The conformational properties of two pentapeptides Asterin B (△ Pro-Thr-Ser-βPhe-Abu-OMe, 1) and Asterin C (△Pro-Abu-Ser-βPhe- Thr-OMe, 2), isolated from Chinese traditional medicine Aster tataricus, have been investigated by 2D-NMR and restrained molecular dynamic calculations (RMD). The solution conformation of 1 was characterized as a nonclassic β-turnstructure at (△Pro-Thr-Ser-β Phe) region with an amphiphilic feature, which may be related to its antitumor activity against P388 leukemia. There is no evidence in the form of lowered amide proton temperature coefficients for direct hydrogen bonding as a primary source of turn stability. Instead, the major stabilization appears to be the hydrophobic interaction between aromatic rings (△Pro and βPhe). Implications for stabilization of this unusual turn structure during the earliest events in protein folding are discussed. The conformation of 2 in solution was shown to be more flexible with multiple conformational averaging.

Key words: OLIGOPEPTIDE, MOLECULAR DYNAMICS