title: Oxidative coupling of mithramycin and hydroquinone catalyzed by copper oxidases and benzoquinone. Implications for the mechanism of action of aureolic acid antibiotics.
abstract: The copper oxidases human ceruloplasmin and Polyporous anceps laccase catalyze the oxidative coupling of mithramycin (1) and its aglycone chromomycinone (2) with p-hydroquinone to form new mithramycin-hydroquinone (3) and chromomycinone-hydroquinone adducts (4), respectively. Similar adducts could be formed by the nonenzymatic mimic of this reaction using benzoquinone and these aureolic acids in buffer solutions. FABMS of 3 indicated that the hydroquinone moiety was attached to the aureolic acid aglycone. Acid hydrolysis of 3 yielded a compound with the same chromatographic and spectroscopic characteristics as 4. Structure elucidation of 4 by NMR and MS revealed that the hydroquinone was attached to the C-5 position of the aglycone. NMR evidence indicated that 4 consisted of a mixture of ortho-substituted biphenyl rotamers. The mechanism of the copper oxidase catalyzed adduct formation reaction is presumed to involve radical formation through hydrogen removal at the 8-phenolic position, radical isomerization, and coupling with semiquinone radical also formed during enzymatic and nonenzymatic incubations. Identification of the covalent-hydroquinone adduct provides evidence that aureolic acid antibiotics can be metabolically converted to reactive radical intermediates, and it establishes the C-5 position of aureolic acid as an enzymatically reactive site. Unlike mithramycin, the mithramycin-hydroquinone adducts was inactive in the in vivo P388 leukemic antitumor test system.
authors.affiliation: Division of Medicinal and Natural Products Chemistry, University of Iowa, College of Pharmacy, Iowa City 52242.
authors.forename: I O
authors.initials: IO
authors.lastname: Anyanwutaku
authors.forename: R J
authors.initials: RJ
authors.lastname: Petroski
authors.forename: J P
authors.initials: JP
authors.lastname: Rosazza
mesh_terms: D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000138:chemical synthesis* / Q000737:chemistry / Q000627:therapeutic use; D016227:Benzoquinones / Q000737:chemistry*; D002384:Catalysis; D002570:Ceruloplasmin / Q000378:metabolism*; D004353:Drug Evaluation, Preclinical; D006801:Humans; D006873:Hydroquinones / Q000737:chemistry*; D042845:Laccase; D007941:Leukemia P388 / Q000188:drug therapy; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D015394:Molecular Structure; D010088:Oxidoreductases / Q000378:metabolism*; D008926:Plicamycin / Q000031:analogs & derivatives* / Q000737:chemistry* / Q000627:therapeutic use; D011124:Polyporaceae / Q000201:enzymology*; D016339:Spectrometry, Mass, Fast Atom Bombardment
chemical_list: D000903:Antibiotics, Antineoplastic; D016227:Benzoquinones; D006873:Hydroquinones; C004532:quinone; D010088:Oxidoreductases; D042845:Laccase; C024748:copper oxidase; D002570:Ceruloplasmin; D008926:Plicamycin; C031927:hydroquinone