Synthetic, crystallographic, computational, and biological studies of 1,4-difluorobenzo[c]phenanthrene and its metabolites

1,4-Difluorobenzo[c]phenanthrene (1,4-DFBcPh) and its putative metabolites, the dihydrodiol and diol epoxides, have been synthesized and structurally characterized, and the extent of DNA binding by the metabolites has been assessed. 1,4-DFBcPh and 1,4-difluoro-10-methoxybenzo[c]phenanthrene were prepared by photochemical cyclization of appropriate naphthylphenylethylenes. The dihydrodiol was synthesized from 1,4-difluoro-10-methoxybenzo[c]phenanthrene, and the diol epoxides were diastereoselectively synthesized from the dihydrodiol. Interesting differences were noted in 1H NMR spectra of the series 1 (syn) diol epoxides of benzo[c]phenanthrene (BcPh) and 1,4-DFBcPh; the BcPh diol epoxide displays a quasi-diequatorial orientation of the hydroxyl groups, but in the 1,4-DFBcPh case these are diaxially disposed. This difference probably stems from the presence of the fjord-region fluorine atom in 1,4-DFBcPh. A through-space, fjord-region H-F coupling has also been observed for 1,4-DFBcPh and its derivatives. Comparative X-ray crystallographic analyses of BcPh and 1,4-DFBcPh and their dihydrodiols show that introduction of fluorine increases the molecular distortion by about 6-7 degrees . As a guide to estimating the molecular distortion and its effects, and for comparison with the X-ray structures in known cases, optimized structures of BcPh, 1,4-DFBcPh, and 1,4-DMBcPh (the dimethyl analogue) as well as their dihydrodiols and diol epoxides were computed. Relative aromaticities of these compounds were assessed by nucleus-independent chemical shift calculations, and 13C NMR chemical shifts were computed by gauge-inducing atomic orbital calculations. 1,4-DFBcPh and its dihydrodiol were subjected to metabolism, and the amount of DNA binding in human breast cancer MCF-7 cells was assessed. The extent of DNA binding was then compared with that for BcPh and its dihydrodiol and the potent carcinogen benzo[a]pyrene. The 1,4-DFBcPh series 2 (anti) diol epoxide-derived DNA adducts were also compared with those arising from intracellular oxidation of the dihydrodiol with subsequent DNA binding. These experiments showed that increased molecular distortion decreased metabolic activation to the terminal metabolites but that diol epoxide metabolites that are formed are the DNA-damaging species.     

Convenient syntheses of dibenzo[c,p]chrysene and its possible proximate and ultimate carcinogens: in vitro metabolism and DNA adduction studies

Dibenzo[c,p]chrysene (DB[c,p]C) is the only hexacyclic polycyclic aromatic hydrocarbon having two fjord regions, both in different chemical environments. Its environmental presence and relative tumorigenic potency are not known due to the lack of synthetic standards. We report here the synthesis of dibenzo[c,p]chrysene (1), its proximate carcinogens, i.e., trans-1,2-dihydroxy-1,2-dihydro-DB[c,p]C (2) and trans-11,12-dihydroxy-11,12-dihydro-DB[c,p]C (3), and possible ultimate carcinogens, i.e., anti-trans-1,2-dihydroxy-3,4-epoxy-1,2,3,4-tetrahydro-DB[c,p]C (4) and anti-trans-11,12-dihydroxy-13,14-epoxy-11,12,13,14-tetrahydro-DB[c,p]C (5). The syntheses of 1 and the appropriately methoxy-substituted DB[c,p]C (12 and 27), key intermediates for the synthesis of its proximate and ultimate metabolites, were tried first using a Suzuki cross-coupling reaction. However, the cyclization of olefins (10 and 11) gave poor yields of the desired products. An alternate method was thus developed employing a photochemical approach. The in vitro metabolism of DB[c,p]C was established with the S9 fraction of liver homogenate from phenobarbital/beta-naphthoflavone-induced Sprague-Dawley rats. The major dihydrodiol formed was identified as the fjord region 11,12-dihydroxy-11,12-dihydro-DB[c,p]C, while the major and minor phenols were identified as 11-hydroxy-DB[c,p]C and 12-hydroxy-DB[c,p]C, respectively. Further, the DNA adduction studies with the calf thymus DNA led to a mixture of dA and dG adducts for both fjord region diol epoxides (4 and 5). Interestingly, the dA to dG ratio for 1,2-dihydroxy-3,4-epoxide was much higher (3.2) compared to that of 11,12-dihydroxy-13,14-epoxide (0.5).     

