pH-Dependent conformational changes in bisporphyrincalix[4]arene

pH-Dependent conformational changes in bisporphyrincalixarene in which the calix[4]arene core fixes the tetrapyrrole chromophores in the cyclophane orientation relative to each other were studied by spectrophotometric titration and ¹H NMR spectroscopy. It was shown that the distance between the reaction centers of the porphyrin fragments of the macrocycle can be controlled by varying the solution acidity. The ranges of reagent concentrations where functionally significant reversible conformational changes of the dimeric porphyrin occur were determined.     

Chirality and conformational changes in 4,5-diaryltriphenylenes

Line-shape analysis of temperature dependent NMR spectra of several substituted 4,5-diphenyl-triphenylenes has been performed to determine the free energy of activation for rotation (ΔG_rot^*) of the phenyl groups. The rotational barrier (ΔG_rot^*) depends on the presence and position of substituents on the phenyl groups; it is the largest in compounds with ortho-substituents. The independent determined free energy of activation of racemization (ΔG_rac^*) is about equal to ΔG_rot^* in 4-phenyl-5-(3,5-dimethylphenyl)triphenylene, but in 4,5-bis-(3,5- dimethylphenyl) triphenylene ΔG_rac^* is much larger than ΔG_rot^*. It is concluded that the racemization does not occur via a process in which the phenyl groups remain parallel but via a molecular movement in which the phenyl groups turn around each other like cog wheels.     

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.     

Synthesis and NMR conformational studies of p-tert-butyldihomooxacalix[4]-arene derivatives

Abstract

The tetramethyl (2) and tetraethyl (3) ethers, and the tetraacetate (4) derivatives of the p-tert-butyldihomooxacalix[4]arene were prepared. The mobility of these compounds studied by temperature-dependent ¹H NMR spectroscopy. For the tetraacetate derivative, at room temperature, 1,2- or 1,3-alternate conformations are suggested. Those conformations were confirmed by NOE difference and COSY spectra for the tetraethyl ether derivative in CDCl₃ at -20°C.     

Characterization of 2-phenylbenzo[g]quinoxaline derivatives as viscosity-sensitive fluorescent probes

To develop viscosity-sensitive fluorescent probes, five different substituted 2-phenylbenzo[g]quinoxaline derivatives (3a-e) were designed and synthesized by using benzo[g]quinoxaline as a fluorophore and phenyl ring bearing a rotatable single bond as a viscosity-sensitive unit. The fluorescence properties of these compounds were investigated in the media of the ethylene glycol-glycerol mixture with varied viscosity. It is found that 2-(4-hydroxyphenyl)benzo[g]quinoxaline (3d) and 2-(4-dimethylaminophenyl)-benzo[g]quinoxaline (3e) carrying stronger electron-donating groups in the phenyl ring show more sensitive fluorescence response to viscosity, revealing their potential use in viscosity detection and the key role of the substituted groups. The effects of solvent polarity and pH on the fluorescent properties of 3d and 3e were also discussed. The present study might be useful in developing viscosity-sensitive fluorescent probes.     

Synthesis of 3-phenylbenzo[c]isoxazoles by thermocyclization of 2-azidobenzophenones

3-Phenylbenzo[c]isoxazoles were synthesized by non-catalytic thermolysis of 2-azidobenzophenones in dry xylene with quantitative yields. The trace content of water in solvents reduces the yields of the reaction products. 2-Azidobenzoic acid esters are stable under the indicated conditions.

     

Synthesis of 6-fluoroalkylbenzo[h]cyclopenta[c]quinoline and -benzo[c]phenanthridine derivatives

Russian Chemical Bulletin -     

Benzocyclobutenes-x : Synthesis of cyclobuta[l]phenanthrene derivatives from [2 + 2]photoadducts of chlorinated ethenes and phenanthrene

UV irradiation of phenanthrene and 1,1-dichloro-, 1,2-dichloro-, and 1,1,2-trichloroethenes resulted m [2+2]cycloaddition to give cyclobutane derivatives. Treatment of the 1,2-dichloro-adducts with N-bromosuccinimide resulted in aromatisation to yield cis- and tras-l,2-dichloro-1,2- dihydrocyclobuta[l)phenanthrene, whereas the 1,1-dichloro-adduct resulted in aromatisation and hydrolysis to give cyclobuta[l]phenanthrene-l(2H)-one. The trichloroethene adducts gave 1,2-dichloro-2a,10b-dihydrocyclobuta [l)phenanthrene upon treatment with base, and reaction with N- bromosuccinimide resulted in bromine substitution in the cyclobutane ring. The stereochemistry of the adducts and the stereoselectivity of the bromination reactions are discussed.     

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.     

The synthesis and some reactions of 2,3-substituted 1-phenylbenzo[f]quinoline

A series of 2,3-substituted 1-phenylbenzo[f]quinolines was synthesized by the Friedlander condensation of 1-benzoyl-2-naphthylamine with β-keto esters. Some chemical transformations of these compounds and the preparation of 13H-benzo[f]indeno[2,1-c]quinoline-13-one and its 9-methyl derivative are described.     

