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The synthesis of 4,5-dihydro-4,5-dioxo-l/f-pyrrolo[2,3-/]quinoline-2-carboxylic acid (7,9-didecarboxymethoxatin, 70X) and its ester (60X) are described and their acid-base properties, electrochemistry, and chemical properties are compared to the cofactor Methoxatin, as well as to those of other o-quinones. The two-electron redox potentials of 60x and 70x are shown to be ca. 110 mV less than those of the penanthroline-5,6-quinones but to be comparable to those of methoxatin at all pH values. Replacement of the pyridine ring of 70X by a benzene ring reduces its oxidation potential by 100 mV. 70x forms a C-5 adduct with acetone and a cyclic bis(carbinolamine) adduct with urea. The rate constants for formation and dissociation of the urea adducts of methoxatin, 60X, and the most electrophilic phenanthrolinequinone (30x) are compared. The o-quinone

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The possibility that the spectrum of intermediate two, seen in the course of reaction of flavoenzyme phenol hydroxylases, may be attributable to iminol isomers of a flavin-derived 6-arylamino-5-oxo(3H,5H)uracil (flavin mixed-function oxidase/hydroxylation) ALBERT WESSIAK, J. BARRY NOAR, AND THOMAS C. BRUICE* Department of Chemistry, University of California, Santa Barbara, CA 93106 Contributed by Thomas C. Bruice, September 19, 1983 ABSTRACT A commonly held view of the mechanism of flavin mixed-function oxidases is that enzyme-bound 4a-hydroperoxyflavin (4a-FIHOOH) undergoes ring opening to provide a carbonyl oxide (IV), which, after transferring an oxene equivalent to substrate, yields a 6-arylamino-5-oxo(3H,5H)-uracil (I). The latter is then thought to undergo ring closure to form a 4a-hydroxyflavin (4a-FIHOH), which by loss of water yields flavin (scheme I). A close structural analogue of I (i.e., III) has been synthesized. Comparison of the spectra of III (and II), taken in solvents of widely differing dielectric constants and in a strongly basic medium, with those of the intermediate(s) observed to be formed in time between 4a-FIHOOH and 4a-FIHOH has shown that the enzyme-bound intermediate(s) does not resemble spectrally I nor its iminol tautomers.

N -Nitrosodibenzylamine has been oxidised to benzaldehyde and benzyl alcohol by iodosylbenzene, 3c h loroperoxybenzoic acid and tbu tyl h yd roperoxide ca tal ysed by tetrap hen yl porp hyri na toi ron (11 I) chloride or -manganese(iii) chloride. The influence of reaction conditions on the product yields and distribution have been studied. Kinetic isotope effects have been measured with deuteriated N-nitrosodibenzylamines for inter-and intra-molecular competition for the oxidants. The evidence presented is in favour of the iodosylbenzene and t-butyl hydroperoxide oxidations being initiated by hydrogen-atom abstraction by the oxidant from the x-hydrogen of the benzyl group. However, oxidations by the peroxy acid systems may proceed by an initial electron transfer. The reactions of N-nitrosodimethylamine and N-nitrosopiperidine with the metalloporphyrin-catalysed systems show that these substrates are surprisingly unreactive towards oxidation.