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Epimerization of Glycal Derivatives by a Cyclopentadienylruthenium Catalyst: Application to Metalloenzymatic DYKAT
Stockholm University, Faculty of Science, Department of Organic Chemistry.
Stockholm University, Faculty of Science, Department of Organic Chemistry.
Stockholm University, Faculty of Science, Department of Organic Chemistry.
Stockholm University, Faculty of Science, Department of Organic Chemistry.
2014 (English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 20, no 45, 14756-14762 p.Article in journal (Refereed) Published
Abstract [en]

Epimerization of a non-anomeric stereogenic center in carbohydrates is an important transformation in the synthesis of natural products. In this study an epimerization procedure of the allylic alcohols of glycals by cyclopentadienylruthenium catalyst 1 is presented. The epimerization of 4,6-O-benzylidene-D-glucal 4 in toluene is rapid, and an equlibrium with its D-allal epimer 5 is established within 5min at room temperature. Exchange rates for allal and glucal formation were determined by 1D H-1 EXSY NMR experiments to be 0.055s(-1) and 0.075s(-1), respectively. For 4-O-benzyl-L-rhamnal 8 the epimerization was less rapid and four days of epimerization was required to achieve equilibration of the epimers at room temperature. The epimerization methodology was subsequently combined with acylating enzymes in a dynamic kinetic asymmetric transformation (DYKAT), giving stereoselective acylation to the desired stereoisomers 12, 13, and 15. The net effect of this process is an inversion of a stereogenic center on the glycal, and yields ranging from 71% to 83% of the epimer were obtained.

Place, publisher, year, edition, pages
Weinheim: Wiley-VCH Verlag GmbH & Co. KGaA , 2014. Vol. 20, no 45, 14756-14762 p.
Keyword [en]
carbohydrates, dynamic kinetic asymmetric transformation, enzyme catalysis, inversion, NMR spectroscopy
National Category
Chemical Sciences Organic Chemistry
Identifiers
URN: urn:nbn:se:su:diva-110176DOI: 10.1002/chem.201403720ISI: 000344358900029OAI: oai:DiVA.org:su-110176DiVA: diva2:787276
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note

AuthorCount:4;

Available from: 2015-02-09 Created: 2014-12-08 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Structure, dynamics and reactivity of carbohydrates: NMR spectroscopic studies
Open this publication in new window or tab >>Structure, dynamics and reactivity of carbohydrates: NMR spectroscopic studies
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The main focus of this thesis is on the ring conformations of carbohydrate molecules; how the conformational equilibria and the rates of the associated interconversions are affected by the molecular constitution and their surroundings.

The conformational equilibria of a group of amine linked pseudodisaccharides, designed as potential glycosidase inhibitors, comprising α-D-altrosides are described in Chapter 3. The OS2 conformation was largely populated, and the ring conformation was found to depend on the charge of the amine functionality.

The conformations of β-D-xylopyranoside derivatives with naphthyl-based aglycones, which are potential anti-cancer agents, are described in chapter 4. Solvent dependent flexibility was observed. Intramolecular hydrogen bonds were concluded to be involved in the stabilization of 1C4 conformers in non-hydrogen bonding solvents of low polarity.

Chapter 5 describes the first measurements of the conformational exchange rates of mannuronic acid ester derivatives between the 4C1 and 1C4 conformations, through DNMR measurements. The relative reactivity of glycosyl triflates as electrophiles in glycosylation reactions were investigated with NMR-based competition experiments.

In Chapter 6, investigations of ruthenium-catalyzed epimerizations of the allylic alcohols of glycal derivatives, and stereoselective synthesis of esters through a DYKAT protocol, are described. The kinetics of the epimerizations were elaborated through different NMR-spectroscopic methods.

Chapter 7 describes additions of NMR chemical shift data of mono- and oligosaccharides to database of the computer program CASPER, and applications thereof.

Place, publisher, year, edition, pages
Stockholm: Department of Organic Chemistry, Stockholm University, 2013. 67 p.
Keyword
Carbohydrates, Conformation, NMR spectroscopy, Hydrogen bond
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-92408 (URN)978-91-7447-730-6 (ISBN)
Public defence
2013-09-20, Magnélisalen, Kemiska Övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Submitted. Paper 5: Manuscript.

Available from: 2013-08-29 Created: 2013-08-02 Last updated: 2016-04-11Bibliographically approved
2. Enzyme- and Transition Metal-Catalyzed Asymmetric Transformations: Application of Enzymatic (D)KR in Enantioselective Synthesis
Open this publication in new window or tab >>Enzyme- and Transition Metal-Catalyzed Asymmetric Transformations: Application of Enzymatic (D)KR in Enantioselective Synthesis
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Dynamic kinetic resolution (DKR) is a powerful method for obtaining compounds with high optical purity. The process relies on the combination of a kinetic resolution with an in situ racemization. In this thesis, a combination of an immobilized hydrolase and a transition metal-based racemization catalyst was employed in DKR to transform racemic alcohols and amines into enantioenriched esters and amides, respectively.

In the first part the DKR of 1,2-amino alcohols with different rings sizes and N-protecting groups is described. We showed that the immobilization method used to support the lipase strongly influenced the stereoselectivity of the reaction.

The second part deals with the DKR of C3-functionalized cyclic allylic alcohols affording the corresponding allylic esters in high yields and high ee’s. The protocol was also extended to include carbohydrate derivatives, leading to inversion of a hydroxyl substituted chiral center on the carbohydrate.

The third part focuses on an improved method for obtaining benzylic primary amines. By using a novel, recyclable catalyst composed of Pd nanoparticles on amino-functionalized mesocellular foam, DKR could be performed at 50 °C. Moreover, Lipase PS was for the first time employed in the DKR of amines.

In the fourth part DKR was applied in the total synthesis of Duloxetine, a compound used in the treatment of major depressive disorder. By performing a six-step synthesis, utilizing DKR in the enantiodetermining step, Duloxetine could be isolated in an overall yield of 37% and an ee >96%.

In the final part we investigated how the enantioselectivty of reactions catalyzed by Candida Antarctica lipase B for δ-substituted alkan-2-ols are influenced by water. The results showed that the enzyme displays much higher enantioselectivity in water than in anhydrous toluene. The effect was rationalized by the creation of a water mediated hydrogen bond in the active site that helps the enzyme form enantiodiscriminating binding modes.

Place, publisher, year, edition, pages
Stockholm: Department of Organic Chemistry, Stockholm University, 2014. 78 p.
Keyword
Dynamic Kinetic Resolution, Kinetic Resolution, Enzyme Catalysis, Asymmetric Synthesis
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-108351 (URN)978-91-7649-008-2 (ISBN)
Public defence
2014-11-27, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrheniusväg 16 B, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Manuscript.

Available from: 2014-11-05 Created: 2014-10-22 Last updated: 2016-04-11Bibliographically approved

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