A novel metal-binding mode of thymine nucleobases: N3 and O4 chelation

The syntheses and crystal structures of the first examples of an anionic 1-methylthymine [deprotonated at the endocyclic NH group N(3)] acting as a chelating ligand for the cis-Pd(C6F3H2)2 and cis-Pd(C6F5)2 moieties through N(3) and O(4) are reported.     

Using supercritical fluid chromatography to determine diffusion coefficients of 1,2-diethylbenzene, 1,4-diethylbenzene, 5-tert-butyl-m-xylene and phenylacetylene in supercritical carbon dioxide

The binary diffusion of 1,2-diethylbenzene, 1,4-diethylbenzene, 5-tert-butyl-m-xylene and phenylacetylene at infinite dilution in supercritical carbon dioxide were measured between 15.0 and 35.0 MPa and in the temperature range of 313.16 to 333.16K by the Taylor-Aris chromatographic method. The effect of temperature, pressure, viscosity and density was discussed. In the case of temperature dependence, additional measurements were done for 5-tert-butyl-m-xylene from 308.16 to 398.16K at 35.0 MPa. The measured diffusivities of the four solutes were compared with the calculated ones by several predictive formulas.     

Synthesis and antiproliferative activity of a C,N-cycloplatinated(II) complex with a potentially intercalative anthraquinone pendant

The synthesis of the novel anthraquinone platinum derivate [Pt(ppy)Cl(1C3)] (2) [Hppy = N,C-chelating 2-phenylpyridine; 1C3 = 1-[(3-aminopropyl)amino]-anthracene-9,10-dione] and its values of IC(50) against a panel of human tumor cell lines representative of ovarian (A2780 and A2780cisR) and breast cancers (T47D) are reported. At 24 h incubation time, complex 2 was more active than cisplatin (about 9-fold) and the free ligand 1C3 (about 2-fold) in T47-D. The observation that the cisplatin IC(50) falls by about 10-fold from 24 to 72 h, whereas that for 2 changes little, suggests substantial differences in the mode of action. Complex 2 also showed high cytotoxicity against A2780 (about 3-fold greater than cisplatin at 24 h). On the other hand, very low resistance factors (RF) of 2 in A2780cisR at 24-72 h (RF = 1.3) were observed. The interaction of 2 with DNA was followed by electrophoretic mobility and UV-visible spectroscopy, and its reaction with the model nucleobase 9-EtG was studied by (1)H NMR and ESI-MS. Theoretical calculations at the B3LYP/def2-TZVPP//BP86/def2-TZVP level of theory on complex 2 show a labile Pt-Cl bond that allows easy replacement of Cl by N-nucleophiles such as 9-EtG, which forms a stronger Pt-N bond.     

Excited-state interactions in diastereomeric flurbiprofen-thymine dyads

Excited-state interactions between (S)- or (R)-flurbiprofen ((S)- or (R)-FBP) and thymidine (dThd) covalently linked in dyads 1 or 2 have been investigated. In both dyads, the only emitting species is (1)FBP*, but with a lower fluorescence quantum yield (?(F)) and a shorter fluorescence lifetime (τ(F)) than when free in solution. These results indicate that dynamic quenching occurs either by electron transfer or via exciplex formation, with FBP as the charge-donating species. In acetonitrile, both mechanisms are favored, while in dioxane exciplex formation is predominating. Isomer 1 displays lower values of ?(F) and τ(F) than its analogue 2, indicating that the relative spatial arrangement of the chromophores plays a significant role. The triplet quantum yields (?(T)) of 1 and 2 are significantly higher than the expectations based solely on (1)FBP*-dThd intersystem crossing quantum yields (?(ISC)), with ?(T) (1) > ?(T) (2). This can be explained in terms of intramolecular charge recombination at the radical ion pairs and/or the exciplexes, which would be again dependent on geometrical factors. The triplet lifetimes (τ(T)) of (3)FBP*-dThd and free (3)FBP* are similar, indicating the lack of excited-state interactions at this stage. The FBP-dThd dyads could, in principle, constitute appropriate model systems for the elucidation of the excited-state interactions in noncovalent DNA-ligand complexes.     

Triplet excimers of fluoroquinolones in aqueous media

Generation of triplet eximers of 6-fluoro-7-piperazinyl-quinolone-3-carboxylic acids (FQs) have been detected in aqueous media using laser flash photolysis (LFP). These transient species (SS) are generated by self-quenching reactions of FQ triplet excited states such as pefloxacin (PFX), norfloxacin (NFX), the N-acetylated form of NFX (ANFX), and its methyl ester (EANFX) with their ground states. In this context, self-quenching rate constants in the range of (1-7) × 10(8) M(-1) s(-1) were determined. The triplet excimers show transient absorption spectra with λ(max) ca. 710 nm for SS(NFX), 740 nm for SS(PFX), and 620 nm for SS(ANFX) and E(ANFX), which are red-shifted with respect to their predecessors triplet excited states. These excimers can be also observed in the presence of phosphate buffer (PB). Experiments performed with NFX and ANFX at different PB concentrations showed that deprotonation processes are not involved in the generation of SS. The triplet multiplicity of the FQ excimers was confirmed by energy transfer reactions with naproxen. The correlation between fluorescence, intersystem crossing, excimer and photodegradation quantum yields of (A)NFX indicated that FQ self-quenching reactions are mainly a deactivation pathway. On the other hand, generation of FQ radical anions absorbing at λ(max) ca. 620 nm has been observed by an efficient electron transfer reaction from Trp to NFX, PFX, and ANFX (rate constants ca. 1 × 10(9) M(-1) s(-1)).     

General diastereoselective synthetic approach toward isospongian diterpenes. Synthesis of (-)-marginatafuran, (-)-marginatone, and (-)-20-acetoxymarginatone

This work describes a synthetic approach to the carbocyclic skeleton of isospongian diterpenes that uses the commercially available monoterpene (S)-carvone as a C-ring synthon, which is incorporated into the tetracyclic isospongian framework via a C→ABC→ABCD ring annulation strategy using intramolecular Diels-Alder and ring-closing metathesis reactions. This approach has been successfully used to prepare both the title natural isospongians and several nonnatural oxygenated analogues. A preliminary evaluation of the inhibitory activity of the small collection of synthesized isospongians on the mammalian mitochondrial respiratory chain revealed that most were able to inhibit the integrated electron transfer chain (NADH oxidase activity) in the micromolar range.     

Power Subgroups of Pro-(Finite Soluble) Groups

The aim of this paper is to prove that Gⁿ, the subgroup generatedby all nth-powers of a pro-(finite soluble of bounded Fittingheight) group G is a closed subgroup of G     

Reactivity of hydroxo palladium and platinum complexes towards N-substituted salicylaldimines and β-ketoimines

The binuclear hydroxo complexes [{M(C6F5)2(OH)}2]2–(M=PdandPt)reactwithN-substituted salicylaldimines (HSal=NR) or -ketoimines (RN=CMeCH2COR) to give the corresponding N-substituted salicylaldiminato or -ketoiminato mononuclear complexes, [M(C6F5)2(Sal=NR)]– (M=Pd or Pt; R= Me, Et, Ph, o-MeC6H4, p-MeC6H4 or p-ClC6H4) or [(C6F5)2M{N(R)C(CH3)CHC(O)R}]– (M=Pd or Pt; R=o-MeC6H4 or p-MeC6H4; R=Me or Ph), respectively. The complexes have been characterized by partial elemental analyses, conductance measurements and spectroscopic (i.r. and 1H and 19F- n.m.r.) methods.