Synthesis and conformational analysis of 1-[2,4-dideoxy-4-C-hydroxymethyl-alpha-l-lyxopyranosyl]thymine

Previously different types of nucleosides with a six-membered carbohydrate moiety have been evaluated for their potential antiviral and antibiotic properties and as building blocks in nucleic acid synthesis. However, a pyranose nucleoside with a 1,4-substitution pattern like 1-[2,4-dideoxy-4-C-hydroxymethyl-alpha-l-lyxopyranosyl]thymine (4) has not been studied yet. Modeling suggested that this nucleoside would show the (4)C(1) conformation in contrast to anhydrohexitol nucleosides (1) whose most stable conformation is (1)C(4). The key to the synthesis of 4 involves the stereoselective introduction of the hydroxymethyl group onto the C-4 carbon of the pyranose sugar. Attempts to achieve this via hydroboration/oxidation of a C-4'-exocyclic vinylic intermediate selectively yielded the undesired alpha-directed hydroxymethyl group. Therefore, we envisaged another approach in which the C-4 substituent was introduced upon treatment of 2,3-O-isopropylidene-1-O-methyl-4-O-phenoxythiocarbonyl-alpha-l-lyxopyranose with beta-tributylstannyl styrene. This allowed stereoselective beta-directed introduction of a 2-phenylethenyl group at C-4, which was converted via oxidation/reduction (OsO(4), NaIO(4)/NaBH(4)) into the desired 4-hydroxymethyl group (20). The resulting 1-O-methyl-2,3,6-tri-O-acetyl-protected sugar was coupled with silylated thymine, using SnCl(2) as Lewis acid (22). After suitable protection, Barton deoxygenation of the 2'-hydroxyl function of the obtained ribo-nucleoside yielded the desired 2'-deoxynucleoside 4, indeed showing the expected equatorial orientation of the thymine ring ((4)C(1)).     

Functionalized derivatives of dibenzo [c,j] dipyrazolo-[3,4-f∶3′,4′-m] [1,2,5,8,9,12] hexaazacyclotetradecinate

A number of derivatives of dibenzo [c,j] dipyrazolo [3,4-f3,4-m] [1,2,5,8,9,12]-hexaazacyclotetradecinate with peripheral nitro, amino, and acetylamino groups have been synthesized.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 106–114, January, 1984.     

Synthesis and conformational properties of tetranitroazacalix[4]arenes

Tetranitroazacalix[4]arenes have been synthesized by the nucleophilic aromatic substitution of 1,5-difluoro-2,4-dinitrobenzene with 1,3-diaminobenzenes. An X-ray crystal structure analysis revealed that the azacalixarenes adopt a non-symmetrical 1,3-alternate conformation, and the dinitrobenzene rings strongly conjugate with the bridging nitrogen atoms. In the ¹H NMR spectrum (CDCl₃, 30 °C), the tetraisopropyl derivative 3b displays a pair of diastereotopic methyl signals of the isopropyl groups in agreement with the frozen 1,3-alternate conformation on the NMR time scale. The free energy of activation () for the macrocyclic inversion was determined to be 87.5 kJ mol⁻¹ by temperature-dependent NMR spectroscopy.     

Synthesis of benzo[h]quinolone and benzo[c]acridinone derivatives by Fe3O4@PS-Arginine[HSO4] as an efficient magnetic nanocatalyst

Fe₃O₄ magnetic nanoparticles were synthesized and functionalized by propylsilan and after that arginine. The synthesized Fe₃O₄@PS-Arginine magnetic nanoparticles were modified to obtain Fe₃O₄@PS-Arg[HSO₄]. These nanoparticles were used as environmental friendly solidacid magnetic nanocatalyst for the synthesis of 2-amino-4-arylbenzo[h]quinoline-3-carbonitrile and 10,10-dimethyl-7-aryl-9,10,11,12-tetrahydrobenzo[c]acridin-8(7H)-one derivatives via the one-pot reaction of α-naphthilamine and aromatic aldehydes with malononitrile or dimedone. Simple operation, high reaction yields, reusability of catalyst for several times, short reaction time and easy separation from reaction mixture are the key advantages of using this catalyst.     

Synthesis and conformational evaluation of p-tert-butylthiacalix[4]arene-crowns

Bridging of p-tert-butylthiacalix[4]arene afforded 1,3-dihydroxythiacalix[4]arene-monocrown-5 (3b), 1,2-alternate thiacalix[4]arene-biscrown-4 and -5 (4a,b), and 1,3-alternate thiacalix[4]arene-biscrown-5 and -6 (5a,b), depending on the metal carbonates and oligoethylene glycol ditosylates used. Starting from 1,3-dialkylated thiacalix[4]arenes, the corresponding bridging reaction gave 1,3-alternate, partial-cone, and cone conformers 10-19, depending on the substituents present. Temperature-dependent studies revealed that the conformationally flexible 1,3-dimethoxythiacalix[4]arene-crowns 10a-c exclusively occupy the 1,3-alternate conformation. Demethylation exclusively gave the cone 1,3-dihydroxythiacalix[4]arene-crowns (3a,c), which could not be obtained by direct bridging of thiacalix[4]arene. The different structures were assigned on the basis of several X-ray crystal structures and extensive 2-D (1)H NMR studies.