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.
metachelin, iron-depleted culture conditions, Metarhizium robertsii, fungal siderophore
NCBI PubMed ID: 24992511Publication DOI: 10.1021/np500300sJournal NLM ID: 7906882Publisher: American Society of Pharmacognosy
Correspondence: Krasnoff SB
; Krasnoff SB
Institutions: USDA-ARS-Biological IPM Research Unit, Ithaca, New York, United States, Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York, United States, Department of Plant Pathology and Plant-Microbe Biology, Cornell University, Ithaca, New York, United States
Methods: 13C NMR, 1H NMR, HPLC, ROESY, HR-ESI-MS, antibacterial assay, HMBC, HSQC, optical rotation measurment
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