The dynamic kinetic resolution of 3-oxo-4-phenyl-β-lactam by recombinant E. coli overexpressing yeast reductase Ara1p

Ni-Catalyzed asymmetric reduction of α-keto-β-lactams via DKR enabled by proton shuttling

Chiral α-hydroxy-β-lactams are key fragments of many bioactive compounds and antibiotics, and the development of efficient synthetic methods for these compounds is of great value. The highly enantioselective dynamic kinetic resolution (DKR) of α-keto-β-lactams was realized via a novel proton shuttling strategy. A wide range of α-keto-β-lactams were reduced efficiently and enantioselectively by Ni-catalyzed asymmetric hydrogenation, providing the corresponding α-hydroxy-β-lactam derivatives with high yields and enantioselectivities (up to 92% yield, up to 94% ee). Deuterium-labelling experiments indicate that phenylphosphinic acid plays a pivotal role in the DKR of α-keto-β-lactams by promoting the enolization process. The synthetic potential of this protocol was demonstrated by its application in the synthesis of a key intermediate of Taxol and (+)-epi-Cytoxazone.

Exploiting Enzymatic Dynamic Reductive Kinetic Resolution (DYRKR) in Stereocontrolled Synthesis

Over the past two decades, the domains of both frontline synthetic organic chemistry and process chemistry and have seen an increase in crosstalk between asymmetric organic/organometallic approaches and enzymatic approaches to stereocontrolled synthesis. This review highlights the particularly auspicious role for dehydrogenase enzymes in this endeavor, with a focus on dynamic reductive kinetic resolutions (DYRKR) to "deracemize" building blocks, often setting two stereocenters in so doing. The scope and limitations of such dehydrogenase-mediated processes are overviewed, as are future possibilities for the evolution of enzymatic DYRKR.

Chiral ligand optimization in the asymmetric zirconium–zinc transmetalation aldehyde addition reaction

The in situ hydrozirconation-transmetalation-aldehyde addition process is a convenient method for the generation of allylic alcohols. Ongoing research has focused on enhancing the enantioselectivity and substrate scope of this process. A chiral beta-amino thiol scaffold was evaluated in the addition reaction. Amino thiols tend to provide the highest ee's, in part due to the higher affinity of sulfur for zinc over zirconium. A class of valine-based thiol ligands was identified to be effective for the formation of enantiomerically enriched allylic alcohols in terms of low ligand loading and high % ee.

Synthesis of docetaxel and butitaxel analogues through kinetic resolution of racemic beta-lactams with 7-O-triethylsilylbaccatin III

The kinetic resolution of racemic cis-4-phenyl- and cis-4-tert-butyl-3-hydroxy-beta-lactam derivatives with 7-O-triethylsilylbaccatin III yielded paclitaxel and butitaxel analogues with high diastereoselectivity. The results demonstrated that the tert-butyldimethylsilyl protecting group at the C3-hydroxy group of the beta-lactams provided optimum kinetic resolution in comparison with the sterically less demanding triethylsilyl group and the larger triisopropylsilyl group. In addition, it was found that the C4 beta-lactam substituents also influenced diastereoselectivity. The C4 tert-butyl-beta-lactams provided better diastereoselectivity than the corresponding C4 phenyl beta-lactams.