Benzylic Adducts Research Articles

Photochemical Synthesis of Benzylisoquinoline Alkaloids Using Tetra-coordinate Benzylboron Reagents: Application to Berberine Type Alkaloids

Abstract Photochemical and selective synthesis of 1-benzyl-1,2-dihydroisoquinolines was achieved from isoquinolines, methyl chloroformate and electron-rich benzyltrifluoro-borates in the presence of pyridine that inhibited subsequent formation of possible cyclized pavine type products. The benzyl adducts were successfully transformed into berberine type skeletons by the cyclization at the carbamate moiety.

O4 -Alkylated-2-Deoxyuridine Repair by O6 -Alkylguanine DNA Alkyltransferase is Augmented by a C5-Fluorine Modification.

Oligonucleotides containing various adducts, including ethyl, benzyl, 4-hydroxybutyl and 7-hydroxyheptyl groups, at the O4 atom of 5-fluoro-O4 -alkyl-2'-deoxyuridine were prepared by solid-phase synthesis. UV thermal denaturation studies demonstrated that these modifications destabilised the duplex by approximately 10 °C, relative to the control containing 5-fluoro-2'-deoxyuridine. Circular dichroism spectroscopy revealed that these modified duplexes all adopted a B-form DNA structure. O6 -Alkylguanine DNA alkyltransferase (AGT) from humans (hAGT) was most efficient at repair of the 5-fluoro-O4 -benzyl-2'-deoxyuridine adduct, whereas the thymidine analogue was refractory to repair. The Escherichia coli AGT variant (OGT) was also efficient at removing O4 -ethyl and benzyl adducts of 5-fluoro-2-deoxyuridine. Computational assessment of N1-methyl analogues of the O4 -alkylated nucleobases revealed that the C5-fluorine modification had an influence on reducing the electron density of the O4 -Cα bond, relative to thymine (C5-methyl) and uracil (C5-hydrogen). These results reveal the positive influence of the C5-fluorine atom on the repair of larger O4 -alkyl adducts to expand knowledge of the range of substrates able to be repaired by AGT.

NMR spectroscopic study of the adduct formation and reactivity of homoleptic rare earth amides with alkali metal benzyl compounds, and the crystal structures of [Li(TMEDA)2][Nd{N(SiMe3)2}3(CH2Ph)] and [{Li(TMP)}2{Li(Ph)}

An NMR spectroscopic study has been conducted into the reactivity of alkali metal benzyls [M(CH2Ph)], (M = Li, Na, K) with lanthanide tris(amide) complexes [Ln(N″)3] (Ln = Y, Ce, Nd; N″ = N(SiMe3)2) and [Ce(TMP)3] (TMP = 2,2,6,6-tetramethylpiperidide). It was found that for [Ln(N″)3], benzyl adducts [M][Ln(N″)3(CH2Ph)] were initially formed, and the molecular structure for M = Li(TMEDA)2 and Ln = Nd was determined revealing a distorted tetrahedral [Nd(N″)3(CH2Ph)] anion. In all cases, these adduct complexes were unstable, intramolecularly deprotonating a methyl arm of a N″ ligand via benzyl basicity and eliminating toluene to prepare cyclometallated complexes of the form [M][Ln(N″)2{κ2-CH2Si(Me)2N(SiMe3)}]. In parallel studies, reactions of [Li(Ph)] with [Ln(N″)3] (Ln = Ce, Nd) afforded [Li(N″)], whilst for (Ln = Y) adduct formation was observed. [Ce(TMP)3] did not generate any characterisable bimetallic adducts. The reaction of [Li(Ph)] with [Li(TMP)] afforded the hexanuclear [{Li(TMP)}2{Li(μ-Ph)}]2, which features lithium in three different coordination environments.

