Iron uptake system of some members of the genus tolypocladium: crystal structure of the ligand and its iron(III) complex

Abstract

A new type of fungal hydroxamic acid (1′S,2′R,4′S,6′R)-3-(2′,4′-dimethyl-6′-vinylcyclohexyl)-1,4-dihydroxy-2(1H)-pyridone (tolypocin, HL) has been isolated from the mycelium of the fungus Tolypocladium geodes. The acid (C₁₅H₂₁NO₃) crystallized from methanol [monoclinic, space group P2₁, Z= 4, a= 12.28(1), b= 9.958(5), c= 12.737(4), Å, β= 94.91(5)°]. The structure was solved by direct methods and refined to a final R value of 0.055 for 2393 unique observed reflections. The iron(III) trischelate complex of this ligand [FeL₃] has been isolated from the mycelium of the fungus Tolypocladium terricola. Its methanol solvate (C₄₅H₆₀FeN₃O₉·2MeOH) was crystallized from methanol [orthorhombic, space group P2₁2₁2₁, Z= 4, a= 20.27(3), b= 19.35(5), c= 13.43(4)Å]. The structure was solved by direct methods and refined to a final R value of 0.062 for 5562 observed reflections. The absolute configuration of the complex as determined from CD spectra and anomalous X-ray dispersion has been shown to be Λ-cis both in solution and in the solid state.