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Several 15,16-epoxy-8,13,14-labdatriene derivatives modified at the C-16 position with a 1,2,4-oxadiazole ring with various substituent in the 5-th position, were obtained via multistep synthesis from 16-formyl derivatives of natural diterpenoid lambertianic acid. The cytotoxicity of furanolabdanoid-based 1,2,4-oxadiazoles was evaluated against human cancer cells (CEM-13, MT-4, U-937, MCF-7, MDA-MB-231, MEL-8) using the conventional MTT assays. All the tested diterpenoid-oxadiazole hybrids displayed better cytotoxic activity then lambertianic acid. The activity and selectivity to the cell line increased even further in the compounds containing a chloromethyl substituent in the 5-th position of the 1,2,4-oxadiazole ring. Two of the synthesized compounds exhibited high cytotoxic activity against lymphoblastoid cell line CEM-13 (GI50 0.08-0.34 μM), which was higher that than of the comparative drug Doxorubicin. The antitumor mechanism may be related to apoptosis induction in U-937, MCF-7, and CEM-13 cells.

A selective synthesis of 7‐ or 14‐nitrogen containing tricyclic diterpenoids was completed according to a strategy in which the key step was the catalyzed direct allylic amination of methyl 14α‐hydroxy‐15,16‐dihydroisopimarate with a wide variety of nitrogenated nucleophiles. It was revealed that the selectivity of the reaction depends on the nature of nucleophile. The catalyzed reaction of the mentioned diterpenoid allylic alcohol with 3‐nitroaniline, 3‐(trifluoromethyl)aniline, and 4‐(trifluoromethyl)aniline yield the subsequent 7α‐, 7β‐ and 14αnitrogen‐containing diterpenoids. The reaction with 2‐nitroaniline, 4‐nitro‐2‐chloroaniline, 4‐methoxy‐2‐nitroaniline, phenylsulfamide, or tert‐butyl carbamate proceeds with the formation of 7α‐nitrogen‐substituted diterpenoids as the main products.

1H and 13C NMR studies and quantum chemical calculations show the interaction between 2,11-dithia-5,6,8,9-tetramethyl[32](1,4)cyclophane and nitrosonium cation to result in the formation of π- and n-complexes. According to DFT/B3LYP/6-31G(2d,p) calculations, formation of nitrosonium complexes is a strongly exothermic process both in gas phase and in SO2. Affinity of single-charged complexes to NO+ is usually larger than that of double-charged and triple-charged complexes, affinity of all the charged complexes to nitrosonium cation in SO2 being larger than that in gas phase. The π-complex with nitrosonium cation coordinated to the methylated aromatic ring is the most stable with structural characteristics being close to those obtained by X-ray diffraction for nitrosonium π-complexes of hexamethylbenzene and other arenes. The N―O bond lengths in all the complexes are quite close to each other and larger than that in NO+ cation. The S―N bond length increases upon transition from single-charged to double-charged and polycharged complexes. Copyright © 2014 John Wiley & Sons, Ltd.

Several 15,16-epoxy-8,13,14-labdatriene derivatives modified at the C-16 position with a 1,2,4-oxadiazole ring with various substituent in the 5-th position, were obtained via multistep synthesis from 16-formyl derivatives of natural diterpenoid lambertianic acid. The cytotoxicity of furanolabdanoid-based 1,2,4-oxadiazoles was evaluated against human cancer cells (CEM-13, MT-4, U-937, MCF-7, MDA-MB-231, MEL-8) using the conventional MTT assays. All the tested diterpenoid-oxadiazole hybrids displayed better cytotoxic activity then lambertianic acid. The activity and selectivity to the cell line increased even further in the compounds containing a chloromethyl substituent in the 5-th position of the 1,2,4-oxadiazole ring. Two of the synthesized compounds exhibited high cytotoxic activity against lymphoblastoid cell line CEM-13 (GI50 0.08-0.34 μM), which was higher that than of the comparative drug Doxorubicin. The antitumor mechanism may be related to apoptosis induction in U-937, MCF-7, and CEM-13 cells.

