Synthesis and Characterization of Enantiomeric anti-2-Fluorobenzo[a]pyrene-7,8-dihydrodiol-9,10-epoxides and Their 2‘-Deoxyguanosine and Oligodeoxynucleotide Adducts

Abstract

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,10S)-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 approximately 90% enantiomeric excess. Absolute configurations at the C(7,8) 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 3J(7,8) vicinal coupling constants, CD shape, and charge density calculations all indicated that the prepared anti-FBPDEs preferentially adopt the pseudo-diequatorial C(7,8) 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'-CCATXGCTACC-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.

Synthesis of Oligonucleotides Containing the N2-Deoxyguanosine Adduct of the Dietary Carcinogen 2-Amino-3-methylimidazo[4,5-f]quinoline

“…While there is a wide range of T m values for the dGuo-N 2 -PAH adducts, they typically destabilize the duplex by 5-12 °C as compared to unmodified (69)(70)(71)(72)(73). The (−)-and (+)-dGuo-syn-BPDE adducts have been reported to lower the T m of the duplex 5′-CCTATAGATATCC-3′ by 15.5 and 19°C relative to unmodified (72).…”

Synthesis of substituted pyrenes by indirect methods

“…45,46 Currently there are several methods reported for the preparative synthesis of THPy using H 2 /Pd/C in EtOAc (Table 1). [47][48][49][50][51][52][53][54] Some authors have reported that hydrogenation does not take place unless the commercial pyrene starting material is purified by column chromatography 47 or desulphurisation with RANEY® nickel 50,53,54 prior to the reaction. The latter method introduces traces of water (ca.…”

“…Common steps to increase the extent of reaction are addition of a very large amount of catalyst 48,54 and performing several hydrogenation cycles with fresh catalyst. 49,51 More recently, higher pressures and temperatures have been applied, reducing reaction times and the amounts of impurities found in the crude products. 52,53 In general, the main impurity is 1,2,3,6,7,8-hexahydropyrene (HHPy) 13, which can be removed by column chromatography on Florisil, 47 silica 49,51,54 or alumina, 53 or by diacetylation of the crude product followed by fractional precipitation of the impurity.…”

“…58 This reaction has also been performed on the aromatised analogue 2-aminopyrene 16 under Balz-Schiemann conditions using t-BuONO and Et 2 O•BF 3 . 51 A number of deuterated pyrenes were made via treatment of THPy 12 with P 2 O 5 in D 2 O to give 66. Aromatisation-bromination-reduction then gave dideuteropyrene 67, while bromination-reductionaromatisation gave tetradeuteriopyrene 68.…”

Biosynthesis of chiral methyl ketone cyanohydrins catalyzed by oxynitrilase in Chaenomeles speciosa seed meal

“…Research on the stereoselectivity, as well as on the relationships between the substrates and the enzyme on the oxynitrilase in Chaenomeles Speciosa seed meal is in progress. [15]. a The optical rotation measurements were carried out based on their corresponding O-acetylated derivatives [11].…”