Structure of ferrichrome-type siderophores with dissimilarN ^δ-acyl groups: Asperchrome B₁,B₂,₃,D₁, D₂ and D₃

Summary

Asperchromes are a series of iron-chelating compounds which contain a cyclic hexapeptide backbone as in ferrichrome siderophores and differ from the latter in having heterogenous acyl groups in the ornithine side chains. The molecular structures of the asperchrome B and D series have been determined by¹H- and¹³C-NMR spectroscopy; single-crystal X-ray diffraction was used to determine the detailed structural features of asperchrome B₁ and asperchrome D₁. Asperchrome B₁ crystallizes in the triclinic space group P1 witha= 1.3143(5) nm,b=1.2200(5) nm,c=0.8949(3) nm,α=105.17(4)°,β=94.03(3)°, γ=109.65(3)°,V=1.2843 nm³,Z=1, ρ _x =1.446 g cm⁻³. FinalR=0.054 for 4625 reflections measured at 138 K using MoKα. Asperchrome D₁ crystallizes in the monoclinic space group P2₁ witha=1.2248(11) nm,b=1.3795(9) nm,c=1.3644(6) nm,β=93.24(6)°,V=2.3016 nm³,Z=2, ρ _x =1.418 g cm⁻³. FinalR=0.110 for 3180 reflections measured at 138 K using MoKα radiation. The conformation of the molecular backbone and iron coordination geometry in both asperchrome B₁ and D₁ compare well with those observed in other known ferrichrome siderophores. The differences in the acyl groups are illustrated and the structural results are correlated with their iron transport properties.