CONFORMATIONAL-ANALYSIS OF A CYCLIC HEXAPEPTIDE, SEGETALIN-A FROM VACCARIA-SEGETALIS

To establish a pharmacophore model, conformation in solid and solution states of a cyclic hexapeptide, segetalin A, having an estrogen-like activity, was investigated by a combination of X-ray analysis, high fi eld NMR and computational chemical evidence. The three-dimensional str ucture of crystalline segetalin A was characterized by two beta-turn s tructures, one being of type I and the other of type VI, fixed by the two trans-annular hydrogen bonds formed between the 1st Gly and the 4t h Val. On the other hand, in solution, the molecule was shown to have two B-turn structures, one being of type II and the other of type VI, by NMR and MD calculation, demonstrating that segetalin A takes differ ent backbone conformations in solid and solution states.