Biocatalysis as a profound tool in the preparation of highly enantiopure β-amino acids

The First Direct Enzymatic Hydrolysis of Alicyclic β-Amino Esters: A Route to Enantiopurecis andtrans β-Amino Acids

The first direct enzymatic method is reported for the synthesis of cis and trans beta-amino acid enantiomers through the lipase-catalyzed enantioselective hydrolysis of alicyclic beta-amino esters in organic media. High enantioselectivities (E usually >100) were observed when the Candida antarctica lipase B catalyzed reactions were performed with H2O (0.5 equivalents) in iPr2O at 65 degrees C. The resolved products, obtained in good yields (>or=42%), could be easily separated.

Bacterial β-peptidyl aminopeptidases: on the hydrolytic degradation of β-peptides

The special chemical and biological features of beta-peptides have been investigated intensively during recent years. Many studies emphasize the restricted biodegradability and the high metabolic stability of this class of compounds. beta-Peptidyl aminopeptidases form the first family of enzymes that hydrolyze a variety of short beta-peptides and beta-amino-acid-containing peptides. All representatives of this family were isolated from Gram-negative bacteria. The substrate specificities of the peptidases vary greatly, but the enzymes have common structural properties, and a similar reaction mechanism can be expected. This review gives an overview on the beta-peptidyl aminopeptidases with emphasis on their biochemical and structural properties. Their possible physiological function is discussed. Functionally and structurally related enzymes are compared to the beta-peptidyl aminopeptidases.

Cloning and characterization of a novel beta-transaminase from Mesorhizobium sp. strain LUK: a new biocatalyst for the synthesis of enantiomerically pure beta-amino acids

A novel beta-transaminase gene was cloned from Mesorhizobium sp. strain LUK. By using N-terminal sequence and an internal protein sequence, a digoxigenin-labeled probe was made for nonradioactive hybridization, and a 2.5-kb gene fragment was obtained by colony hybridization of a cosmid library. Through Southern blotting and sequence analysis of the selected cosmid clone, the structural gene of the enzyme (1,335 bp) was identified, which encodes a protein of 47,244 Da with a theoretical pI of 6.2. The deduced amino acid sequence of the beta-transaminase showed the highest sequence similarity with glutamate-1-semialdehyde aminomutase of transaminase subgroup II. The beta-transaminase showed higher activities toward d-beta-aminocarboxylic acids such as 3-aminobutyric acid, 3-amino-5-methylhexanoic acid, and 3-amino-3-phenylpropionic acid. The beta-transaminase has an unusually broad specificity for amino acceptors such as pyruvate and alpha-ketoglutarate/oxaloacetate. The enantioselectivity of the enzyme suggested that the recognition mode of beta-aminocarboxylic acids in the active site is reversed relative to that of alpha-amino acids. After comparison of its primary structure with transaminase subgroup II enzymes, it was proposed that R43 interacts with the carboxylate group of the beta-aminocarboxylic acids and the carboxylate group on the side chain of dicarboxylic alpha-keto acids such as alpha-ketoglutarate and oxaloacetate. R404 is another conserved residue, which interacts with the alpha-carboxylate group of the alpha-amino acids and alpha-keto acids. The beta-transaminase was used for the asymmetric synthesis of enantiomerically pure beta-aminocarboxylic acids. (3S)-Amino-3-phenylpropionic acid was produced from the ketocarboxylic acid ester substrate by coupled reaction with a lipase using 3-aminobutyric acid as amino donor.

Lipases in β-Dipeptide Synthesis in Organic Solvents

A number of beta-dipeptides were prepared by two-step lipase-catalyzed reactions where N-acetylated beta-amino esters were first activated as 2,2,2-trifluoroethyl esters with Candida antarctica lipase B (CAL-B). The activated esters were then used to acylate beta-amino ester in the presence of Candida antarctica lipase A (CAL-A) in dry Et2O or i-Pr2O. [reaction: see text].