Crystal and molecular structure of Destruxin B.

The cyclic hexadepsipeptide mycotoxin Destruxin B, produced by Metarrhizium anisopliae, crystallizes in the orthorhombic space group P212121, with a = 11.010(2)A, b = 14.679(5)A, c = 21.273(7)A and Z = 4. The structure was solved by direct methods and refined by least-squares technique to a final unweighted R value of 0.051, for 3361 reflections with I greater than 3 sigma (I). The backbone of the peptide is asymmetric and is made of 5 trans peptide and ester units and 1 cis peptide unit. The backbone conformation of this cyclic depsipeptide is very similar to that of Roseotoxin B, an analogous mycotoxin produced by Trichothecium roseum. The conformation in the crystalline state also correlates well with the solution conformation, as reported from proton n.m.r. studies. The crystal packing is directed by van der Waals contacts.