Enzyme-inhibitory conformation of dipeptides containing sterically constrained amino acid 2,3-methanophenylalanine

Dipeptides containing 2,3-methanophenylalanine, a sterically constrained amino acid with alpha,beta-cyclopropane ring, showed fairly strong inhibitory activity for the hydrolysis of Ac-L-Tyr-OEt by chymotrypsin. Kinetic analyses of the inhibition by dipeptides, H-inverted delta E Phe-Leu (or Phe)-OMe (or OH), indicated the mode of inhibition to be competitive. Comparative analyses of the inhibitory constants Ki have clarified several structural elements necessary to elicit an inhibitory activity. Those include the (2R,3S)-configuration of the inverted delta E Phe residue, the phenyl side chain at position 2 and the C-terminal methylesterification. These structural conditions suggested that the peptides are in specific inhibitory conformation. In the conformational analyses of these dipeptide inhibitors by a high resolution 1H-NMR (270 MHz), the measurement of enhancements of the nuclear Overhauser effect indicated that an intramolecular hydrophobic bonding exists between the inverted delta Phe-phenyl and ester-methyl to construct the hydrophobic core in the molecule. It was suggested that this hydrophobic core interacts with the chymotrypsin S2 site and prevents the hydrolysis of methyl ester. The Leu2 or Phe2 interacts with the enzyme S1 site. The structure of dipeptides containing 2,3-methanophenylalanine has been characterized as an enzyme-inhibitory conformation that interacts with the enzyme at its catalytic center.