A series of chiral beta(3)-aminoxy acids or amides with various side chains have been synthesized via two different approaches. One is the Arndt-Eistert homologation approach, using chiral alpha-aminoxy acids as starting materials. The other approach, utilizing the enantioselective reduction of beta-keto esters catalyzed by baker's yeast or chiral Ru(II) complexes, produces chiral beta(3)-aminoxy acids with nonproteinaceous side chains. The oligomers of beta(3)-aminoxy acids can be readily prepared using EDCI/HOAt as the coupling reagent.
An effective method was developed to use an enzyme in ionic liquids; the asymmetricreduction of ketones by Geotrichumcandidum in ionic liquids proceeded smoothly with excellent enantioselectivity when the cell was immobilized on water-absorbing polymer containing water, while the reaction without the polymer did not proceed.
An α-acetoxy ketone reducing enzyme has been purified and characterized from the cell-free extract of bakers’ yeast (Saccharomyces cerevisiae). Only one NADPH-dependent dehydrogenase that catalyzed the reduction of α-acetoxy ketone was found in bakers’ yeast. The molecular weight of the enzyme was estimated to be 36 kDa by SDS-polyacrylamide gel electrophoresis. The enzyme was composed of a single
The enantioselectivity for the reduction of ketones by Geotrichumcandidum NBRC 5767 was improved upon immobilization of the whole cell onto an ion exchange resin with polyallylamine. Furthermore, immobilization of the cell enhanced the stability of the enzyme and enabled a continuous-flow reaction under normal aqueous conditions. The biocatalyst was also applied to the reaction in supercritical carbon
electron-rich derivative of SEGPhos and its application in Ru-catalyzed asymmetric hydrogenation reaction of β-ketoesters are reported. Up to 99.5% ee was achieved. Under solvent-free reaction conditions, acetoacetates could be reduced with good enantioselectivity and high efficiency; a TON of 20 000 was obtained within 3.5 h. The results obtained were comparable to those when SEGPhos was applied.
Axial Chirality Control by 2,4-Pentanediol for the Alternative Synthesis of C<sub>3</sub>*-TunePhos Chiral Diphosphine Ligands and Their Applications in Highly Enantioselective Ruthenium-Catalyzed Hydrogenation of β-Keto Esters
A highly efficient strategy for the synthesis of a series of C3*-TunePhos chiral diphosphine ligands was well established with several remarkable features. The synthetic utility of these ligands was explored for the ruthenium-catalyzed asymmetric hydrogenation of β-keto esters. Up to 99% ee values were achieved for the enantioselectivesynthesis of β-hydroxy acid derivatives, which are very important