Formation of Benzylic−DNA Adducts Resulting from 7,12-Dimethylbenz[a]anthracene in Vivo

Studies were undertaken to determine the formation of benzylic-DNA adducts in rats administered 7,12-dimethylbenz[a]anthracene (DMBA) and its meso-region metabolites by subcutaneous injection. Here, we show that 7-hydroxymethyl-12-methylbenz[a]anthracene (7-HMBA) and 7-sulfoxymethyl-12-methylbenz[a]anthracene (7-SMBA) gave rise to some benzylic-DNA adducts indistinguishable from adducts formed from DMBA. Adducts were analyzed by butanol enrichment-mediated 32P-postlabeling assay. Female Sprague-Dawley rats given a combined dose of 420 micromol DMBA/kg b. wt resulted in two major and up to nine minor adducts in the subcutaneous tissue, with chromatographic resemblance to benzylic-DNA adducts prepared in vitro. Subcutaneous administration of 7-HMBA, 7-SMBA, and 7-methyl-12-hydroxymethylbenz[a]anthracene (12-HMBA) (210, 42, and 210 micromol/kg b. wt, respectively) each resulted in one major and several minor benzylic-DNA adducts. From cochromatography with reference adducts, it was concluded that the benzylic DNA adduct 4, derived from the parent compound, comigrates with the major adduct from 7-HMBA and 7-SMBA, whereas adducts 2 and 3 comigrate with adducts resulting from 12-HMBA and 7-methyl-12-sulfooxymethylbenz[a]anthracene, respectively. These data suggest that 7-sulfooxymethyl- and 12-sulfooxymethy derivatives produce distinct adducts. Several major and minor diol epoxide-related DNA adducts were also detected. The diol epoxide- and benzylic-DNA adducts were found in a 2:1 ratio. The oral, intraperitoneal, and intramammiliary treatments with DMBA showed no detectable benzylic adducts in the liver and mammary glands 24 h after the last treatment, although the adduct formation was clearly evident with SMBA and/or HMBA treatments, suggesting that hydroxylation of DMBA to form HMBA may be the rate-limiting step for the meso-methyl substitution pathway. The present study clearly demonstrates the in vivo formation of benzylic-DNA adducts from DMBA. The data also reveal the involvement of the 12-methyl group of DMBA in adduct formation.

Detection of benzylic adducts in DNA and nucleotides from 7-sulfooxymethyl-12-methylbenz[ a]anthracene and related compounds by 32P-postlabeling using new TLC systems

7,12-Dimethylbenz[ a]anthracene (DMBA) is a highly potent experimental carcinogen, that must be transformed to its ultimate carcinogenic form in vivo. The meso-region theory of aromatic hydrocarbon carcinogenesis predicts that 7-hydroxymethyl sulfate (7-HMBA) ester plays a major role in the metabolic activation, benzylic DNA adduct formation and complete carcinogenicity of HMBA and DMBA. This study was undertaken to detect highly lipophilic benzylic DNA adducts resulting from the reaction between 7-hydroxymethy sulfate ester of HMBA (7-SMBA) and DNA as well as determine their DNA base selectivity. Synthetic 7-SMBA was incubated with DNA (800 μg/ml) and individual deoxynucleoside 3′-monophosphates (600 μg/ml) and benzylic adducts were analyzed by 32P-postlabeling/TLC following their enrichment with butanol extraction. Dilute ammonium hydroxide-based solvents were developed to detect the highly lipophilic aralkyl adducts. The reaction with DNA, dGp and dAp gave rise to multiple adducts; dCp and dTp showed no significant adducts. Chromatographic comparison revealed that the major DNA adduct was derived from dG. The methodology developed was also found applicable for highly lipophilic adducts resulting from sulfate esters of structurally-related metabolites of DMBA.

N-Nitrosobenzylmethylamine is activated to a DNA benzylating agent in rats.

