Stable ion study of benzo[a]pyrene (BaP) derivatives: 7,8-dihydro-BaP, 9,10-dihydro-BaP and its 6-halo derivatives, 1- and 3-methoxy-9,10-dihydro-BaP-7(8H)-one,as well as the proximate carcinogen BaP 7,8-dihydrodiol and its dibenzoate,combined with a comparative DNA binding study of regioisomeric (1-, 4-, 2-) pyrenylcarbinols

A stable ion study of a series of BaP derivatives is reported. 7,8-Dihydro-BaP 1 gives a persistent bay-region benzyliclike carbocation which shows extensive charge delocalization into the pyrene moiety. In contrast, a "benzylic" carbocation can not be generated from 9,10-dihydro-BaP 2. Introduction of bulky substituents at peri C-6 of 9,10-dihydro-BaP (as in 4 and 5) prevents side reactions (dimerization) to the extent that the initially formed carbocation undergoes rearrangement to generate the corresponding bay-region "benzylic" carbocation as a persistent species. Introduction of methoxy substituents into the 1- or 3-positions of 9,10-dihydro-BaP-7(8H)-one (6,7) increases its electrophilic reactivity to the extent that stable carboxonium-arenium dications are produced in FSO3H-SO2ClF. A detailed NMR study (at 500 MHz) of the resulting mono- and dications is reported, and charge delocalization mode (as well as conformational aspects) are addressed. Other oxidized derivatives of BaP such as the 7,8-dihydrodiol 9 and the 7,8-dihydrodibenzoate 8 are not suitable models for stable ion study because of competing O-protonation (and elimination). Energies for various possible arenium ions and regioisomeric "benzylic" cations were computed by the DFT method at the B3LYP/6-31G(d)//B3LYP/6-31G(d) level or by AM1 for comparison with the experimental results. These findings provide further evidence in support of the stability sequence: 1-pyrenyl > 4-pyrenyl > 2-pyrenyl in alpha-pyrene-substituted carbocations as models for the intermediates arising from BaP-epoxide ring opening. In an effort to provide a parallel, a series of alpha-pyrenylcarbinols were subjected to a DNA binding study using human MCF-7 cells. The results/trends are discussed and compared with the stable ion data.     

8-Hydroxyquinoline Based Multipodal Systems: Effect of Spatial Placement of 8-Hydroxyquinoline on Metal Ion Recognition

The complexation behaviors of tetrapod 1,2,4,5-tetrakis(8-hydroxyquinolinoxymethyl) benzene (1) and dipod 1,2-bis(8-hydroxyquinolinoxymethyl)benzene (2) have been determined by fluorescence spectroscopy in CH₃CN–H₂O (4:1) buffered at pH 6.9 [HEPES 10 mM] and by ¹H NMR in CD₃CN-CDCl₃ (1:1) mixture. Tetrapod 1 can recognize Ag⁺(10–40 μM) even in the presence of (500 μM) of alkali and alkaline earth metal ions. However, transition metal ions interfere in the estimation of Ag⁺. Dipod 2 shows poor selectivity towards Ag⁺. The ¹H NMR based titrations of podands 1 and 2 against AgNO₃ show characterstic changes in chemical shifts in quinoline, methylene and aromatic protons. The spectral fitting of fluorescence and ¹H NMR titration data has been used to evaluate the stoichiometries of complexes and their complexation constants.     

Dihydrodiols and diol epoxides of dibenzo[a,i]-and [a,h]pyrene

Syntheses of dihydrodiols and highly mutagenic diol epoxides of the carcinogenic polycyclic aromatic hydrocarbons dibenzo[a,i]-and [a,h]pyrene are described.     

Adventures in Tin(II) phosphinidene chemistry; insights into the mechanism of P-P and Sn-Sn bond formation

The reactions of the Sn(II) dimethylamido reagent Sn(NMe₂)₂ with alkali metal primary phosphides [RPHM] give a range of heterometallic Sn(II) phosphinidene compounds, depending on the organic substituents (R) and the alkali metal (M). For less sterically demanding substituents and/or for the heavier alkali metals, the formation of P-P and Sn-Sn bonded complexes occurs. Structural studies of the reaction products with a range of R-groups and alkali metals cast light on the mechanisms involved in this new type of reaction.     

Reactivity of ionic liquids

Ionic liquids are becoming widely used in synthetic organic chemistry and yet relatively little attention has been paid to the intrinsic reactivity of these low temperature molten salts. Clues to the non-innocent nature of many ionic liquids are contained in the reports of altered reactivity of dissolved substrates, unexpected catalytic activity and unforeseen by-product formation. In this review, we focus on the reactivity of ionic liquids, as opposed to reactivity in ionic liquids (although discussion of the latter is often included where it aids understanding of the former).     

