Molecular dosimetry of 8-MOP + UVA-induced DNA photoadducts in Saccharomyces cerevisiae: correlation of lesions number with genotoxic potential

Acid hydrolysis of purified DNA extracted from cells of a haploid repair-proficient (RAD) yeast strain that had been treated with 8-MOP + UVA revealed the existence of two major and one minor thymine photoproduct. At survival levels of the RAD strain between 100% and 1% furanside monoadducts constituted the major DNA lesion, followed by diadducts that, at the lowest survival level, nearly reached 50% of the thymine photoproducts; pyrone-side monoadducts were only detectable at the highest UVA exposure dose applied and clearly constitute a minority photoproduct. The number of induced diadducts was verified by determination of interstrand cross-links via denaturation and renaturation of 8-MOP + UVA-treated DNA from RAD and rad2 yeast strain. 8-MOP + UVA was shown to induce two types of locus-specific mutations: reversion of the lys1-1 ochre allele was between 20- to 50-fold higher than that of the his4-38 frameshift allele. Mutant yield for the lys 1-1 reversion was the same in RAD and excision repair-deficient rad2-20 strains whereas frameshift mutagenesis was about eightfold higher in the rad2-20 background.     

UVA-induced binding of 8-methoxypsoralen to cells of Saccharomyces cerevisiae: separation and characterization of DNA photoadducts

We present methods for the determination of UVA-induced binding of 8-methoxypsoralen (8-MOP) to nucleic acids and protein and for a quantitative assay of radioactively labelled 8-MOP plus UVA induced DNA photoproducts in the yeast Saccharomyces cerevisiae. For the dose range up to 60 kJ m-2, with a wild-type survival of 1% or higher, binding to DNA is 100-fold and to RNA 10- to 20-fold more efficient than that to protein. Between 20% and 65% of the 8-MOP binds to macromolecules that are neither nucleic acids nor protein. The number of DNA-bound 8-MOP molecules for the haploid genome rises from 14 (unirradiated control) to 349 at the highest UVA exposure dose (60 kJ m-2). Gel chromatography reveals three types of DNA thymine photoproduct, the pyrone-side monoadducts, the furan-side monoadducts and the diadducts. Among these, pyrone-side monoadducts always constitute the smallest fraction, regardless of whether the treatment is with in vitro or in vivo 8-MOP plus UVA.     

Photoreaction of [Ru(hat)2phen]2+ with guanosine-5'-monophosphate and DNA: formation of new types of photoadducts

[Ru(hat)2phen]2+ (HAT=1,4,5,8,9,12-hexaazatriphenylene, phen=1,10-phenanthroline) interacts with a good affinity with polynucleotides and DNA by intercalation, despite the presence of a second voluminous ancillary HAT ligand. It photoreacts with guanosine-5'-monophosphate (GMP). From HPLC, ESMS and NMR analyses, it can be concluded that this complex forms photoadducts with GMP. In contrast to the photoadducts isolated with Ru-TAP complexes (TAP=1,4,5,8-tetraazaphenanthrene), the photoadducts with [Ru(hat)2phen]2+ contain a covalent link between the oxygen atom of the guanine unit and a HAT ligand. Formation of oxidised photoadducts and compounds resulting from the addition of two GMP entities to the complex are also detected as side products. In the presence of oligo- and polynucleotides, [Ru(hat)2phen]2+ yields photoadducts when guanine bases are present.     

A new synthetic approach to the lactol moiety of halichoblelide

A stereoselective approach to the γ-lactol moiety of halichoblelide is described starting from commercially available (R)-3-butyn-2-ol. The key step is the hydroboration of a chiral protected 1,2-butadien-3-ol and its addition to furfural.     

Preparation of C8-amine and acetylamine adducts of 2'-deoxyguanosine suitably protected for DNA synthesis

[reaction: see text] C8-Amine and acetylamine adducts of 2'-deoxyguanosine were synthesized. Our approach provides solutions for the coupling of aromatic amines to a protected 8-bromo-2'-deoxyguanosine derivative, for the selective acetylation of the coupled adduct at N(8) and for a protecting group scheme preserving the integrity of the base-labile N(8) acetyl group during DNA synthesis.     

