Fjord-region Benzo[g]chrysene-11,12-dihydrodiol and Benzo[c]phenanthrene-3,4-dihydrodiol as Substrates for Rat Liver Dihydrodiol Dehydrogenase (AKR1C9): Structural Basis for Stereochemical Preference

Abstract

This study demonstrates that benzo[g]chrysene-11,12-dihydrodiol (B[g]C-11,12-dihydrodiol) derived from the fjord-region parent hydrocarbon B[g]C is oxidized by rat AKR1C9 with a k cat / K m 100 times greater than that observed with the commonly studied bay-region benzo -11,12dihydrodiol were purified by chiral RP-HPLC. The 11S,12S-stereoisomer was oxidized at the same rate as the racemate. The 11R,12R-stereoisomer did not act as an inhibitor to AKR1C9, indicating that the (-)-R,R-stereoisomer was excluded from the active site. To understand the basis of stereochemical preference, we screened alanine-scanning mutants of active site residues of AKR1C9. These studies revealed that in comparison to the wild type, F129A, W227A, and Y310A enabled the oxidation of both the B[g]C-11S,12S-dihydrodiol and the B[g]C-11R,12R-dihydrodiol. Molecular modeling revealed that unlike B[a]P-7,8-dihydrodiol and B[c]Ph-3,4-dihydrodiol, B[g]C-11,12-dihydrodiol enantiomers are significantly bent out of plane. As a consequence, the (-)-R,R-stereoisomer was prevented from binding to the active site because of unfavorable interactions with F129, W227, or Y310. Additionally, LC/MS validated that the product of the reaction of B[g]C-11,12-dihydrodiol oxidation catalyzed by AKR1C9 was B[g] C-11,12-dione, which was trapped in vitro with the nucleophile 2-mercaptoethanol. The similarity between rates of trans-dihydrodiol oxidation by the rat and human liver specific AKRs (AKR1C9 and AKR1C4) implicate these enzymes in hepatocarcinogenesis in rats observed with the fjordregion PAH.

Structure Control of Polysaccharide Derivatives for Efficient Separation of Enantiomers by Chromatography

“…According to these statistics, the 3,5-dimethylphenylcarbamates of cellulose, 17ab (Chiralcel OD), and amylose, 18ab (Chiralpak AD), seem to be the most popular ones, followed by cellulose 4-methylbenzoate, 13b (Chiralcel OJ), and amylose ( S )-1-phenylethylcarbamate, ( S )- 30a (Chiralpak AS). Figure shows the recent examples of chiral compounds resolved by the polysaccharide-based CSPs, which include alcohols, amines, , carboxylic acids, ethers, carbonyl and cyano compounds, aromatic hydrocarbons, , nonaromatic compounds, metal-containing compounds, − chiral sulfur or phosphorus , compounds, and axially, − planar, and topologically − asymmetric compounds. For more examples of the available chiral compounds, see the reviews ,− and catalogs. , …”

The Role of Human Aldo-Keto Reductases in the Metabolic Activation and Detoxication of Polycyclic Aromatic Hydrocarbons: Interconversion of PAH Catechols and PAH o-Quinones

“…The substrate specificity of AKRs covers structurally diverse PAH trans -dihydrodiols which range from the simplest trans -1,2-dihydroxy-1,2-dihydro-naphthalene, to bay-region dihydrodiols (e.g., trans -1,2-dihydroxy-1,2-dihydrochrysene), to methylated bay-region dihydrodiols (e.g., trans -3,4-dihydroxy-3,4-dihydro-7-methylbenz[ a ]anthracene), and to fjord -region dihydrodiols (e.g., trans -11,12-dihydroxy-11,12-dihydrobenzo[ g ]chrysene). In contrast, K- region dihydrodiols, in which the dihydroxy groups are located on a central benzo-ring, (e.g., trans -9,10-dihydroxy-9,10-dihydrophenanthrene and trans -4,5-dihydroxy-4,5-dihydroB[ a ]P) are not substrates of AKRs (Table 1 ; Palackal et al, 2001 , 2002 ; Shultz et al, 2008 ).…”