Crystal and molecular structure of the centrosymmetric meso-valinomycin analogue—cyclo (D-Val-D-Hyi-D-Val-L-Hyi-L-Val-D-Hyi-L-Val-L-Hyi-L-Val-D-Hyi-L-Val-L-Hyi) (C60H102N6O18)

The crystal structure of cyclo (D -Val-D -Hyi-D -Val-L -Hyi-L -Val-D -Hyi-L -Val-L -Hyi-L -Val-D -Hyi-L -Val-L -Hyi)-2H₂O has been solved by x-ray direct methods. The crystals (grown from a mixture of octane / CH₂C₁₂) are an orthorhombic, centrosymmetric space group Pbca, cell parameters a = 11.458(2). b = 25.613(3). c = 23.691(3) Å. Z = 4; therefore the molecule lies on a center of inversion in the cell. The atomic coordinates for the C, N, and O atoms were refined in the anisotropic thermal motion approximation (allowing for II-atom contribution to F_cal) to a standard R- factor value of 0.081. In contrast to meso-valinomycin, the analogue under study does not adopt an octahedral cage bracelet conformation. It has an unusual centrosymmetric elongated form with two type II terminal β-bends formed by N? H?C?O 4 → 1 type intramolecular H bonds. Two symmetry-related water molecules reside in the elongated molecular cavity of the centrosymmetric depsipeptide ring. © 1995 John Wiley & Sons, Inc.