Synthesis and characterization of some new S-alkylated and mannich bases carrying 2-thioxoimidazolidin-4-one moiety

Russian Journal of General Chemistry - In the present study two new series of 4-[4-(3-hydroxypropoxy)-3-methoxybenzylidene]-1-(3-chlorophenyl)-2-(alkylthio)-1H-imidazol-5(4H)-ones and...     

A new class of CVD precursors to metal borides: Cr(B3H8)2 and related octahydrotriborate complexes

Treatment of CrCl3 with sodium octahydrotriborate, NaB3H8, affords a thermally unstable purple liquid thought to be a chromium(III) hydride of stoichiometry CrH(B3H8)2. This hydride converts rapidly at room temperature to the chromium(II) complex Cr(B3H8)2, which adopts a square-planar structure in which four hydrogen atoms form the coordination sphere of the chromium atom. This chromium(II) species forms six-coordinate Lewis base adducts Cr(B3H8)2L2, where L is Et2O, thf, or PMe3; the first two of these adopt trans geometries, whereas the latter is cis. Volatile Cr(B3H8)2 is the first homoleptic transition metal complex of the octahydrotriborate anion, and it readily forms CrB2 thin films by CVD at 250 degrees C.     

A new class of (mu-eta2:eta2-disulfido)dicopper complexes: synthesis, characterization, and disulfido exchange

Rare examples of (mu-eta2:eta2-disulfido)dicopper complexes have been prepared from Cu(I) and Cu(II) complexes of beta-diketiminate and anilido-imine supporting ligands. A novel byproduct derived from sulfur functionalization of the methine position of a beta-diketiminate ligand was identified. DFT calculations on [(LCu)2X2] (L = beta-diketiminate, X = O or S) complexes rationalize the absence of a bis(mu-sulfido)dicopper isomer, [Cu2(mu-S)2](2+), in the synthetic reactions, yet predict that a [Cu2(mu-S)2](0) core is a stable product of 2-electron reduction of the [Cu2(mu-eta2:eta2-S2)](2+) unit. Exchange of the disulfido ligand was discovered upon reaction of a (mu-eta2:eta2-disulfido)dicopper complex with a Cu(I) reagent.     

Synthesis and characterization of the homoleptic octahydrotriborate complex Cr(B3H8)2 and its Lewis base adducts

Solvate-free sodium octahydrotriborate, NaB3H8, is prepared on a 20 gram scale from sodium amalgam and diborane in diethyl ether. This substance, which is chemically related to borohydride-based compounds being investigated as hydrogen storage materials, is also useful for the preparation of transition-metal complexes bearing B3H8 ligands. Treatment of CrCl3 with NaB3H8 affords a thermally unstable purple liquid thought to be a chromium(III) hydride of stoichiometry CrH(B3H8)2. This hydride converts rapidly at room temperature to the chromium(II) complex Cr(B3H8)2, which adopts a square-planar structure in which four hydrogen atoms form the coordination sphere of the chromium atom. This chromium(II) species forms six-coordinate Lewis base adducts Cr(B3H8)2L2, where L is Et2O, THF, or PMe3; the first two of these adopt trans geometries, whereas the latter is cis. Volatile Cr(B3H8)2 is the first homoleptic transition-metal complex of the octahydrotriborate anion, and it is an excellent single-source precursor for the chemical vapor deposition of thin films of CrB2 at temperatures as low as 200 degrees C. Crystal structures of the new complexes are reported.     

Diels-Alder adducts of 4-chloro-1,6-dihydrophosphinine derivatives: A new precursor of 2-phosphapropene

The 4-chloro-1,6-dihydrophosphinine derivatives, prepared as a mixture of 3- and 5-methyl isomers from the thermolysis of dichlorocarbene adducts with 1-R-3-methylphospholene oxide (R  Me, MeO, EtO, n-PrO, i-PrO), participate in Diels-Alder reactions with dimethyl acetylenedicarboxylate and N-phenylmaleimide. The former reactant is of special value since the 2-phosphabicyclo[2.2.2]octa-5,7-diene framework is thermally labile and undergoes retrocycloaddition by a different path, eliminating the C P bridging unit as a low-coordinate species. Thus, in the case of R  Me, the initial phosphine oxides (a mixture of isomers) have been reduced to the phosphines and these undergo straightforward fragmentations on heating at 50°C to produce 2-phosphapropene. The reactions of this transient species with water and alcohols have been investigated. Unlike the case of stabilized phosphaalkenes, hydration occurs smoothly without catalysis to produce Me₂P(O)H; addition of alcohols gives phosphinites, Me₂POR. The structure of the Diels-Alder adducts was confirmed by ³¹P, ¹H, and ¹³C NMR spectroscopy. Each of the isomeric 1,6-dihydrophosphinine oxides gives two diastereomeric adducts; partial separation of some of the resulting four-component mixtures was achieved with silica gel chromatography.     

