Conformation of cyclic heptapeptides: Solid and solution state conformation of yunnanin A

The solid and solution state conformation of yunnanin A, a cyclic heptapeptide, cyclo(-Gly-Tyr-Gly-Gly-Pro-Phe-Pro-),: isolated from the roots of Stellaria yunnanensis were studied. The X-ray diffraction studies showed that the crystal of yunnanin A [orthorhombic form from a ethanol-methanol mixture, a=11.754 (to), b=12.576 (7), c=30.731 (6) Angstrom, space group P222(1), z=4] had three intramolecular hydrogen bonds forming one type II, one type II' beta-turns, and a classical beta-bulge unit with all trans amide bonds. The dominant solution conformation analyzed by NMR spectroscopy, Monte Carlo (MC) and restrained molecular dynamics (MD) calculations implemented in MacroModel/Batchmin (Ver. 4.5) was homologous to that in the solid state. (C) 1997, Elsevier Science Ltd.