The crystal and molecular structure of a valinomycin analogue cyclo[(o-Val-L-LacL-Ala-D-Hyi)2(D-Val-L-Lac-LVal-D-Hyi)]-H₂O (C₅₀H₈₂N₆O₁₈-H₂O)

The crystal and molecular structure of the valinomycin analogue, cyclo[( D-Val-LLac-L-AIa-D-Hyi)z(D-Val-L-Lac-L-Val-D-Hyi)] has been solved by x-ray direct methods using the "Shake and Bake" procedure. The crystals, grown from a mixture of octane/CH2Cl2, belong to space group P2; (Z = 4) with cell parameters a = 70.29, b = 32.08, c = 18.73 A, = 97.05", and contain two molecules per asymmetric unit. After anisotropic refinement the standard reliability factor was Rl = 0.058. The conformations of both independent molecules is similar to that observed for isoleucinomycin, cyclo[-(D-Ile-L-Lac-L-Ile-D-Hyi)3] [V. Z. Pletnev et al. (1980) Biopolymers, Vol. 19, pp. 1517-1534]. The structure has an asymmetric conformation stabilized by six intramolecular H bonds, five bonds being of the 4 -> / type and one bond being of the 5 -1 type. One water molecule is caged in the internal cavity of each cyclodepsipeptide. This conformation could represent an intermediate state behveen free and complexed forms of valinomycin.