title: Metachelins, mannosylated and N-oxidized coprogen-type siderophores from Metarhizium robertsii.
abstract: Under iron-depleted culture conditions, the entomopathogenic fungus Metarhizium robertsii (Bischoff, Humber, and Rehner) (= M. anisopliae) produces a complex of extracellular siderophores including novel O-glycosylated and N-oxidized coprogen-type compounds as well as the known fungal siderophores N(α)-dimethylcoprogen (NADC) and dimerumic acid (DA). Metachelin A (1), the most abundant component in the M. robertsii siderophore mixture, was characterized as a 1094 Da analogue of NADC that is O-glycosylated by β-mannose at both terminal hydroxyl groups and N-oxidized at the dimethylated α-nitrogen. The mixture also contained a 1078 Da analogue, metachelin B (2), which lacks the N-oxide modification. Also characterized were the aglycone of 1, i.e., the N-oxide of NADC (3), and the monomannoside of DA (6). N-Oxide and O-glycosyl substituents are unprecedented among microbial siderophores. At high ESIMS source energy and at room temperature in DMSO, 1 underwent Cope elimination, resulting in loss of the N(α)-dimethyl group and dehydration of the α-β bond. High-resolution ESIMS data confirmed that all tri- and dihydroxamate siderophores (1-6) complex with trivalent Fe, Al, and Ga. In a chrome azurol S assay, all of the M. robertsii siderophores showed iron-binding activity roughly equivalent to that of desferrioxamine B.
authors.affiliation: USDA-ARS-Biological IPM Research Unit, Ithaca, New York 14853, United States.
authors.forename: Stuart B
authors.initials: SB
authors.lastname: Krasnoff
authors.forename: Ivan
authors.initials: I
authors.lastname: Keresztes
authors.forename: Bruno G G
authors.initials: BG
authors.lastname: Donzelli
authors.forename: Donna M
authors.initials: DM
authors.lastname: Gibson
mesh_terms: D001692:Biological Transport; D054659:Diketopiperazines / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D005290:Ferric Compounds / Q000737:chemistry / Q000302:isolation & purification* / Q000494:pharmacology; D006877:Hydroxamic Acids / Q000737:chemistry; D062385:Hydroxybenzoates; D007501:Iron / Q000378:metabolism*; D008362:Mannosides / Q000737:chemistry / Q000302:isolation & purification* / Q000494:pharmacology; D052981:Metarhizium / Q000737:chemistry*; D015394:Molecular Structure; D010084:Oxidation-Reduction; D017262:Siderophores / Q000737:chemistry* / Q000494:pharmacology
chemical_list: D054659:Diketopiperazines; D005290:Ferric Compounds; D006877:Hydroxamic Acids; D062385:Hydroxybenzoates; D008362:Mannosides; D017262:Siderophores; C552122:dimerumic acid; C000591563:metachelin A; C065863:N(alpha)-dimethylcoprogen; C015076:chrome azurol S; C010896:coprogen; D007501:Iron