Study Of Enzymatic Umpolung Addition Reactions

Chiral nitrogen-containing compounds are widely used in fields such as agricultural chemicals,pharmaceuticals,and daily chemicals.The development of their synthetic routes has always been a research hotspot.Asymmetric catalytic reactions are the best strategy for synthesizing chiral compounds.Enzymes have received great attention as a green and efficient catalyst due to their promiscuity.Some biocatalytic asymmetric synthesis methods have been developed,but they all have limitations,such as low atom economies and involvement of expensive coenzymes.Therefore,it is urgent to develop a new biocatalytic approach for synthesizing chiral nitrogen-containing compounds.Umpolung is a synthetic strategy widely used in organic chemistry that is based on the formation of carbon anions to construct C-C bonds.It has opened up new frontiers for the construction of bioactive molecules.This thesis found that biocatalysts including penicillin G acylase IPGA,transaminase CV2025,and lipase RMIM exhibit catalytic activity for conjugate umpolung addition reactions.10 kinds of substituted imine substrates,17 kinds of α,β-unsaturated ketones and 34 kinds of their corresponding addition standard samples were synthesized by chemical method to expand the substrate scope of IPGA and CV2025 with better catalytic activity.The process of conjugate umpolung addition reactions catalyzed by transaminase CV2025 was briefly discussed.The study showed that the enzyme catalyzed the substituted N-benzyl imine and 1-penten-3-one yields umpolung addition product.However,no such product was observed when the substituted N-benzyl imine isomer,N-phenylmethyleneamine,was used as a substrate,further confirming the substrate underwent umpolung under the action of the enzyme,leading to the addition reaction.Using computer simulation technology,the imine substrate was docked with the protein,and the hydrophilic amino acid residues within 5? around the substrate were selected for alanine scanning.It was found that mutating either H154 or R416 at these sites would significantly decrease catalytic activity,suggesting they may play an important role in the catalytic process.The conjugate addition reaction of nitro compounds catalyzed by IPGA was studied.Using 2(5H)-furanone and 1-nitropropane as raw materials,4-(1-nitropropyl)dihydrofuran-2(3H)-one was synthesized with 69.40% yield,and 4-propyl-dihydrofuran-2-one,the key intermediate of brivaracetam,was obtained by one-step chemical denitroation.This method provides a reference for the synthesis of the key intermediate of brivaracetam.