Telomeres define the ends of linear eukaryotic chromosomes and are required for genome maintenance and continued cell proliferation. The extreme ends of telomeres terminate in a single-strand protrusion, termed the G-overhang, which, in vertebrates and fission yeast, is bound by evolutionarily conserved members of the POT1 (protection of telomeres) protein family. Unlike most other model organisms, the flowering plant Arabidopsis thaliana encodes two divergent POT1-like proteins. Here we show that the single-strand telomeric DNA binding activity present in A. thaliana nuclear extracts is not dependent on POT1a or POT1b proteins. Furthermore, in contrast to POT1 proteins from yeast and vertebrates, recombinant POT1a and POT1b proteins from A. thaliana, and from two additional Brassicaceae species, Arabidopsis lyrata and Brassica oleracea (cauliflower), fail to bind single-strand telomeric DNA in vitro under the conditions tested. Finally, although we detected four single-strand telomeric DNA binding activities in nuclear extracts from B. oleracea, partial purification and DNA cross-linking analysis of these complexes identified proteins that are smaller than the predicted sizes of BoPOT1a or BoPOT1b. Taken together, these data suggest that POT1 proteins are not the major single-strand telomeric DNA binding activities in A. thaliana and its close relatives, underscoring the remarkable functional divergence of POT1 proteins from plants and other eukaryotes.

POT1 is a single-copy gene in yeast and humans that encodes a single-strand telomere binding protein required for chromosome end protection and telomere length regulation. In contrast, Arabidopsis harbors multiple, divergent POT-like genes that bear signature N-terminal OB-fold motifs, but otherwise share limited sequence similarity. Here, we report that plants null for AtPOT1 show no telomere deprotection phenotype, but rather exhibit progressive loss of telomeric DNA. Genetic analysis indicates that AtPOT1 acts in the same pathway as telomerase. In vitro levels of telomerase activity in pot1 mutants are significantly reduced and are more variable than wild-type. Consistent with this observation, AtPOT1 physically associates with active telomerase particles. Although low levels of AtPOT1 can be detected at telomeres in unsynchronized cells and in cells arrested in G2, AtPOT1 binding is significantly enhanced during S-phase, when telomerase is thought to act at telomeres. Our findings indicate that AtPOT1 is a novel accessory factor for telomerase required for positive telomere length regulation, and they underscore the coordinate and extraordinarily rapid evolution of telomere proteins and the telomerase enzyme.

N-Acetylation of polyfluoroarylamines is proposed as a meansto remove the amino group blocking effect of their hydrodefluorination by zinc in aqueous ammonia. With pentafluoroacetanilide, the Zn ion specific effect has been demonstrated to be responsible for ortho hydrodefluorination. This regiochemistry is accompanied by the removal of a fluorine atom from the para position, which occurs predominantly in the initial phase of the process in the absence of deliberately added zinc salt. The CuCl2 additive has been found to accelerate the reaction and to propel it to double defluorination. Quantum chemical calculations suggest a diminished electron affinity of pentafluoroaniline, which is responsible for its inertness in relation to the hydrodefluorination reaction. The pentafluoroaniline radical anion, which essentially has a nonplanar structure, is prone to easy fragmentation to give an aminotetrafluorophenyl radical. For pentafluoroacetanilide, CVA experiments and quantum chemical calculations predict that the pentafluorophenyl moiety serves as the electron receptor and that the acetamido group is twisted out of coplanarity with the benzene ring; thus, together with the electron-withdrawing effect of the acetyl group, the amino group blocking effect is suppressed. On this ground, the selective ortho hydrodefluorination of polyfluoroacetanilides is developed as an important protocol for the expeditious and general synthesis of polyfluorobenzo azaheterocycles via readily accessible polyfluoroarylamines from base polyfluoroarenes. Its applicability has been illustrated by preparing quinolines that possess a polyfluorinated benzene moiety by the Skraup synthesis utilizing crude polyfluoroacetanilide hydrodefluorination products as starting materials. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

