CHIROPTICAL PROPERTIES OF AROMATIC RESIDUES IN CYCLOLINOPEPTIDE-A ANDITS ANALOGS

It was found that cyclolinopeptide A [c-Leu-Ile-Ile-Leu-Val-Pro-Pro-Ph e-Phe), CLA] is a very suitable model for studying the spectroscopic p roperties of aromatic side chains. To investigate these properties the H-1-NMR and CD spectra of the CLA analogues, where tyrosine was subst ituted for one or both phenylalanines, and the CD spectra of similarly substituted tryptophan and alanine analogues of CLA, were measured. T he NMR studies show a distinct differentiation in the chemical shifts of aromatic protons, which could be attributed to the edge-to-face int eraction of the rings. The optical activity of the aromatic side chain s depends on their position in the peptide chain and corresponds to th e differences in the side chain conformation of both aromatic residues .