Synthesis and characterization of enantiomeric anti-2-fluorobenzo[a]pyrene- 7,8-dihydrodiol-9,10-epoxides and their 2′-deoxyguanosine and oligodeoxynucleotide adducts

Benzo[a]pyrene diol epoxides (BPDEs) are the ultimate carcinogenic species of benzo[a]pyrene, a prototype polycyclic aromatic hydrocarbon (PAH). BPDE-modified DNA duplexes can adopt multiple conformations depending on the nature of the modified bases, the stereochemistry at the location of the covalent linkage, and the sequence context surrounding the lesion site. In this paper, we describe the preparation of enantiomeric 2-fluoro-BPDEs, trans-(7R,8S)-dihydroxy-(9S,10R)- and trans-(7S,8R)-(9R,-105)-epoxy-7,8,9,10- tetrtahydro-2-fluorobenzo[a]pyrene (22 and 23, respectively), as models for probing the BPDE-induced conformational heterogeneity. The multistep synthesis of the target diol epoxides described herein entails regiospecific succinoylation of 2-fluoropyrene, followed by a ring closure, regio-and stereospecific construction of the 7,8-dihydrodiol functionality, and a subsequent meta-chloroperbenzoic acid-mediated epoxidation. Stereoselectivity was achieved by using Jacobsen chiral catalysts, which produced greater than ∼90% enantiomeric excess. Absolute configurations at the C7.8 carbons of the FBP derivatives were determined by comparison of the circular dichroism (CD) spectra with those reported for the BP analogues. Analysis of the 3J7.8 vicinal coupling constants, CD shape, and charge density calculations all indicated that the prepared anti-FBPDEs preferentially adopt the pseudo-diequatorial C7.8 diol conformation. Hydrolysis of anti-FBPDEs produced a 9:1 ratio of trans- to cis-opened tetraols. Reactions of each of the anti-FBPDEs with deoxyguanosine 5′-monophosphate produced predominantly trans-anti-N2-dG as the major adducts. Analogous reactions with two 11-mer oligodeoxynucleotides (5′-CCATXGCTACC-3′ where X = dT, dC) gave FBP-modified oligodeoxynucleotides with structures that were characterized by enzyme digest/HPLC and electrospray ionization time-of-flight mass spectrometry data. The oligonucleotide adducts were annealed with the appropriate sequences to form fully complementary duplexes [(5′-CCATXG*CTACC-3′)(5′-GGTAGCYATGG-3′), G* = FBP-N2-dG adduct, X = dT, Y = dA in duplex I; X = dC, Y = dG in duplex II] for CD and UV melting studies. The results of the present study were consistent with those reported previously for BPDE-modified duplexes in the same sequence contexts and support the utility of FBPDEs as useful structural probes. © 2006 American Chemical Society