Tetrahydroepoxides and diol epoxides of benz[c]acridine

The chemical synthesis and NMR characterization of the benzo ring tetrahydro- and diol epoxides of the carcinogen benz[c]acridine are described.     

Synthesis of benzo[c]phenanthrene dihydrodiols

Unlike most other alternant polycyclic aromatic hydrocarbons which are carcinogenic, benzo[c]phenanthrene has a “fjord region” instead of a “bay region”. For this reason, we have synthesized the three metabolically possible trans 1,2-, 3,4-, and 5,6-dihydrodiols to test them for carcinogenic activity.     

Palladium-catalyzed synthesis of nucleoside adducts from bay- and fjord-region diol epoxides

Palladium-catalyzed C-N bond formation has been utilized to synthesize covalent 2'-deoxyadenosine (dA) and 2'-deoxyguanosine (dG) adducts of benzo[a]pyrene (BaP) series 1 (syn) and benzo[c]phenanthrene (BcPh) series 2 (anti) diol epoxides. For this, (+/-)-10 alpha-amino-7 beta,8 alpha,9 beta-trisbenzoyloxy-7,8,9,10-tetrahydro BaP and (+/-)-1 beta-amino-2 alpha,3 alpha,4 beta-trisbenzoyloxy-1,2,3,4-tetrahydro BcPh were coupled with 6-halo-9-[3,5-bis-O-(tert-butyldimethylsilyl)-beta-D-erythro-pentofuranosyl]purine and O6-benzyl-3',5'-bis-O-(tert-butyldimethylsilyl)-2-bromo-2'-deoxyinosine, using a (+/-)-BINAP-Pd complex and Cs2CO3. For the synthesis of the dA adducts, both the 6-chloro- as well as the 6-bromopurine nucleoside derivatives were analyzed for the C-N coupling reaction with the hydrocarbon amino tribenzoates. With the BaP amino tribenzoate, the 6-chloronucleoside provided satisfactory results, whereas the 6-bromo analogue proved to be superior with the BcPh amino tribenzoate. Overall, lower yields of the dA adducts were obtained with the more hindered fjord-region BcPh amino tribenzoate as compared to the bay-region BaP amino tribenzoate. In contrast to reactions leading to the dA adducts, the C-N reactions of both BaP and BcPh amino tribenzoates with the 2-bromo-2'-deoxyinosine derivative proceeded in comparable yields. This seems to indicate that such Pd-catalyzed adduct forming reactions at the C-6 position may be influenced by steric constraints of the amine component, whereas those at the C-2 position are less sensitive. Diastereomeric adduct pairs were separated and characterized by spectral methods and by comparisons to adducts produced by direct displacement reactions as well as those formed from DNA alkylation by diol epoxides.     

Benzo[b] thiophene derivatives XVII. Electrophilic substitution of 4-hydroxybenzo[b] thiophene derivatives

A variety of eleclrophilic substitution reactions have been carried out on 4-methoxybenzo[b]-thiophene (IIIa) and 4-benzoyloxybenzo[b ] thiophene (IVa). Substitution occurs in the 7-position of IIIa and, with the exception of bromination, in the 7-position of IVa. Bromination of IVa occurs in the 3-position. Bromination of 4-hydroxybenzo[b] thiophene (IIa) occurs in the 5-position. The nmr spectra of eleven disubstituted benzo[b] thiophenes have been tabulated.     

A Synthesis of Two Novel Benzo[f]ninhydrin Analogs: 6-Methoxybenzo[f]ninhydrin and Thieno[f]ninhydrin

Improved methodology for the synthesis of benzo[f]ninhydrin (1) is described. The generality of this approach is illustrated with the synthesis of two novel analogs, 6-methoxybenzo[f]ninhydrin (3) and thieno[f]ninhydrin (4).     

