Abstract
Conformational analysis of an antitumour cyclic pentapeptide, astin B, isolated from Aster tataricus, was conducted by 2D-NMR techniques, temperature effects on NH protons, rate of hydrogen-deuterium exchange, vicinal NH-CαH coupling constants, and NOE experiments. The methods of molecular mechanics and restrained molecular dynamics calculations were applied to understand the energetic preferences of various conformations of astin B. Distances involving in three intramolecular hydrogen bonds and the NOE correlations were used for the refinements AMBER program. These results indicated that the conformation in the solution state was, on the whole, homologous to that observed in the solid state. Conformational difference between astin B, showing a cis configuration in a proline amide bond, and cyclochlorotine from Penicillium islandicum, showing all trans amide configurations, was also discussed.
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