Preparation of optically pure anti-diolepoxides of 2-fluorobenzo[a]-pyrene and their DNA adducts
Benzo[a]pyrene (BP) is a prototypical PAH and undergoes metabolic activation in vivo to highly mutagenic/carcinogenic diol epoxide derivatives (BPDE) that bind to DNA, ultimately initiating sequence-specific mutations. Structural studies indicate that BPDE-modified DNA exist in three major conformations: base-displacement, minor-groove, and classical intercalation. The relative conformeric ratios of these structures are known to vary depending on the modified base and the base sequences surrounding the lesion site. Our long-term research goal is to investigate the sequence dependent conformational heterogeneity of BP-DNA adducts with 19F NMR technique, which then requires preparation of (+)-and (−)-anti-2-fluorobenzo[a]pyrene diol epoxides (2-FBPDE) as 19F NMR probes. Enantioselective preparation of the title compounds was accomplished via an 18-step total synthetic procedure. All of the synthetic intermediates have been characterized by analyses of 1H NMR, 13C NMR, MS and elemental analyses. The enantiomeric excess of the initial epoxide chiral intermediates was measured to be higher than 90% by HPLC/(−)-menthoxyacetyl chloride methods. 1H NMR studies show that both anti-2-FBPDE and anti-BPDE exhibit the 7,8-pseudo-diequatorial dihydrodiol conformation, indicating the minimal influence of the 2-fluorine atom. Reaction of anti-2-FBPDE with dGMP gave the monomeric anti-2-FBPDE-N 2-dG adduct. Two oligonucleotides sequences: 5′-CCATCGCTACC-3 ′ and 5′-CCATTGCTACC-3′ have been used in binding with anti-2FBPDE. The corresponding oligo adducts were isolated by HPLC, and digested to individual nucleosides with enzymes. Comparison of HPLC profiles showed that the enzyme-digested covalent (+)-trans-adduct co-eluted with the authentic (+)-2-FBPDE-dG adduct, confirming the adduct formation with the sole dG in the sequences. The adducted oligonucleotides were annealed with their complementary sequences to form the corresponding duplexes and used for CD, thermodynamic and UV melting studies, and the results were compared with those obtained from the nonfluorinated BPDE. The structural and physicochemical similarities between BPDE and 2-FBPDE suggest that anti-2-FBPDE could be used as good 19F NMR probes for future conformational studies of BPDE-DNA adducts with or without the presence of enzymes and other associative proteins. ^
"Preparation of optically pure anti-diolepoxides of 2-fluorobenzo[a]-pyrene and their DNA adducts"
Dissertations and Master's Theses (Campus Access).