Structure of Phenolic Isomers of 2- and 3-Nitrofluoranthene Studied by One- and Two-Dimensional 1H NMR Spectroscopy. Comparative Analysis of Mutagenicity

The structures of selected phenolic metabolites of 2- and 3-nitrofluoranthene have been analyzed. 1H NMR spectral analysis at 500 MHz using one- and two-dimensional methods proves that the site of hydroxy substitution in two metabolites previously reported as 3-nitrofluoranthen-8-ol and 3-nitrofluoranthen-9-ol had been reversed. A third and previously unidentified metabolite is shown to be 3-nitrofluoranthen-7-ol. Complete analysis of NMR spectral data on 2- and 3-nitrofluoranthene enabled confirmation of the previously reported structures of 2-nitrofluoranthen-8-ol and 2-nitrofluoranthen-9-ol from derived chemical shift substituent effects. Chemical shift data suggest that the nitro group is not strictly coplanar with the aromatic ring system in solution and that metabolism at a distant site can alter the conformation about the C-N bond of the nitro group. Reported mutagenicity data are analyzed relative to imine quinone formation, chemical shift substituent effects, electronegativity effects, and conformation in an attempt to explain the large differences in mutagenicity between the C8 and C9 hydroxy isomers of 2- and 3-nitrofluoranthene.