In contrast to thermolysis of 1,3λ4δ2,2,4-benzodithiadiazine (1) and its 5,6,7,8-tetrafluoro derivative 2 in dilute (10–3M) hydrocarbon solutions, which leads to persistent 1,2,3-benzodithiazolyls in nearly quantitative yields, the thermolysis of 1 and 2 (the 6-6 bicyclic system) in concentrated (0.5 M) solutions at 150–170 °C results in complex mixtures of various polysulfur-nitrogen heterocycles, in particular differently fused 5-5-6, 5-6-7 and 5-6-6-6 polycyclic systems that were previously unknown. The products were isolated by column chromatography, and the structures of the 5-5-6 (11, 12), 5-6-7 (5, 13), and 5-6-6-6 (6, 14, 15) polycyclic systems, as well as the 6-7 (4) and 5-6 (16) bicyclic derivatives, confirmed by X-ray diffraction. The crystal packing of 6 and 11–16 is discussed with special emphasis on π-stacking interactions. The fluorescent properties of the 5-6-6-6 systems synthesized are reported. An alternative approach to the linear 5-6-6-6 system 15 based on self-condensation of an R–N=PPh3 precursor (R = 4,5,6,7-tetrafluoro-1,2,3-benzodithiazol-2-yl) is described, and the free-radical character of this new reaction is proved. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

The existence of the orbital interaction presented in the literature as being the cause for the stabilisation of the Z,Z configuration of Ph-S-N=S= N-S-Ph (1) and its derivatives in the crystal phase, has been investigated. The results of theoretical calculations at the DFT/B3LYP/6-311+G* level of theory suggest that such a stabilising interaction might not exist or be ex- tremely weak and that packing forces must be the main cause of the observed Z,Z configuration in the solid. To reach this conclusion structural and en- ergetic parameters were combined to study the bonding in these -S-N=S=N- S- systems. For the analogous Ph-Se- N=S=N-Se-Ph (2) in particular the iso- meric equilibrium in solution found in the variable-temperature 77 Se NMR spectrum indicates that, in the gas phase or in solution, the observed Z,Z configuration is not stabilised to a greater extent than the Z,E configura- tion.

[K(18-crown-6)]+ salts of the [RNSN]− anions (R = Alk, Ar) and the [NSN]2− dianion, which are thermally stable and very soluble in aprotic organic solvents, were prepared from [K(18-crown-6)]+[tBuO]− and the corresponding R−N=S=N−SiMe3 and (Me3Si−N=)2S, respectively. The salts are characterized by multinuclear (1H, 13C, 14N, 19F, 29Si and 39K) NMR spectroscopy in solution and by X-ray diffraction in the solid state. The experimentally determined bond lengths confirm that the [RNSN]− anions are thiazylamides, R−N−−S≡N rather than sulfur diimides, R−N=S=N−. Relative to O=S=O, in the [NSN]2− dianion, which is the genuine aza-analogue of sulfur dioxide, the bond lengths are elongated and the bond angle is widened. This might reflect electrostatic repulsion between the negatively charged N atoms. The experimental results are in agreement with theoretical calculations (RHF, B3LYP, MP2). In the nitrogen NMR spectra, when going from [AlkNSN]− to [ArNSN]−, the low-field signal of the terminal (unsubstituted) N atom reveals further deshielding, whereas the high-field signal of the internal (substituted) N atom displays further shielding. The 14N NMR resonance for the [NSN]2− dianion is practically insensitive to the counterion. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The series of title compounds has been prepared through both electrophilic (C6HnF5-n N=S=N-SiMe3 + SCl2) and nucleophilic (C6HF4-S-N=S=N-SiMe3 + CsF) intramolecular ortho-cyclisation reactions, and the former route seems to be the more effective. High regioselectivity of the ring-closing procedures is observed in both cases. The compounds were characterised by X-ray crystallography and multinuclear (H-1, C-13, N-15 and F-19) NMR spectroscopy. In accordance with GIAO calculations, N-15{H-1} experiments and the effects observed on complete substitution of hydrogen by fluorine, the high-field signal in the N-15 NMR spectra can be assigned to N-4 and the low-field signal to N-2. In the crystal, 5,6,7-trifluoro- (5) and 5,6,8-trifluoro-1,3lambda(4)delta(2),2,4-benzodithiadiazine (6) are planar, whereas the 6,8-difluoro derivative 3 is bent along the S1...N4 line by 8.3degrees. According to NICS calculations the heterocycle moiety in this compound class is antiaromatic while the carbocycle is aromatic. The fluorine substituents increase the aromaticity - and in some cases (especially when a fluorine atom is present in the 8-position) the antiaromaticity - of the corresponding rings. The ortho-fluoro-containing starting material C6HnF5-n N=S=N-SiMe3 (n = 2: 10) cyclises to the fluorinated 2,1,3-benzothiadiazole 27 upon treatment with CsF instead of SCl2. For starting compound 6-HC6F4-S-N=S=N-SiMe3 (14) the planar (Z,E) configuration features a short intramolecular H...N contact, as evidenced by X-ray diffraction. Both the reaction pathways mentioned are also discussed. ((C) Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2003).

