rubottom oxidation using DMDO, direct amination using manganese(V) complexes, azidation using sodium azide and CAN as well as aziridination using PhI=NTs. A number of adducts viii-x were succesfully prepared. Finally, the last part of the thesis describes the efforts towards the synthesis of a model system resembling the CD ring-system. The macrocyles xiii and xiv were easily synthesised from dienes xi and xii, although the RCM of diene xi gave rise to isolation problems.

Published
2010

14. Mechanistic evidence for intermolecular radical carbonyl additions promoted by samarium diiodide

Author

Hansen, Anna Mette, Lindsay, Karl B., Antharjanam, P.K. Sudhadevi, Karaffa, Jakob, Daasbjerg, Kim, Flowers, Robert A., II, and Skrydstrup, Troels

Subjects
Radicals (Chemistry) -- Chemical properties, Carbonyl compounds -- Chemical properties, Chemistry
Abstract

Experimental evidence is provided for certain Sm[I.sub.2]-promoted C-C bond-forming reactions, where the intermolecular radical addition to carbonyl compounds can proceed with high efficiency without the intervention of an organosamarium intermediate. Evidence is also provided for the mechanism involving intermolecular alkyl radical addition to carbonyl compounds for the Sm[I.sub.2]-promoted coupling of alpha,beta-unsaturated esters/amides to N-acyl oxazolidinones.

Published
2006

15. Can decarbonylation of acyl radicals be overcome in radical addition reactions? En route to a solution employing N-acyl oxazolidinones and Sml2/H2O

Author

Jensen, Christina M., Lindsay, Karl B., Taaning, Rolf H., Karaffa, Jakob, Hansen, Anna Mette, and Skrydstrup, Troels

Subjects
Electron transport -- Research, Radicals (Chemistry) -- Research, Chemistry
Abstract

A solution is developed for promoting difficult intermolecular acyl radical additions in the absence of a CO atmosphere. The approach takes advantage of the ability of the single electron transfer agent, samarium diiodide, to reduce appropriately functionalized acyl derivatives to their corresponding ketyl radical anions, which subsequently react with acrylamides, acrylates, or acrylonitrile, providing products arising from a formal acyl radical addition.

Published
2005

19. SmI2-promoted intra- and intermolecular C-C bond formation with chiral N-acyl oxazolidinones

Author

Taaning, Rolf H., Thim, Laura, Karaffa, Jacob, Campaña, Araceli G., Hansen, Anna-Mette, Skrydstrup, Troels, and Taaning, Rolf Hejle

Abstract

The suitability of chiral oxazolidinones in the SmI2-mediated C-C bond generation between the imide functionality of an N-acyl oxazolidinone unit and an olefinic radical acceptor, in both inter- and intramolecular reactions, was investigated. It was shown that the products from an Evans asymmetric alkylation can undergo direct carbon-carbon bond formation with an acrylamide providing chiral acyclic ketones in reasonable yields. These examples represent the first transformation of such N-acyl oxazolidinones where this chiral auxiliary is removed under the conditions for ketone formation. 5-exo-trig Cyclization studies were also undertaken with the same type of substrates, providing trans-2,5-disubstituted cyclopentanones in yields of approx. 50%. However, attempts to cyclize heteroatom-containing equivalents were less rewarding.

Published
2008

20. Can decarbonylation of acyl radicals be overcome in radical addition reactions? En route to a solution employing N-acyl oxazolidinones and SmI2/H2O

Author

Jensen, Christina M, Lindsay, Karl B, Taaning, Rolf H, Karaffa, Jakob, Hansen, Anna Mette, Skrydstrup, Troels, and Taaning, Rolf Hejle

Subjects
Addition reaction, Radical, Decarbonylation, General Chemistry, Reaction intermediate, Photochemistry, Biochemistry, Medicinal chemistry, Catalysis, chemistry.chemical_compound, Colloid and Surface Chemistry, Reaction rate constant, Organic reaction, chemistry, Acrylonitrile, Radical disproportionation
Abstract

The application of acyl radicals in radical addition reactions in the absence of a CO atmosphere is generally limited to aryl or alpha-unsubstituted alkyl acyl radicals due to competing decarbonylations where the rate constant for this degradation process surpasses 104 s-1. In this work, a potential solution to avoid the problem of decarbonylations is presented employing N-acyl oxazolidinones which are reduced to acyl radical equivalents in the presence of samarium diiodide and water. In the company of an acrylamide, acrylate, or acrylonitrile, the product from a formal acyl radical addition is obtained in yields up to 87%. Examples are given where the decarbonylation rate constants even exceed 108 s-1. It is proposed that the reaction proceeds via a ketyl-like intermediate.

Published
2005

22. Defining the Molecular Basis for the First Potent and Selective Orthosteric Agonists of the FFA2 Free Fatty Acid Receptor

Author

Hudson, Brian D., primary, Due-Hansen, Maria E., additional, Christiansen, Elisabeth, additional, Hansen, Anna Mette, additional, Mackenzie, Amanda E., additional, Murdoch, Hannah, additional, Pandey, Sunil K., additional, Ward, Richard J., additional, Marquez, Rudi, additional, Tikhonova, Irina G., additional, Ulven, Trond, additional, and Milligan, Graeme, additional

Published
2013
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28. SmI2-promoted intra- and intermolecular C–C bond formation with chiral N-acyl oxazolidinones

Author

Taaning, Rolf H., Thim, Laura, Karaffa, Jacob, Campaña, Araceli G., Hansen, Anna-Mette, and Skrydstrup, Troels

Subjects
*HETEROCYCLIC compounds, *CATALYST supports, *CHEMICAL bonds, *IMIDES, *RADICALS (Chemistry), *ALKYLATION
Abstract

Abstract: The suitability of chiral oxazolidinones in the SmI2-mediated C–C bond generation between the imide functionality of an N-acyl oxazolidinone unit and an olefinic radical acceptor, in both inter- and intramolecular reactions, was investigated. It was shown that the products from an Evans asymmetric alkylation can undergo direct carbon–carbon bond formation with an acrylamide providing chiral acyclic ketones in reasonable yields. These examples represent the first transformation of such N-acyl oxazolidinones where this chiral auxiliary is removed under the conditions for ketone formation. 5-exo-trig Cyclization studies were also undertaken with the same type of substrates, providing trans-2,5-disubstituted cyclopentanones in yields of approx. 50%. However, attempts to cyclize heteroatom-containing equivalents were less rewarding. [Copyright &y& Elsevier]

Published
2008
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