Synthesis of 1,2-Epoxy-1,2,3,4-Tetrahydrobenzo[g]chrysene: The First Synthesis of a FJORD-Region Tetrahydroepoxide

This study describes the first synthesis of a fjord-region tetrahydroepoxide (11), derived from the carcinogenic hydrocarbon benzo[g]chrysene. This compound is a more potent DNA alkylating agent than the corresponding 3,4-diol 1,2-epoxide.     

Arene imine derivatives of chrysene and of benzo[g]chrysene: 1a,11c-dihydrochryseno[5,6-b]azirine and 1a,13c-dihydrobenzo[11,12]chryseno[5,6-b]azirine

The syntheses of the K-iraines (which are also benzo-bay-region derivatives) of chrysene ( 1 ) and benzo[g]-chrysene ( 2 ) are described. The preparation of 1a,11c-dihydrochryseno[5,6-b]azirine ( 5 ) was accomplished by treatment of 1a,11c-dihydrochryseno[5,6-b]oxirene ( 4 ) with sodium azide, and the mixture of trans-azido-alcohols 6 and 7 , so formed, was either cyclized with triethyl phosphite, or converted into E-6-azido-5-chloro-5,6-dihydrochrysene ( 8 ) followed by lithium aluminium hydride reduction. The synthesis of 1a,13c-dihydrobenzo-[11,12]chryseno[5,6-b]azirine ( 12 ) included the transformation of the corresponding oxide 11 into a mixture of E-9-azido-9,10-dihydrobenzo[g]chrysen-10-ol ( 13 ) and E-10-azido-9,10-dihydrobenzo[g]chrysen-9-ol ( 14 ), and reaction with tri-n-butylphosphine to give a mixture of Staudinger adducts 15 and 16 that underwent thermal decomposition into 12 upon heating in boiling dichloromethane.     

Benzo[b]thiophene derivatives I. 6-methoxybenzo[b]thiophene analogs of plant growth regulators

The acid catalyzed ring closure of an appropriately substituted phenyl ketoester sulfide served as the initial reaction in the synthesis of several 3,4- and 3,6-disubstituted benzo[b]thiophenes. One of these compounds, 4-methoxybenzo[b]thienyl-3-acetic acid, showed marked plant growth enhancement.     

Gas chromatographic-mass spectrometric analysis of diols and tetrols from reactions of polycyclic aromatic hydrocarbon epoxides with hemoglobin

We have evaluated both electron ionization (EI) and negative-ion chemical ionization (NICI) methods for the analysis of trimethylsilyl derivatives of a series of polycyclic aromatic hydrocarbon (PAH) alcohols including styrene diol, benzo[e]pyrene diol and tetrols, cyclopenta[c,d]pyrene diols, benzo[a]pyrene-4,5-diols, chrysene tetrols, benz[a]anthracene tetrols I and II, and syn- and anti-benzo[a]pyrene tetrols. NICI is the more sensitive method for all compounds except styrene diol. Detection limits are compound-dependent and range from 1 fmol for cyclopenta[c,d]pyrene diol to 1 pmol for benzo[e]pyrene diol. The EI detection limit for styrene diol is 60 fmol. PAH alcohols related to the compounds listed above were observed following hydrolysis of hemoglobin which had been reacted with PAH epoxides in vitro. Benzo[a]pyrene tetrols and a chrysene tetrol were observed following hydrolysis of hemoglobin isolated from human smokers' blood. Hydrolysis of styrene oxide treated hemoglobin in 18O-labeled water revealed at least two mechanisms of ester hydrolysis, including the BAL 1 pathway.     

