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A large number of iron-chelating compounds (siderophores) were isolated from supernatants of irondeficient cultures of a mold isolate, subsequently identified as Aspergillus ochraceous. Siderophores in their iron chelate form were purified to homogeneity by using Bio-Gel P2, silica gel, and C-18 bonded silica gel (reverse-phase) columns. Most of these compounds, as identified by 'H and 13C nuclear magnetic resonance spectroscopy and X-ray crystallography, belong to the ferrichrome family. The organism produces ferrirubin and ferrichrysin as the predominant and the second major compound (62 and 15% of the total siderophores), respectively. Ferrichrysin appears as the first siderophore in the medium on day 2 of growth. Several of the other siderophores are novel and ranged in quantities from 0.2 to 5% of the total. The trivial names asperchrome A, Bi, B2, C, DI, D2, and D3 are proposed for these novel compounds, which are all members of the ferrichrome family, and all but the first one contain a common Orn,-Orn2-Orn3-Ser1-Ser2-Gly cyclic hexapeptide ring with three dissimilar ornithyl 8-N-acyl groups. Another compound which appeared late in the growth period was similar to fusarinine C (fusigen). All of these compounds showed growth factor activity to various extents in bioassays with Arthrobacter flavescens Jg-9. None of these compounds showed antibacterial activity against Escherichia coli or Bacillus megaterium.

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. The hydroxamate group in each compound assumes the trans conformation as observed in other secondary hydroxamic acids. The interchange of the C and N substituents influences the planarity and dimensions (C---~O, C--N bonds) of the hydroxa, mate moiety. In MTH the hydroxamate group shows significant deviation from planarity; the r.m.s, deviation of the four atoms, @--N--O(H), is 0.094 A, whereas in MPA it is only 0.004A. This nonplanarity is due largely to out-of-plane bending at N, XN = 23"9 (1) °, as compared to XN = 0"1 ° for MPA. The phenyl ring in MPA is nearly coplanar with the hydroxamate plane (dihedral angle of 10.3°), but is significantly rotated from the hydroxamate plane in MTH (dihedral angle of 43.8°). Electronic differences in the two molecules are considered.