The ability of rat tissues to activate the esophageal carcinogen, N-nitrosobenzylmethylamine (NBzMA), to a DNA benzylating intermediate was investigated. [3-3H]NBzMA was prepared and given to male F344 rats. Tissues were harvested 4 h after treatment, and DNA was isolated. HPLC analysis with radiochemical detection of chemical and enzymatic hydrolysates of DNA from liver and lung revealed the formation of benzyl adducts. Benzyl alcohol, N2-benzylguanine, 3-benzyladenine, N6-benzyladenine, and 7-benzylguanine were the major radioactive components in the hydrolysates. An unknown adduct was also observed. The adduct distribution was similar to that observed in [3-3H]benzylnitrosourea ([3-3H]BzNU)-treated calf thymus DNA. However, enzymatic hydrolysates of [3-3H]BzNU-treated DNA also contained significant levels of O6-benzyl-2'-deoxyguanosine (O6-BzdG). This radioactive adduct disappeared upon incubation of the DNA with a crude preparation of the repair protein, O6-alkylguanine-DNA alkyltransferase isolated from rat liver. These data provide evidence that O6-BzdG is probably rapidly repaired in vivo. No benzylation of esophageal mucosal DNA was detected. The level of DNA benzylation observed in tissues from [3-3H]NBzMA-treated rats was several orders of magnitude lower than the level of DNA methylation in these same tissues. Therefore, these data indicate that DNA benzylation plays a minor role, if any, in the carcinogenic activity of NBzMA.

Unequivocal synthesis of meso-tetraphenyltetrabenzoporphine

The reaction of 3-benzylidenephthalimidine (3-BPI) with zinc benzoate as a chelating agent has led to the only tetramerization of 3-BPI to yield meso-tetraphenyltetrabenzoporphinato zinc (ZnTPTBP), while the use of zinc acetate has provided a complicated mixture of ZnTBPs with meso-phenyl substituent(s), the number of which is from one to four. From the FD-MS data and 3D(dimensional)-HPLC analysis, it is shown that this reaction product is contaminated with the benzyl adducts of ZnTPBP. This benzyl fragmentation probably occurs by the high temperature pyrolysis of 3-BPI.

Metabolic activation of the carcinogen 6-hydroxymethylbenzo[a]pyrene: formation of an electrophilic sulfuric acid ester and benzylic DNA adducts in rat liver in vivo and in reactions in vitro.

Hydroxylation of meso-methyl groups with subsequent formation of reactive electrophilic esters has been proposed as a possible activation pathway in the metabolism, DNA binding and carcinogenicity of some methyl-substituted polycyclic aromatic hydrocarbons. Some data in vitro have been reported in support of this concept. In this study, sulfotransferase activity for 6-hydroxymethylbenzo[a]pyrene (HMBP) in rat and mouse liver cytosols was demonstrated to mediate formation of benzylic adducts from this hydrocarbon with guanosine and with deoxyguanosine and deoxyadenosine in DNA. These benzylic adducts were also obtained from reactions of synthetic 6-sulfooxymethylbenzo[a]pyrene (SMBP) with individual (deoxy)ribonucleosides or DNA. The structure of the major DNA adduct formed from HMBP and SMBP was determined from NMR spectroscopy to be N2-(benzo[a]pyrene-6-methylenyl)-deoxyguanosine. Low levels of a deoxycytidine adduct were also obtained from DNA reacted with SMBP. Covalent modification of DNA by acetyl-CoA- and ATP-dependent activation of HMBP also produced the identical benzylic adducts, but the amounts were smaller than those obtained in the sulfotransferase-mediated reaction. The i.p. administration of HMBP to rats resulted in the formation of a hepatic DNA adduct. After enzymatic hydrolysis to the nucleoside level, this DNA adduct was chromatographically identical with the deoxyguanosine adduct formed in the above in vitro reactions. This adduct accounted for approximately 20-30% of total HMBP residues bound to hepatic DNA and its formation was significantly inhibited by pretreatment of rats with dehydroepiandrosterone, an inhibitor of the sulfotransferase activity for HMBP. The i.p. administration of comparable doses of SMBP to rats led to the formation of much larger amounts of the adducts with the guanine, adenine, and cytosine bases in the liver DNA. The data indicate that the sulfotransferase activity in the rat liver for HMBP plays a major role in the benzylic DNA adduct formation from this hydrocarbon in rat liver in vivo.