| 20340152 |
Heck T, Reimer A, Seebach D, Gardiner J, Deniau G, Lukaszuk A, Kohler HP, Geueke B: beta-Aminopeptidase-Catalyzed Biotransformations of beta (2)-Dipeptides: Kinetic Resolution and Enzymatic Coupling. Chembiochem. 2010 Mar 25.
We have previously shown that the beta-aminopeptidases BapA from Sphingosinicella xenopeptidilytica and DmpA from Ochrobactrum anthropi can catalyze reactions with non-natural beta (3)-peptides and beta (3)-amino acid amides. Here we report that these exceptional enzymes are also able to utilize synthetic dipeptides with N-terminal beta (2)-amino acid residues as substrates under aqueous conditions. The suitability of a beta (2)-peptide as a substrate for BapA or DmpA was strongly dependent on the size of the C (alpha) substituent of the N-terminal beta (2)-amino acid. BapA was shown to convert a diastereomeric mixture of the beta (2)-peptide H-beta (2) hPhe-beta (2) hAla-OH, but did not act on diastereomerically pure beta (2),beta (3)-dipeptides containing an N-terminal beta (2)-homoalanine. In contrast, DmpA was only active with the latter dipeptides as substrates. BapA-catalyzed transformation of the diastereomeric mixture of H-beta (2) hPhe-beta (2) hAla-OH proceeded along two highly S-enantioselective reaction routes, one leading to substrate hydrolysis and the other to the synthesis of coupling products. The synthetic route predominated even at neutral pH. A rise in pH of three log units shifted the synthesis-to-hydrolysis ratio (v (S)/v (H)) further towards peptide formation. Because the equilibrium of the reaction lies on the side of hydrolysis, prolonged incubation resulted in the cleavage of all peptides that carried an N-terminal beta-amino acid of S configuration. After completion of the enzymatic reaction, only the S enantiomer of beta (2)-homophenylalanine was detected (ee> 99 % for H-(S)-beta (2)-hPhe-OH, E> 500); this confirmed the high enantioselectivity of the reaction. Our findings suggest interesting new applications of the enzymes BapA and DmpA for the production of enantiopure beta (2)-amino acids and the enantioselective coupling of N-terminal beta (2)-amino acids to peptides. |
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