The reactions of chromomycinone and derivatives

Oxidative coupling of mithramycin and hydroquinone catalyzed by copper oxidases and benzoquinone. Implications for the mechanism of action of aureolic acid antibiotics

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.

Interaction between enzyme-generated triplet carbonyls and molecules intercalated into DNA

The phosphorescence from enzyme-generated and -protected triplet acetone is very efficiently quenched by dyes intercalated into DNA. The process is unlikely to be due to energy transfer and is tentatively ascribed to electron transfer occurring within the DNA helix complex with the acting enzyme. This quenching markedly protects DNA from breaks induced by triplet acetone. In the case of some barely emissive enzyme-generated triplet carbonyl species, it is possible to detect a weak emission resulting from the interaction with dye X DNA; this emission may be associated with back electron transfer.