Cyclic enediyne-amino acid chimeras as new aminopeptidase N inhibitors

Enediyne-peptide conjugates were designed with the aim to inhibit aminopeptidase N, a widespread ectoenzyme with a variety of functions, like protein digestion, inactivation of cytokines in the immune system and endogenous opioid peptides in the central nervous system. Enediyne moiety was embedded within the 12-membered ring with hydrophobic amino acid alanine, valine, leucine or phenylalanine used as carriers. Aromatic part of the enediyne bridging unit and the amino acid side chains were considered as pharmacophores for the binding to the aminopeptidase N (APN) active site. Additionally, the fused enediyne-amino acid "heads" were bound through a flexible linker to the L-lysine, an amino group donor. The synthesis included building the aromatic enediyne core at the C-terminal of amino acids and subsequent intramolecular N-alkylation. APN inhibition test revealed that the alanine-based derivative 9a inhibits the APN with IC(50) of 34 ± 11 μM. Enediyne-alanine conjugate 12 missing the flexible linker was much less effective in the APN inhibition. These results show that enediyne-fused amino acids have potential as new pharmacophores in the design of APN inhibitors.