Synthesis and spectroscopic characterization of new Schiff bases containing the benzo-15-crown-5 moiety

New crown ether Schiff base derivatives were prepared by the condensation of 4'-formylbenzo-15-crown-5 or 4'-formyl-5'-hydroxybenzo-15-crown-5 with 1,2-bis(2-aminophenoxy)ethane. The structures of these new compounds were confirmed on the basis of elemental analysis, IR, (1)H- and (13)C-NMR, UV-Vis and mass spectroscopic data.     

Extension of the electrostatic-covalent model to 2:1 adducts

An extension to the Electrostatic-Covalent model is proposed for the prediction of physicochemical properties and enthalpies of interaction for two donor molecules reacting with a single acceptor molecule. The coordination of the first base modifies the acceptor tendencies for binding a second base. Each different base forms a different acceptor for coordinating the second base, so in any model different acceptor parameters are required for the second step for each base. An E and C based model is derived to reflect this behavior and is applied to several 2:1 adducts providing a new interpretation of their reactivity. Literature correlations of 2:1 adducts which use a single average acceptor parameter for the sum of the two steps do not reflect this behavior so the meaning of the fit and the resulting parameters are not clear. Furthermore, since an average does not reflect a different acceptor parameter in the second step for each base the cause of deviations in such a fit is not clear. The model is extended to encompass reactivity of bidentate phosphines. Donor parameters are reported for the first coordination step of bidentate phosphines. The second step of bidentate donor binding is affected by the strength of the acceptor interaction in the first step. Equations are derived to correlate the total enthalpies of reaction of bidentate phosphines. Some generalizations concerning reactivity can be made but limited data precludes a thorough evaluation of the model.     

One-electron oxidation of the guanine moiety of 2'-deoxyguanosine: influence of 8-oxo-7,8-dihydro-2'-deoxyguanosine

The influence of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) on riboflavin and UVA-mediated one-electron oxidation of an aqueous aerated solution of 2'-deoxyguanosine (dGuo) has been studied. Using labeled experiments, we have demonstrated that, despite not being able to detect significant amounts of 8-oxodGuo upon one-electron oxidation of dGuo, 8-oxodGuo is indeed produced but is further rapidly degraded to oxidized nucleosides. Evidence is provided showing that an efficient electron transfer reaction from 8-oxodGuo to the guanine radical cation or rather its deprotonated form occurs, giving rise to the specific decomposition of 8-oxodGuo together with the restitution of dGuo. It could be concluded that 8-oxodGuo efficiently protects dGuo from decomposition by the one-electron oxidation reaction.     

A new access to substituted tetraethyl N-Boc 2-aminoethylidene-1,1-bisphosphonates and phosphonyl-substituted aza-Morita-Baylis-Hillman-type adducts

A general one-pot synthesis of substituted 2-aminoethylidene-1,1-bisphosphonates has been developed. The protocol involves base-induced addition of sodium tetraethyl methylenebisphosphonate to N-Boc imines generated in situ from N-Boc-α-amidoalkyl-p-tolylsulfones by the action of sodium hydride. The direct and efficient conversion of the title compounds into aza-Morita-Baylis-Hillman-type adducts has been also elaborated.     

