Efficient Synthesis of New Fluorinated β-Amino Acid Enantiomers through Lipase-Catalyzed Hydrolysis

An efficient and novel enzymatic method has been developed for the synthesis of β-fluorophenyl-substituted β-amino acid enantiomers through lipase PSIM (Burkholderia cepasia) catalyzed hydrolysis of racemic β-amino carboxylic ester hydrochloride salts 3a–e in iPr₂O at 45 °C in the presence of Et₃N and H₂O. Adequate analytical methods were developed for the enantio-separation of racemic β-amino carboxylic ester hydrochlorides 3a–e and β-amino acids 2a–e. Preparative-scale resolutions furnished unreacted amino esters (R)-4a–e and product amino acids (S)-5a–e with excellent ee values (≥99%) and good chemical yields (>48%).

Exploring the substrate scope of ferulic acid decarboxylase (FDC1) from Saccharomyces cerevisiae

Ferulic acid decarboxylase from Saccharomyces cerevisiae (ScFDC1) was described to possess a novel, prenylated flavin mononucleotide cofactor (prFMN) providing the first enzymatic 1,3-dipolar cycloaddition mechanism. The high tolerance of the enzyme towards several non-natural substrates, combined with its high quality, atomic resolution structure nominates FDC1 an ideal candidate as flexible biocatalyst for decarboxylation reactions leading to synthetically valuable styrenes. Herein the substrate scope of ScFDC1 is explored on substituted cinnamic acids bearing different functional groups (–OCH₃, –CF₃ or –Br) at all positions of the phenyl ring (o−, m−, p−)_, as well as on several biaryl and heteroaryl cinnamic acid analogues or derivatives with extended alkyl chain. It was found that E. coli whole cells expressing recombinant ScFDC1 could transform a large variety of substrates with high conversion, including several bulky aryl and heteroaryl cinnamic acid analogues, that characterize ScFDC1 as versatile and highly efficient biocatalyst. Computational studies revealed energetically favoured inactive binding positions and limited active site accessibility for bulky and non-linear substrates, such as 2-phenylthiazol-4-yl-, phenothiazine-2-yl- and 5-(4-bromophenyl)furan-2-yl) acrylic acids. In accordance with the computational predictions, site-directed mutagenesis of residue I330 provided variants with catalytic activity towards phenothiazine-2-yl acrylic acid and provides a basis for altering the substrate specificity of ScFDC1 by structure based rational design.

One-Pot Lipase-Catalyzed Enantioselective Synthesis of (R)-(-)-N-Benzyl-3-(benzylamino)butanamide: The Effect of Solvent Polarity on Enantioselectivity

The use of the solvent engineering has been applied for controlling the resolution of lipase-catalyzed synthesis of β-aminoacids via Michael addition reactions. The strategy consisted of the thermodynamic control of products at equilibrium using the lipase CalB as a catalyst. The enzymatic chemo- and enantioselective synthesis of (R)-(−)-N-benzyl-3-(benzylamino)butanamide is reported, showing the influence of the solvent on the chemoselectivity of the aza-Michael addition and the subsequent kinetic resolution of the Michael adduct; both processes are catalyzed by CalB and both are influenced by the nature of the solvent medium. This approach allowed us to propose a novel one-pot strategy for the enzymatic synthesis of enantiomerically enriched β-aminoesters and β-aminoacids.

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