Theoretical study of aza-polycyclic aromatic hydrocarbons (aza-PAHs), modelling carbocations from oxidized metabolites and their covalent adducts with representative nucleophiles

Protonation of the epoxides, diol epoxides, and dihydrodiols of benzo[h]quinoline (BhQ), benzo[f]quinoline (BfQ), phenanthrene (Phe), benzo[c]phenanthridine (BcPhen), and chrysene (Chry) were studied by DFT at the B3LYP/6-31G* level, and selected cases were calculated with the 6-31+G* diffuse-function augmented basis set for comparison purposes. Bay-region carbocations were formed from O-protonated epoxides via a barrierless processes. Relative carbocation stabilities were determined in the gas phase and with water as solvent (PCM method). The presence of a heteroatom changes the regioselectivity of epoxide ring opening, in some cases favoring non-bay-region carbocations. The epoxide ring opening mode is also greatly influenced by N-protonation. The dications resulting from initial N-protonation followed by epoxide protonation were also studied by DFT. Charge delocalization modes in the resulting mono- and dications were derived by GIAO-NMR (based on Delta delta13C values) and via the NPA-derived changes in charges. Relative aromaticity in different rings in the arenium ions was gauged by NICS. In representative cases, the covalent adducts (syn and anti) formed by reaction of the benzylic carbocations derived from diol epoxides and dihydrodiols with methoxide and methanethiolate anions were studied. Relative energies (in the gas phase and with water as solvent) and geometries of the adducts formed by quenching of the carbocations derived from BhQ and Phe-epoxides with guanine via the exocyclic amino group and via the N-7 were also investigated computationally. Although aqueous phase calculations change the energy for the addition reactions because of greater stabilization of the reactants, relative reactivity trends remain the same. The data are discussed, taking into account the available experimental results concerning the biological activity of these compounds.     

Solvent-free synthesis of benzo[a]pyrene 7,8-diol 9,10-epoxide adducts at the N(2)-position of deoxyguanosine

[reaction: see text] The first solid-state (or solvent-free) synthesis of protected deoxyguanosine (dG) adducts of benzo[a]pyrene diol epoxides at room temperature is reported. Whereas dG adducts derived from cis- and trans-opening of (+/-)-7beta,8alpha-dihydroxy-9beta,10beta-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (DE-1 1) are formed as a 1:1 mixture, the direct opening of the diastereomeric (+/-)-7beta,8alpha-dihydroxy-9alpha,10alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (DE-2, 2) produced a 15:85 ratio favoring the trans-opened dG adduct 7.     

Synthesis of monofluorobenzo[c]phenanthrenes

Synthesis of 1-, 2-, 3- and 4-fluorobenzo[c]phenanthrenes by photocyclization of appropriate β-naphth-l-yl fluorostyrenes is described. An improved synthesis of 6-fluorobenzo[c]phenanthrene was developed. Partial photochemical debromination occured upon cyclization of 2-bromo-7-fluorobenzo[c]phenanthrene.     

Synthesis of Boronate‐Based Benzo[fg]tetracene and Benzo[hi]hexacene via Demethylative Direct Borylation

A demethylative direct borylation is reported, which was applied to the synthesis of benzo[fg]tetracenes containing boronate ester, amide, and thioester substructures. Depending on the heteroatom adjacent to boron, the molecules showed characteristic photophysical properties, molecular arrangements, and chemical stabilities. The key to the successful synthesis is the appropriate choice of the boron source and Brønsted base. The versatility of the direct borylation was demonstrated by the synthesis of a boronate‐based benzo[hi]hexacene.     

New synthetic approaches to polycyclic aromatic hydrocarbons and their carcinogenic oxidized metabolites: derivatives of benzo[s]picene, benzo[rst]pentaphene, and dibenzo[b,def]chrysene

A new synthetic approach to polycyclic aromatic compounds is described that entails in the key steps double Suzuki coupling of PAH bisboronic acid derivatives with o-bromoaryl aldehydes to furnish aryl dialdehydes that are converted to larger polycyclic aromatic ring systems by either (a) conversion to diolefins by Wittig reaction followed by photocyclization or (b) reductive cyclization with triflic acid and 1,3-propanediol. This synthetic method provides convenient access to as many as three different polycyclic aromatic ring systems from a single Suzuki coupled intermediate. It was utilized to synthesize substituted derivatives of benzo[s]picene, benzo[rst]pentaphene, dibenzo[b,def]chrysene, and 13,14-dihydro-benz[g]indeno[2,1-a]fluorene, as well as the putative carcinogenic bisdihydrodiol metabolites of benzo[s]picene, benzo[rst]pentaphene, and dibenzo[b,def]chrysene.     

