SYNTHESIS AND CHARACTERIZATION OF ADDUCTS DERIVED FROM THE SYN-DIASTEREOMER OF BENZO[A]PYRENE 7,8-DIHYDRODIOL 9,10-EPOXIDE AND THE 5'-D(CCTATAGATATCC) OLIGONUCLEOTIDE

5'-d(CCTATAGATATCC) was reacted with each syn-enantiomer of trans-7,8- dihydroxy 9,10-epoxy 7,8,9,10-tetrahydrobenzo[a]pyrene (syn-BPDE). The (-)-enantiomer yielded one dominating adduct, whereas the (+)-enantio mer resulted in two major adducts. As indicated by optical spectroscop ic methods, the major adduct derived from both (-)- and (+)-syn-BPDE i nvolves cis addition of the C-10 position of the diol epoxide to the e xocyclic amino group of deoxyguanosine [(-)-syn-BPDE(c)-N-2-dG and (+) -syn-BPDE(c)-N-2-dG, respectively], whereas the minor (+)-syn-BPDE add uct is identical to a trans adduct [(+)-syn-BPDE(t)-N-2-dG]. The cis a dducts as well as the (+)-syn-BPDE(t)-N-2-dG adduct are chemically sta ble for several weeks when stored at less than or equal to 4 degrees C in darkness. In duplexes composed of (-)-syn-BPDE,-N2-dG or (+)-synBP DE(c)-N-2-dG or (+)-syn-BPDE(c)-N-2-dG modified 5'-d(CCTATAGATATCC) an d the complement 5'-d(GGATATCTATAGG), the presence of an adduct, in pa rticular the latter, substantially decreased the T-m value relative to the corresponding unmodified duplex. Addition of 5'-d(GGATATCTATAGG) or strands in which dC was replaced with dT, dG, or dA to (-)-syn-BPDE (c)-N-2-dG modified 5'-d(CCTATAGATATCC) decreased the fluorescence int ensity in all cases (25-45%). In similar experiments with the (+)-syn- BPDE(c)-N-2-dG adduct, dC or dT opposite the adduct decreased the fluo rescence intensity, whereas dA and dG caused an increase. With the (+) -syn-BPDE(t)-N-2-dG adduct, duplex formation had no effect on the inte nsity with dC or dG opposite the adduct, while an increase could be no ted with dT or dA. Acrylamide had no significant effect on the fluores cence intensity of duplexes with cis adducts in contrast to the marked quenching of the fluorescence of (+)-syn-BPDE(t)-N-2-dG oligonucleoti de duplexes. In single stranded form, both the cis adducts exhibited a bsorption and fluorescence excitation maxima at 352-353 nm while the ( +)-syn-BPDE(t)-N-2-dG adduct was around 350-351 nm. Addition of the co mplement or the sequence in which dA replaced dC to the (+)-syn-BPDE(t )-N-2-dG adduct shifted the maxima to 347-349 nm, whereas addition of sequences containing dT or dG opposite the adduct affected the fluores cence maxima but had no effect on absorption maxima. Formation of dupl exes with the cis adducts had no or very little effect on the absorpti on and fluorescence maxima. In conclusion, the results of this study i mply an intercalative mode of interaction of the pyrenyl chromophores of the cis adducts and external localization of the (+)-syn-BPDE(t)-N- 2-dG adduct.