Summary The telomerase reverse transcriptase can recognize broken chromosome ends and add new telomeres de novo in a reaction termed ‘chromosome healing’. Here we investigate new telomere formation in vitro by telomerases from a variety of flowering plant species. Comparing the electrophoretic mobilities and nucleotide sequences of the products, we uncovered three different modes of new telomere formation. The soybean telomerase, designated a Class I enzyme, only elongated DNA primers ending in telomeric nucleotides. Arabidopsis and maize telomerases, designated Class II enzymes, efficiently extended completely non-telomeric sequences by positioning the 3′ terminus at a preferred site on the RNA template. Silene latifolia and sorghum telomerases constituted class III enzymes that elongated non-telomeric DNA primers by annealing them at alternative sites on the RNA template. For all enzymes, errors were prevalent during synthesis of the first two repeats, likely reflecting lateral instability of the primer 3′ terminus on the template during the initial rounds of elongation. Class III telomerases, however, were five- to 13-fold more error prone than class II, generating more mistakes in distal repeats added to the primers. This remarkable variability in enzyme–DNA interactions among plant telomerases does not reflect phylogenetic relationships, and therefore implies that the telomerase active site can evolve rapidly.

The synthesis of the title compounds 1 by1:1condensationof Ar N S N SiMe3 2withSCl2 followed by intramolecular ortho-cyclization of each (Ar N S N S Cl) intermediate is complicated by further reaction of 1 with SCl2 to give Herz salts 3. With the 2:SCl2 ratio of 2:1, the formation of by-products 3 is reduced and novel compounds 1 are accessible. With ortho-I containing starting material 2j, the parent compound 1s is obtained as the result of an unex- pected I, not H, substitution. The rate of the 1C SCl2 reaction depends upon a substituent's position, and the minor 8-R isomers 1l,p (RD Br, I) are isolated for the first time from mixtures with the major 6-R isomers due to reduced reactivity toward SCl2. The synthesized compounds 1-3 are characterized by mul- tinuclear (including nitrogen) NMR and X-ray crys- tallography. According to the X-ray diffraction data, 1j (6-Br) and 1k (7-Br) derivatives are planar, whereas 1i (5-Br) and 1l (8-Br) are bent along the S1¢¢¢N4 line by»5 - and»4 - , respectively, and the 1r (7-OCH3) de- rivative is planar in contrast to the known 5-OCH3 isomer, which possesses a significantly folded hetero

Between 1949 and 1957 Mayak Nuclear Facility located in the Chelyabinsk region released some discharges of radiochemical production wastes into the Techa River and Lake Karachay which resulted in an extensive contamination of large territories with long-lived radionuclides such as 90 Sr, 137 Cs, 239 Pu. Between 1994 and 1996 our research team conducted both the chromosome analysis and the electron-spin resonance (ESR) spectrometry of tooth enamel in the radiation-exposed residents of four settlements in the Techa basin. We observed significantly increased levels of chromosome aberrations in the radiation-exposed residents as compared to the controls. The ESR signal intensity and the chromosome aberration frequency in lymphocytes of the tooth donors showed a good correlation. Moreover, there was a good correlation between the level of whole-body 90 Sr activity detected by human radiation counter (HRC) and the frequency of chromosome aberrations among the radiation-exposed residents. The data showed that 15% of the inhabitants of the Muslyumovo settlement received a radiation dose exceeding 100 cGy. A large increase of chromosome damage was observed in the people born between 1949 and 1957. Therefore, the accidents at Mayak Nuclear Facility (MNF) caused the serious radionuclide contamination of the Chelyabinsk region. We suppose that radionuclides incorporated in the body, particularly, in the bone marrow are responsible for the chromosome aberrations in the inhabitants.

