Structure of the cyclohexapeptide cleromyrine II trihydrate.

C29H40N6O7.3H2O, Mr = 638.7, trigonal, P3(1)21, a = 14.190 (2), c = 29.833 (4) A, V = 5202 (1) A3, Z = 6, Dx = 1.22 g cm-3, Cu K alpha, lambda = 1.54178 A, mu = 7.8 cm-1, F(000) = 2052, T = 291 K, R = 0.069 for 1942 observed reflections. The new cyclohexapeptide cleromyrine II was isolated from Clerodendrum myricoides. Its structure was established by spectroscopic and X-ray diffraction methods as cyclo(-Gly-Tyr-Gly-Pro-Leu-Pro-). The conformation essentially consists of two beta-turns including the Pro residues and one central very short antiparallel beta-sheet stabilized by two intramolecular hydrogen bonds: N(Tyr2)...O(Leu5) = 2.94 (2) A and N(Leu5)...O(Tyr2) = 3.02 (2) A.