The synthesis of piperidine nucleoside analogs—a comparison of several methods to access the introduction of nucleobases

This work deals with the synthesis of piperidine and hydroxypiperidine analogs of nucleosides. Starting from commercially available 3-hydroxypiperidine, proline or 4-hydroxyproline, a series of piperidine derivatives of both purine and pyrimidine nucleobases was prepared. Various methods of nucleobase attachment were evaluated. The prepared compounds were tested for cytostatic, antibacterial, and antiviral properties but no significant activity was found.     

1,4-Additions of electron-rich heterocycles onto β-perfluoroalkyl enones

β-(Trifluoromethyl) enones, easily obtained in few steps from commercially available methyl hemiketal of trifluoroacetaldehyde, react with electron-rich O- and N-containing heterocycles (furans and benzofurans, pyrroles and indoles, hydroxycoumarins), through a 1,4 addition, to give heterocycles bearing a functionalized side-chain. β-(chlorodifluoromethyl)enones and β-(pentafluoroethyl)enones behave in the same way.     

Face-Centered and Volume-Centered Discrete Analogs of the Exterior Differential Equations Governing Porous Medium Flow II: Examples

This paper exemplifies discrete analogs obtained by transformation of the continuum equations governing porous media flow to a system of algebraic equations. To give insight in the underlying physics, the numerical examples are worked out algebraically. The volume-centered approximation turns out to be a reasonable simplification of the algebraically exact face-centered method.     

Rapid access to novel 2-alkylthiopyrimidine derivatives and attempt of their Tacrine analogs synthesis

A variety of novel 2-alkylthiopyrimidines were synthesized through simple condensation of arylidenemalononitriles with different 2-alkylthiouronium halide derivatives catalyzed by anhydrous potassium carbonate (K₂CO₃). The reactions have been carried out under mild conditions in i-PrOH, and the products were obtained in moderate to good yields with a simple work-up method. Subsequently, some examples of these compounds have been converted into Tacrine analogs by applying the Friedländer reaction.     

d-Orbital Reconstructions Forced by Double Bow-Shaped Deformations and Second Coordination Sphere Effects of Cu(II) Heme Analogs in HER**

Both geometric architecture and electronic configurations of heme proteins contribute to its activity. In this work we designed and synthesized a series of four copper(II) porphyrin complexes ( 4 -, 3 -, 2 - and 1 -Cu) where the molecular conformations are modulated by a pair of stepwise shortened straps on the same porphyrin side (cis-ortho) to give double bow-shaped skeletons. Single crystal structures demonstrate that the straps gradually increase the saddle deformation and the deviation of the metal centers, which is in accordance with two, unusual d-orbital reconstructions of two different ground states, as revealed by 4 K EPR and DFT calculations. In the study of the electrocatalytic hydrogen evolution reaction (HER), 1 -Cu, with the shortest straps, showed the most apparent improvement of activity. Second coordination sphere (SCS) effects created by the double bow-shaped architecture and the strong saddle porphyrin core in 1 -Cu are found to play key roles in proton trapping during the catalytic process. The work contributes a novel strategy to improve the catalytic performance of heme analogs through ligand geometric modulation.     

Expanded Analogs of Three-Dimensional Lead-Halide Hybrid Perovskites

Replacing the Pb−X octahedral building unit of A^IPbX₃ perovskites (X=halide) with a pair of edge-sharing Pb−X octahedra affords the expanded perovskite analogs: A^IIPb₂X₆. We report seven members of this new family of materials. In 3D hybrid perovskites, orbitals from the organic molecules do not participate in the band edges. In contrast, the more spacious inorganic sublattice of the expanded analogs accommodates larger pyrazinium-based cations with low-lying π* orbitals that form the conduction band, substantially decreasing the band gap of the expanded lattice. The molecular nature of the conduction band allows us to electronically dope the materials by reducing the organic molecules. By synthesizing derivatives with A^II=pyridinium and ammonium, we can isolate the contributions of the pyrazinium-based orbitals in the band gap transition of A^IIPb₂X₆. The organic-molecule-based conduction band and the inorganic-ion-based valence band provide an unusual electronic platform with localized states for electrons and more disperse bands for holes upon optical or thermal excitation.     

Synthesis and photophysical properties of azuleno[1′,2′:4,5]pyrrolo[2,1-b]quinazoline-6,14-diones: Azulene analogs of tryptanthrin

Azulene analog of tryptanthrin, azuleno[1′,2′:4,5]pyrrolo[2,1-b]quinazoline-6,14-dione, was successfully prepared by the condensation reaction of azuleno[2,1-b]pyrrole-2,3-dione with isatoic anhydride in the presence of sodium hydride or diisopropylethylamine (DIPEA). Its 2-halo derivatives were also obtained in high yields by the condensation reaction with 5-haloisatoic anhydrides in the presence of DIPEA. Reactivity toward electrophilic reagents was revealed by halogenation with N-bromosuccinimide (NBS) or N-iodosuccinimide (NIS) to afford 12-halo derivatives in high yields. Among the halo derivatives, 2-iodo and 12-iodo derivatives were reactive enough to afford phenylethynyl derivatives under Pd-catalyzed Sonogashira cross-coupling conditions. Within the phenylethynyl derivatives, only 12-phenylethynyl derivative was transformed into its 1,1,4,4-tetracyanobutadiene (TCBD) derivative by the reaction with TCNE. Amphoteric redox properties of the novel azulene analogs of tryptanthrin were characterized by spectroscopic and voltammetric analyses.     

Platinum(IV) complexes with purine analogs. Studies of molecular structure and antiproliferative activity in vitro

A series of tetrachloride platinum(IV) compounds of the general formulae PtCl₄L₂, where L = 1,2,4-triazolo[1,5-a]pyrimidine (tp) (1), 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine (dmtp) (2), 5,7-ditertbutyl-1,2,4-triazolo[1,5-a]pyrimidine (dbtp) (3) and 5-methyl-1,2,4-triazolo[1,5-a]pyrimidin-7(4H)-one (HmtpO) (4) have been prepared and characterized by thermal analysis, ¹H, ¹³C, ¹⁵N, ¹⁹⁵Pt NMR and IR spectroscopy. Spectral data suggest that the triazolopyrimidines act as a monodentate ligand via the nitrogen atom N(3). The preliminary assessments of antitumor properties of the four complexes were evaluated as in vitro antiproliferative activity against three cell lines: HL-60 human acute promyelocytic leukemia, SW707 rectal adenocarcinoma and HCV29T bladder cancer. PtCl₄(dbtp)₂ exhibits high cytotoxic activity against all human cell lines, whereas the other complexes are only moderately active.