- Solvolysis of K-region arene oxides: Substituent effects on reactions of benz[a]anthracene 5,6-oxide
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The solvolytic reactivity and products formed from benz[a]anthracene 5,6-oxide (BA-O) on substitution of a methyl group at positions 1 (1-MBA-O), 4 (4-MBA-O), 7 (7-MBA-O), 11 (11-MBA-O), and 12 (12-MBA-O), on 7,12-dimethyl substitution (7,12-DMBA-O), and on 7-bromo substitution in 1:9 dioxane-water and in methanol at 25°C are reported. These substitutions result in > 150-fold differences in their rates of acid-catalyzed solvolysis and cause marked changes in the distribution of solvent adducts and phenols resulting from isomerization. Optically pure BA-O, 7-MBA-O, 12-MBA-O, and 7,12-DMBA-O as well as their optically pure trans dihydrodiols were utilized to determine the point of attack by water in the hydrolysis reactions. In general, the reactions in aqueous dioxane (0.1 M NaClO4) obeyed the rate equation kobsd = kH[H+] + k0, where kH is the second-order rate constant for acid-catalyzed reaction and k0 is the first-order rate constant for spontaneous reaction, to provide biphasic pH-rate profiles. When ionic strength was maintained with 0.5 M KCl, however, more complex pH-rate profiles were observed for some of the arene oxides due to attack of chloride on the neutral epoxide to produce steady-state concentrations of chlorohydrins. Rate enhancement on methyl substitution is largest (kH, ca. 5-fold) when the methyl group is present in the hindered bay region (C1 or C12) or adjacent to the epoxide at C7. The combined effect of two methyl groups (7,12-DMBA-O) is additive (ca. 25-fold). Theoretical calculations (molecular mechanics by PCMODEL-PI and ab initio by GAUSSIAN 86 and 88 programs) of carbocation stability indicate the importance of steric factors in determining relative reactivity and types of products formed from substituted benz[a]anthracene 5,6-oxides.
- Nashed, Nashaat T.,Balani, Suresh K.,Loncharich, Richard J.,Sayer, Jane M.,Shipley, David Y.,Mohan, Ram S.,Whalen, Dale L.,Jerina, Donald M.
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p. 3910 - 3919
(2007/10/02)
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- Synthesis of the Enantiomeric K-Region Arene 5,6-Oxides Derived from Chrysene, 7,12-Dimethylbenzanthracene, and Benzophenanthrene
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K-region arene 5,6-oxides of chrysene, benzophenanthrene Ph>, and 7,12-dimethylbenzanthracene (DMBA) have been synthesized from resolved cis-5,6-dihydrodiols by the ortho ester route as well as from separated bromo(menthyloxy)acetate precursors in the cases of chrysene and BPh.Absolute configurations of the 5,6-oxides and their precursors from chrysene and DMBA have been determined by nucleophilic trans addition of methanol to the oxirane ring and correlation by circular dichroism of the adducts with trans dihydrodiols of known configurations.Confirmation of the configurational assigments to the enantiomeric chrysene cis-5,6-dihydrodiols was achieved by reduction to cis-5,6-dihydroxy-1,2,3,4,5,6-hexahydrochrysene and determination of the skew sense of the resulting biphenyl chromophore through CD measurements.BPh 5,6-oxide enantiomers were assigned by direct comparision with a sample of known configuration on a chiral column.
- Balani, Suresh K.,Bladeren, Peter J. van,Cassidy, E. Sally,Boyd, Derek R.,Jerina, Donald M.
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p. 137 - 144
(2007/10/02)
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- Resolution and Absolute Configuration of K-Region Trans Dihydrodiols from Polycyclic Aromatic Hydrocarbons
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K-region trans dihydrodiols of benzophenanthrene, chrysene, pyrene, and dibenzacridine have been resolved as their diastereomeric diesters with (-)-(menthyloxy)acetic acid, and their absolute configuration have been assigned by the application of circular dichroism and excition chirality methods.For these as well as the K-region trans dihydrodiol derivatives from five other hydrocarbons, a consistent pattern of physical properties has emerged.The R,R diastereomers are less retained on silica gel HPLC columns when eluted with ether-cyclohexane mixtures and show negative values of D in tetrahydrofuran, the degree of magnetic nonequivalence between HA and HB in the -OCHAHBCO2- portion of the diesters (100 MHz, C6D6) is generally much higher for the S,S enantiomers of the dihydrodiols, and the free R,R dihydrodiols have positive values of D in tetrahydrofuran provided their hydroxyl groups do not have a marked preference for the pseudodiaxial conformation.
- Balani, S. K.,Bladeren, P. J. van,Shirai, N.,Jerina, D. M.
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p. 1773 - 1778
(2007/10/02)
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- Direct Enantiomeric Resolution of Some 7,12-Dimethylbenzanthracene Derivatives by High-Performance Liquid Chromatography with Ionically and Covalently bonded Chiral Stationary Phases
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The direct resolution of the enantiomers of trans-3,4-dihydrodiol, trans-5,6-dihydrodiol, cis-5,6-dihydrodiol, trans-8,9-dihydrodiol, and 8,9,10,11-tetrahydro-trans-8,9-diol of 7,12-dimethylbenzanthracene was evaluated by high-pepformance liquid chromatography using commercially available columns packed with (R)-N-(3,5-dinitrobenzoyl)phenylglycine and (S)-N-(3,5-dinitrobenzoyl)leucine either ionically or covalently bonded to γ-aminopropylsilanized silica.The enantiomers of all diol derivatives were resolved by one or more, but not all, of the chiral stationary phases tested.Resolution of enentiomers was confirmed by ultraviolet-visible absorption, mass, and circular dichroism spectral analyses.
- Yang, Shen K.,Weems, Henry B.
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p. 2658 - 2662
(2007/10/02)
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