A homogeneous glutamyl endopeptidase splitting peptide bonds of glutamic, rarely of aspartic acid residues in peptides and proteins, was isolated from Bacillus intermedius 3-19 culture filtrate using chromatography on CM cellulose and Mono S. The enzyme molecular mass is equal to 29 kDa, pI 8.4. The protease is inhibited by diisopropylfluorophosphate. The enzyme, like other glutamyl endopeptidases, reveals two pH optima at pH 7.5 and 9.0 for casein and one at pH 8.0 for Z-Glu-pNA hydrolysis. A 6 mM K m is found for hydrolysis of the latter substrate. The enzyme activity optimum lies at 55°C, and it is stable at pH 6.5–11.0. Its N-terminal sequence shows 56% coinciding residues when compared with that of Bacillus licheniformis glutamyl endopeptidase. © 1997 Federation of European Biochemical Societies.

The 14π-electron title compound 7 has been synthesized by two different ring-closure approaches. Its structure has been determined by X-ray diffraction to be planar within ±0.018 A. The He(I) photoelectron spectrum of the title compound is assigned by Koopmans' correlation with PM3 eigenvalues based on the structural data, and by the π-perfluoro effect observed. The π-system can be rationalized y heteroatom first-order perturbation, which reduces the cycli π-delocalization. Replacement of the four fluorine substituents by hydrogen affects neither the long-wavelength absorption band in the UV/Vis spectrum nor the δ15N shift in the 15N-NMR spectrum. The synthesis of 20π-electron heterocycles related to the title compound has been attempted.

Substituted salicylaldehydes (I) react with ethyl diazoacetate (II) to give benzofuran derivatives of type (III).

The title reaction is highly regioselective, leading in both cases to 4,5,6,7,8,9-hexafluoronaphtho[1,2-c]-[1,2,5]thiadiazole (whose struture is confirmed by X-ray structure analysis) and 4,5,6,7,8,9-hexafluoronaphtho[2,3-c][1,2,5]thiadiazole in ∼94 : 6 ratio. The preferred direction of cyclization is consistent with final product thermodynamics as well as factors of kinetic control for orbital-controlled reactions (calculated by use of frontier MOs theory).

The data obtained on the regioselectivity of amination are interpreted in terms of DFT/PBE/3Z quantum-chemical calculations.

Title compounds [(VI), (VIII), and (X)] are synthesized starting from harmine (I) via quaternized derivatives (V).

An L-proline-catalyzed regioselective [4+2] cycloaddition of coumarin-3-carboxylic acids (III) to furan (IV) gives access to benzo[c]chromene derivatives (V).

Polyfluorinated di-and triarylpyrazolines were synthesized by the reactions of polyfluorinated chalcones with hydrazine hydrate and phenylhydrazine, respectively. Reactions of benzyl-idenepolyfluoroacetophenones with phenylhydrazine resulted in the mixtures of isomeric 1,5-diphenyl-3-polyfluoroaryl-and 1,3-diphenyl-5-polyfluoroarylpyrazolines. Fluorescence properties of the synthesized triarylpyrazolines were studied.

1H, 13C, and 15N NMR studies, including the use of the 13C NMR deuterium perturbation method, showed that the interaction between naphthalene or its methylated derivatives and the nitrosonium cation result in the formation of π-complexes. The chemical behaviour of these complexes was investigated; in particular, their ability to be converted into binaphthyl derivatives was established.

13C, 14N and 7Li NMR spectra of a lithiation product of the cyclic aldonitrone 1,2,2,5,5-pentamethyl-3-imidazoline 3-oxide were obtained. The 13C NMR spectrum of the lithiated particle exhibits the resonances of the C-4 and C-5 atoms (δ213 ppm and 73 ppm, respectively) shifted to high frequency relative to the signals of the corresponding nuclei of the starting nitrone (δC-4 132 ppm and δC-5 60 ppm). The 14N NMR spectrum of the particle shows the resonance of the N-3 atom (−115 ppm) at lower frequency in comparison with −74 ppm for the starting nitrone. The calculated chemical shift changes are in good agreement with those observed experimentally. The electronic structure of the lithiated particle is discussed. Copyright © 2001 John Wiley & Sons, Ltd.

A Kuganak montmorillonite that contains relatively high amount of TiO2 is used as catalyst for the Michael addition.