3-Aminopyrazole derivatives are the first artificial templates that stabilize the β-sheet conformation in N/C-protected dipeptides by purely intermolecular interactions. In the complex two aminopyrazole molecules lie exactly above and below the peptide backbone. Binding to the top face of the peptide is strongly favored because it forms three cooperative hydrogen bonds simultaneously to the receptor molecule, whereas the bottom face has only two. Polymerizable 3-amino- and 3-amidopyrazoles have been made accessible in excellent yields by a general route starting from p-toluic acid. With 1H NMR titrations binding constants for the 1:1 complex of up to 880 M-1 have been determined in chloroform. The association constants are strongly influenced by the electronic character of the aminopyrazole derivative as well as by the steric demand of the peptide residues. Variable temperature studies prove that the complex is formed by dynamic hydrogen bonds and confirmed the preferential binding of the receptor molecules at the top face. By detailed Karplus-analysis of the NH-α-CH coupling constants in the complex a remarkable correlation between the dihedral angle θ and the degree of complexation was found, which shows that several amidopyrazoles are capable of forcing the dipeptide into an almost ideal β-sheet conformation. In glycine-containing dipeptides the third hydrogen bond slows down the free rotation around the C−C/C−N bond to almost zero. Intramolecular nuclear Overhauser enhancements (NOE) provide additional evidence for the peptide's extended conformation, while strong reciprocal intermolecular NOEs give the final proof of the existence of the critical third hydrogen bond and the postulated mutual orientation of the complexation partners. First 1H NMR titrations with tripeptides show very promising results concerning the application of this concept to oligopeptides.

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