The change in DNA conformation produced by the attachment of a reactive substance is likely to be a vital factor in determining the biological consequences of the reaction. We have prepared a deoxydinucleoside monophosphate containing the major adduct derived from the carcinogenic amine 4-aminobiphenyl and analyzed its conformation by theoretical and experimental methods. Reaction of d(CpG) with N-acetoxy-N-(trifluoroacetyl)-4-aminobiphenyl afforded the product modified at C-8 of guanine with 4-aminobiphenyl. After purification by reverse-phase high-performance liquid chromatography, milligram amounts of product were obtained. It was analyzed by circular dichroism, proton magnetic resonance, and minimized potential-energy calculations. A flexible molecule with a mixture of conformers is indicated. Both carcinogen-base-stacked states and base-base-stacked states, with guanine both syn anti, contribute to the population mixture on the dimer level. The global minimum-energy conformation has syn-guanine and carcinogen-base stacking. Forms of this type are calculated to represent roughly 58% of the conformer population. Because of the twisted nature of the biphenyl moiety, carcinogen-base stacking inherently involves less overlap than that in the planar and rigid three-ringed aminofluorene analogue. This difference might relate to the diminished effectiveness of the aminobiphenyl vs. the aminofluorene adduct as a frameshift mutagen in Salmonella typhimurium 1538.

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The effect of temperature on the esr spectra of a number of medium-sized cycloalkanesemidiones has been investigated. The effect of temperature on the population of the equatorial (more stable) and axial conformations of the methylcyclohexanesemidiones yields enthalpy differences of 0.7 and 1.4 kcal/mole (AS s 0) for the 3-and 4-methyl substituents. The treatment is extended to di-and trialkylated cyclohexanesemidiones. Cyclohexanesemidione and several symmetrically substituted derivatives yielded coalescence temperatures and demonstrated line-broadening effects above and below the coalescence temperature. Coalescence temperatures occur at conformational lifetimes of -lo-' sec. Cyclohexanesemidione undergoes the interconversion of halfchair conformations with an enthalpy of activation of 4.0 kcal/mole, entropy of activation fl eu. 3,3-Dimethyl-or 4,4-dimethylcyclohexanesemidiones have similar enthalpies of activation (3.9, 3.2 kcal/mole) but less favorable entropies of activation (-6, -8 eu). 3,3,5,5-Tetramethylcyclohexanesemidione has an enthalpy of activation of only 2.6 kcal/mole but the entropy of activation for ring inversion is -8 eu. The treatment has been extended to N-methylpiperidine-3,4-semidione which is much more conformationally stable than cyclohexanesemidione (coalescence temperature -+60 and -85 O, respectively) and to cycloheptanesemidione for which a coalescence temperature could not be observed because of conformational stability.he oxidation of a variety of ketones in basic solu-

The modified dinucleoside monophosphate, N-[deoxycytidylyl-(3'-5')-guanosin-8-yl]aniline (dCprG-An) has been prepared by the phosphotriester synthesis approach, using suitably blocked derivatives of dCp and N-guanosin-8-ylaniline (rG-An). The latter compound was synthesized by a route that featured nucleophilic displacement by antiline upon an 8-bromoguanosine derivative. A number of attempts to prepare N-(deoxyguanosin-8-yl)aniline (dG-An) by electrophilic substitution, using activated aniline derivatives, failed. Nucleophilic substitution reactions of aniline with 8-bromodeoxyguanosine derivatives afforded only the base, N-guanin-8-ylaniline. The conformation of dCprG-An has been studied by CD, proton magnetic resonance, and minimized potential energy calculations. A flexible molecule with a mixture of conformers is indicated. Base-base stacked states predominate, in contrast to the case of a dimer containing 4-aminobiphenyl bound to the 8-position of guanine, where carcinogen-base stacked states are dominant. The mutagenic and carcinogenic activities of aniline are much less than those of many polycyclic aromatic amines. The diminished stacking ability of the aniline ring, as well as the weak electrophilic reactivity of activated aniline derivatives, may be a cause of this weak biological activity.

The carcinogen N-acetoxy-N-2-acetylaminofluorene reacts with dG and dG-containing nucleotides to give good yields of the C-8 adducts, but the analogous 4-aminobiphenyl derivative does not. Replacement of the N-acetoxy group by 2,6-dichlorobenzoyloxy circumvents this difficulty. This reaction is shown to be generally applicable, and biphenylamido adducts with dG, d(CpG), d(GpC) and d(ApG) have been prepared. A new, useful deacetylation procedure employing the heterogeneous system sodium carbonate/methanol which leads to the corresponding biphenylamino derivative without appreciable imidazole ring opening is also reported.