Structure and molecular mechanics of ferrirhodin

C41H64FeN9O17.7 1/2H2O, Mr = 1146.0, orthorhombic, P2(1)2(1)2(1), a = 9.740 (7), b = 16.764 (10), c = 32.632 (17) A, V = 5328 (6) A3, Z = 4, D chi = 1.43 g cm-3, Mo K alpha, lambda = 0.71069 A, mu = 3.26 cm-1, F(000) = 2428, T = 138 (2) K, R = 0.0986 for 3543 observed reflections. Ferrirhodin, a ferrichrome siderophore (iron transport agent) was isolated from low-iron cultures of Aspergillus versicolor and A. nidulans. The compound is isomeric with another microbial siderophore, ferrirubin, but is different in having cis, rather than trans, anhydromevalonic acid as acyl groups. The conformation of the molecular backbone and iron coordination geometry compares well with ferrirubin and other ferrichrome structures. The differences between the acyl groups of ferrirubin and ferrirhodin are explored using molecular-mechanics modeling.