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A protein-cleaving catalyst specific for a disease-related protein can be used as a catalytic drug. As the first protein-cleaving catalyst selective for a protein substrate, a catalyst for myoglobin was designed by attaching Cu(II) or Co(III) complex of cyclen to a binding site searched by a combinatorial method using peptide nucleic acid monomers as building units. [reaction: see text]

A novel methodology is reported for construction of active sites of artificial multinuclear metalloenzymes:  transfer of metal-chelating sites confined in a prebuilt cage to a polymeric backbone. Artificial active sites comprising two or three moieties of Cu(II) complex of tris(2-aminoethyl)amine (tren) were prepared by transfer of Cu(II)tren units confined in a molecular bowl (MB) to poly(chloromethylstyrene-co-divinylbenzene) (PCD). By treatment of unreacted chloro groups of the resulting PCD with methoxide and destruction of the MB moieties attached to PCD with acid followed by addition of Cu(II) ion to the exposed tren moieties, catalytic polymers with peptidase activity were obtained. The average number (β) of proximal Cu(II)tren moieties in the active site of the artificial multinuclear metallopeptidase was determined by quantifying the Cu(II) content. Several species of the artificial metallopeptidases with different β contents were prepared and examined for catalytic activity in hydrolysis of various cinnamoyl amide derivatives. The PCD-based catalytic polymers did not hydrolyze a neutral amide but effectively hydrolyzed carboxyl-containing amides (N-cinnamoyl glycine, N-cinnamoyl β-alanine, and N-cinnamoyl γ-amino butyrate). Analysis of the kinetic data revealed that the active sites comprising three Cu(II)tren units were mainly responsible for the catalytic activity. When analyzed in terms of k cat, the catalytic activity of the PCD-based artificial peptidase was comparable to or better than the catalytic antibody with the highest peptidase activity reported to date. A mechanism is suggested for the effective cooperation among the three metal centers of the active site in hydrolysis of the carboxyl-containing amides.

To provide a firm basis for the new paradigm of drug discovery based on peptide-cleaving catalysts, oligopeptide-cleaving catalysts were searched for by using human angiotensin I (Ang-I) and angiotensin II (Ang-II) as the substrates. Catalyst candidates containing the Co(III) complex of cyclen as the catalytic center were prepared by multicomponent condensation reactions. From two types of chemical libraries containing about 3,600 catalyst candidates, two compounds [SS-Co(III)X and S-Co(III)Y] were selected as the most active catalysts. On incubation with SS-Co(III)X and S-Co(III)Y, both Ang-I and Ang-II were cleaved by oxidative decarboxylation instead of peptide hydrolysis: the N-terminal Asp residues of Ang-I and Ang-II were converted to pyruvate residues. Catalysts for oxidative decarboxylation of the N-terminal Asp residue contained in an oligopeptide are unprecedented in both biological and chemical systems. Detailed kinetics analysis suggested that Ang-I and Ang-II can be cleaved with half-lives much less than 1 h if the structures of the chelating ligands of the catalysts are further improved. The results indicated that the concept of the peptide-cleaving catalysts can be expanded to include oligopeptides as the targets and nonhydrolytic reactions as the means for cleavage.

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