Synthetic Ionophores. 13. Pyridine-Diamide-Diester Receptors: Remarkable Effect of Amide Substituents on Molecular Organization and Ag(+) Selectivity

The N(Py).HN(amide) hydrogen bonding within the macrocyclic cavities in 9, 10, and 13 invokes their symmetrical electron-deficient structures ((1)H NMR) and consequently bind with water. This results in their poor ionophore characters. The steric requirement of methyl/benzyl substituents on amide N in 11 and 12 takes the substituents out of the cavity and thus positions the amide O toward the cavity ((1)H, (13)C NMR and X-ray analysis). This arrangement of two pyridine N and two amide O ((13)C NMR, IR) binding sites provides an appropriate environment for selective binding toward Ag(+) over Pb(2+), Tl(+), alkali, and alkaline earth cations. The increased spacer length in 14 leads to a lop-sided twist of pyridine rings (X-ray) and disturbs the above arrangement and leads to its poor binding character.     

A New and Concise Synthesis of 3-Hydroxybenzo[c]phenanthrene and 12-Hydroxybenzo[g]chrysene, Useful Intermediates for the Synthesis of Fjord-Region Diol Epoxides of Benzo[c]phenanthrene and Benzo[g]chrysene

A new strategy which involves a palladium-catalyzed cross-coupling reaction has been developed for the rapid synthesis of 3-hydroxybenzo[c]phenanthrene (5) and 12-hydroxybenzo[g]chrysene (6). These phenolic compounds are the key intermediates for the synthesis of highly carcinogenic fjord-region diol epoxide metabolites 3 and 4 of benzo[c]phenanthrene (1) and benzo[g]chrysene (2). The cross-coupling reaction of 2-bromo-5-methoxybenzaldehyde (9) with naphthalene-1-boronic acid (7) and phenanthrene-9-boronic acid (8) produced 2-(1-naphthyl)-5-methoxybenzaldehyde (10) and 2-(9-phenanthryl)-5-methoxybenzaldehyde (11), respectively, in quantitative yields. After reaction of these aldehydes with trimethylsulfonium iodide under phase-transfer conditions or with the Wittig reagent obtained from (methoxymethyl)triphenylphosphonium bromide and phenyllithium to generate an oxiranyl or methoxyethene side chain, the acid-catalyzed cyclization with methanesulfonic acid (or boron trifluoride) produced 3-methoxybenzo[c]phenanthrene (16) and 12-methoxybenzo[g]chrysene (17) in 61-64% yields. Finally, demethylation of these methoxy derivatives 16 and 17 with boron tribromide resulted in the formation of the hydroxy analogues 5 and 6, respectively. The availability of this short and high-yielding regiospecific method for the synthesis of phenols 5 and 6 should allow the preparative-scale synthesis of the fjord-region diol epoxides 3 and 4. These diol epoxides are required as starting compounds for the synthesis of site-specifically modified oligonucleotides which are critically needed to elucidate the mechanism of carcinogenesis at the molecular level.     

Chemical and biotechnological developments in organotin cancer chemotherapy

This review provides a substantial knowledge on the action mode of organotins in cancer chemotherapy. The coordinating ability of organotin compounds towards DNA and cancer cells is discussed. Most of the organotins tested are DNA-targeted and mitotic, the action mode occurring via a gene-mediated pathway. These potential anti-cancer drugs are actually being studied widely, and whilst they are efficacious and perhaps curative against a select number of neoplasias, suffer from a variety of deficiencies, notably severe systemic toxicity and a tendency to elicit drug resistance.     

Synthesis of trans‐dihydrodiol derivatives of phenanthro[3,4‐b]‐thiophene and phenanthro[4,3‐b]thiophene

The present study describes the synthesis of phenanthro[3,4‐b]thiophene (3) , phenanthro[4,3‐b]thiophene (4) and its potential dihydrodiol metabolites, trans‐6,7‐dihydroxy‐6,7‐dihydrophenanthro[3,4‐b]thiophene (5) and trans‐8,9‐dihydroxy‐8,9‐dihydrophenanthro[3,4‐b]thiophene (6) , trans–6,7‐dihydroxy‐6,7‐dihydro‐phenanthro[4,3‐b]thiophene (7) and trans‐8,9‐dihydroxy‐8,9‐dihydrophenanthro[4,3‐b]thiophene (8) from Suzuki coupled intermediates. The UV spectra of these dihydrodiols are presented. These spectra are useful tools for identifying these dihydrodiols among unknown metabolites of 1 and 2 produced in vitro or in vivo.