Association of (+)-catechin and catechin-(4α→ 8)-catechin with oligopeptides
Tsutomu Hatano, Richard W. Hemingway
NOE studies on the complexation of (poly)flavanoids with peptides containing proline residues in aqueous solutions reveal site specific approach directed by hydrophobic interaction of the aromatic rings of catechin and its dimer, catechin-(4CJ. -+ 8)-catechin, to conformationally accessible regions of peptides without strong preference for interaction with proline residues. line and B-ring protons of catechin. Correlations between a hydroxyproline C6 proton (a-oriented proton) to catechin H-6A
... nd H-SA also showed cross peaks. However. presence of strong hydrogen bonding effects was not shown by comparison of IJC chemical shifts. In the presence of catechin. none of the carbons of these amino acids (including carbonyl carbons) shifted from their frequency in spectra recorded in the absence of catechin (changes were within 0.02 ppm). Likewise. none of the catechin carbons (including those bearing a hydroxy group) moved. These results pointed to the importance of hydrophobic interaCtion of the aromatic A and B rings with the aliphatic regions of proline and hydroxyproline. Although polyphenols have been considered to preferentially attack. proline residues in peptides. catechin showed intermolecular NOEs with the other amino acid residues when we used the following dimeric peptides as targets for complexation. Gly-Pro showed two sets of IH and 13C signals. wbich are attributable to the isomers of different configuration at the nitrogen of imino group of proline. The major isomer. with a 2H singlet-like signal for glycine Ca protons. was assigned to the trans-isomer. The minor isomer. with two doublets of the corresponding protons are separated due to the neighbouring proline carbonyl carbon. was assigned to the cis-isomer. For Gly-Pro. the NOESY spectrum showed significant cross peaks between the catechin H-6A and H-SA and the glycine protons. Among them. the cis-isomer showed strong cross peaks whereas the trans-isomer showed only very weak cross peaks with the B-ring protons of catechin.