Application of newly available bio-reducing agents to the synthesis of chiral hydroxy-β-lactams: model for aldose reductase selectivity

Highly efficient and enantioselective biotransformations of β-lactam carbonitriles and carboxamides and their synthetic applications

Catalyzed by Rhodococcus erythropolis AJ270, a nitrile hydratase and amidase containing microbial whole cell catalyst, a number of racemic 1-arylmethyl- and 1-allyl-4-oxoazetidine-2-carbonitriles and carboxamides underwent efficient transformations under very mild conditions to produce enantiopure functionalized S-amide and R-acid products in excellent yields. While the nitrile hydratase showed good enzyme activity but virtually no enantioselectivity, the amidase displayed high R-enantioselectivity against almost all amide substrates tested. The synthetic applications of the resulting functionalized chiral β-lactam derivatives were demonstrated by the facile preparation of β-lactam-fused heterocyclic compounds.

Asymmetric synthesis of (S)-3-chloro-1-phenyl-1-propanol using Saccharomyces cerevisiae reductase with high enantioselectivity

3-Chloro-1-phenyl-1-propanol is used as a chiral intermediate in the synthesis of antidepressant drugs. Various microbial reductases were expressed in Escherichia coli, and their activities toward 3-chloro-1-phenyl-1-propanone were evaluated. The yeast reductase YOL151W (GenBank locus tag) exhibited the highest level of activity and exclusively generated the (S)-alcohol. Recombinant YOL151W was purified by Ni-nitrilotriacetic acid (Ni-NTA) and desalting column chromatography. It displayed an optimal temperature and pH of 40 degrees C and 7.5-8.0, respectively. The glucose dehydrogenase coupling reaction was introduced as an NADPH regeneration system. NaOH solution was occasionally added to maintain the reaction solution pH within the range of 7.0-7.5. By using this reaction system, the substrate (30 mM) could be completely converted to the (S)-alcohol product with an enantiomeric excess value of 100%. A homology model of YOL151W was constructed based on the structure of Sporobolomyces salmonicolor carbonyl reductase (Protein Data Bank ID: 1Y1P). A docking model of YOL151W with NADPH and 3-chloro-1-phenyl-1-propanone was then constructed, which showed that the cofactor and substrate bound tightly to the active site of the enzyme in the lowest free energy state and explained how the (S)-alcohol was produced exclusively in the reduction process.