Benzo[g]isoquinolinium benzoylmethylids

Stable benzo[g]isoquinolinium methylids were obtained from N-phenacylbenzo[g]isoquinolinium bromides and two of its benzene ring-substituted analogs. The first of these quaternary salts was converted to benzo[g]isoquinolinium dibenzoylmethylid. 3-Benzoyl-l,2-dicarbomethoxynaphth[2,3-g]indolizine was obtained from the same salt with dimethyl acetylenedicarboxylate (via a 1,3-dipolar cycloaddition reaction). Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 806–807, June, 1980     

Synthesis, properties, and oxidizing ability of 9,11-dimethylbenzocyclohepta[6,7-b]pyrimido[5,4-d]furan- 10(9H),12(11H)-dionylium tetrafluoroborate

Convenient preparation of novel 9,11-dimethylbenzocyclohepta[6,7-b]pyrimido[5,4-d]furan-10(9H),12(11H)-dionylium tetrafluoroborate 11*BF4- consisted of a condensation reaction of benzo[d]tropone with dimethylbarbituric acid and following oxidative cyclization reaction by using DDQ-Sc(OTf)3 or photoirradiation under aerobic conditions. Alternative synthesis of 11*BF4- was also accomplished by a condensation reaction of 2-methoxybenzo[d]tropone with dimethylbarbituric acid and a subsequent cyclization reaction by using 42% aq HBF4. The X-ray crystal analysis and MO calculation were carried out to clarify the structural characteristics. Properties of the cation 11 were studied by the pKR+ value (4.7) and reduction potentials (-0.46 and -1.07 V vs Ag/AgNO3) as well as the reaction with some nucleophiles. The oxidizing ability of 11*BF4- toward alcohols in the autorecycling process was demonstrated as well.     

Synthesis of 4,5-Disubstituted Benzo[c][2,7]naphthyridines by Combined Metalation-Palladium-Catalysed Cross-Coupling Strategies. Preparation of 8h-Pyrido[4,3,2-mn]acridone as a Model of Cystodytin Alkaloids

A short and efficient synthesis of 8H-pyrido[4,3,2-mn]acridone is described. The strategy involves the preparation of 4-chloro-5-methylbenzo[c][2,7]naphtyridine, as key intermediate, by metalation and Palladium catalyzed cross-coupling reaction. A second cross-coupling reaction and subsequent oxydation by SeO₂ led to the title compound.     

Chirality and conformational changes in 4-phenylphenanthrenes and 1-phenylbenzo[c]phenanthrene derivatives

NMR data of several 4-phenylphenanthrenes (15, 16) have revealed that the crowding in these compounds does not lead to chirality at temperatures as low as ?90°. The easy rotation of the phenyl substituent observed by NMR implies that notwithstanding the phenanthrene moiety in average behaves as a planar part the phenyl group does not experience steric hindrance.The analysis of temperature-dependent NMR spectra of several derivatives of 1-phenylbenzo[c]phenanthrenes (17-20) indicated that in these compounds exchange processes do occur. By calculations of the free energies of activation from the NMR data two processes could be distinguished: rotation of the phenyl substituent at one side of the helical benzo[c]phenanthrene moiety, for which ΔG^XXX_rot , is ca. 13.0$\text{kcal}\text{mol}$ or slightly larger when bulky substituents are present at C₂, and racemisation by a rotation of the phenyl group around the opposite end of the benzo[c]phenanthrene skeleton with simultaneous inversion of the helical conformation. For this process ΔG^XXX_rac is ca. 16$\text{kcal}\text{mol}$. The results have been compared with comparable data of related compounds like 1.8-diphenylnaphthalene, hexahelicene, and 4-methylbenzo[c] phenanthrenes, and gave evidence for the remarkably small, space-demanding properties of the phenyl substituent in these compounds.