Synthesis and evaluation of the biological activity of analogues of pepstatin

Abstract

Synthesis of all four stereoisomers of the novel amino acid statine, 4-amino-3-hydroxy-6-methylhepatanoic acid, and alastatine, 4-amino-3-hydroxypentanoic acid has been accomplished. Several tripeptide analogues of pepstatin have been prepared and tested as inhibitors of pepsin and cathepsin D in vitro. N-Carbobenzoxy-L-valyl-L-valyl-(3S,4S)-statine, 22a, was 20-fold less effective than pepstatin. The analogue of 22a in which the (3S,4S)-statine was replaced by (3R,4S)-statine showed a 210-fold decrease in activity, whereas the replacement of (3S,4R)-statine resulted in 2240-fold decrease. These results indicate that the stereochemistry of statine is important for the biological activity of the peptides. The S-configuration at both the 3 and 4 positions is required for tight binding to the enzyme. The antipepsin activity of the tripeptide containing (3S,4S)-alastatine was 168 times weaker than that of tripeptide 22a, while as a cathepsin D inhibitor the former tripeptide was 875 times less effective than the latter tripeptide. These data suggest that the side chain of the novel amino acid plays a significant role in the biological action of the peptide inhibitors.