Epimerization of Glycal Derivatives by a Cyclopentadienylruthenium Catalyst: Application to Metalloenzymatic DYKAT
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
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.
carbohydrates, dynamic kinetic asymmetric transformation, enzyme catalysis, inversion, NMR spectroscopy
Chemical Sciences Organic Chemistry
IdentifiersURN: urn:nbn:se:su:diva-110176DOI: 10.1002/chem.201403720ISI: 000344358900029OAI: oai:DiVA.org:su-110176DiVA: diva2:787276
FunderSwedish Research CouncilKnut and Alice Wallenberg Foundation