A new class of chiral organogermanes derived from C2-symmetric dithiols: synthesis,characterization and stereoselective free radical reactions

A new class of dithiostannanes and dithiogermanes have been prepared from 1,1'-binaphthyl-2,2'-dithiol and 3,3'-bis(trimethylsilyl)-1,1'-binaphtho-2,2'-dithiol. While reduction of 4-butyl-4-chloro-3,5-dithia-4-stanna-cyclohepta[2,1-a;3,4-a']dinaphthalene to the corresponding tin hydride was unsuccessful, 4-tert-butyl-3,5-dithia-4-germa-cyclohepta[2,1-a;3,4-a']dinaphthalene and 4-tert-butyl-2,6-bis(trimethylsilyl)-3,5-dithia-4-germa-cyclohepta[2,1-a;3,4-a']dinaphthalene were obtained by reduction of the parent germanium chlorides with NaBH(4) and LiBH(4), respectively. Kinetic constants for hydrogen transfer to a primary alkyl radical were measured for both germanium hydrides. Reduction of alpha-halo carbonyl compounds by these germanium hydrides occurs with moderate ee values (up to 42%), while hydrogermylation of methyl methacrylate occurs with low selectivity (<3/1) for the former hydride but high selectivity (>10/1) for the latter.     

Differential survival of Escherichia coli uvrA,uvrB, and uvrC mutants to psoralen plus UV-A (PUVA): Evidence for uncoupled action of nucleotide excision repair to process DNA adducts

The nucleotide excision repair mechanism (NER) of Escherichia coli is responsible for the recognition and elimination of more than twenty different DNA lesions. Herein, we evaluated the in vivo role of NER in the repair of DNA adducts generated by psoralens (mono- or bi-functional) and UV-A light (PUVA) in E. coli. Cultures of wild-type E. coli K12 and mutants for uvrA, uvrB, uvrC or uvrAC genes were treated with PUVA and cell survival was determined. In parallel, kinetics of DNA repair was also evaluated by the comparison of DNA sedimentation profiles in all the strains after PUVA treatment. The uvrB mutant was more sensitive to PUVA treatment than all the other uvr mutant strains. Wild-type strain, and uvrA and uvrC mutants were able to repair PUVA-induced lesions, as seen by DNA sedimentation profiles, while the uvrB mutant was unable to repair the lesions. In addition, a quadruple fpg nth xth nfo mutant was unable to nick PUVA-treated DNA when the crude cell-free extract was used to perform plasmid nicking. These data suggest that DNA repair of PUVA-induced lesions may require base excision repair functions, despite proficient UvrABC activity. These results point to a specific role for UvrB protein in the repair of psoralen adducts, which appear to be independent of UvrA or UvrC proteins, as described for the classical UvrABC endonuclease mechanism.     

Synthesis,characterization and pharmacological evaluation of some new 1,3,4-oxadiazole derivatives bearing 3-chloro-2-fluoro phenyl moiety

A new series of 2-(3-chloro-2-fluorophenyl)-5-aryl-1,3,4-oxadiazole (3a–j) and 2-(aryl sulfanyl)-5-(3-chloro-2-fluorophenyl)-1,3,4-oxadiazole (5a–e) were synthesized via a multistep reaction from 3-chloro-2-fluoro benzoic acid. The newly synthesized compounds were characterized by IR, ¹H NMR, ¹³C NMR, mass spectral data and elemental analysis. They were also screened for their in vivo anti-convulsant and anti-inflammatory activities. Some of them exhibited significant biological activities and were well supported by in silico molecular docking studies for the inhibition of cyclooxygenase-2 (PDB ID: 1CX2) and voltage-gated sodium channels (PDB ID: 4F4L) comparable with the standard drugs. Thus, they were believed to be good inhibitors of cyclooxygenase-2 (PDB ID: 1CX2) and voltage-gated sodium channels (PDB ID: 4F4L).     

Preparation and characterization of new glassy system As2P2S8-Ga2S3

Glasses having the composition (100 - x)As2P2S8-xGa2S3 with x ranging from 0 to 50% were investigated to determine the compositional effect on properties and local structure. The glass transition temperature (Tg) and the stability parameter against crystallization (Tx - Tg) increased with the addition of Ga2S3. The structure of these glasses was probed by Raman scattering, Fourier transform infrared (FT-IR) and 31P nuclear magnetic resonance. On the basis of the observed vibrations and the strength of the 31P-31P homonuclear magnetic dipolar coupling, two scenarios can be proposed for the structural evolution induced by the addition of Ga2S3. For x or= 30% we have depolymerization of the As2P2S8 units and the formation of a network of GaPS4 units with each PS 4/2 unit (Q4) species carrying a single positive formal charge.