Synthesis and chemistry of some pyridazine nucleosides related to certain 5-substituted pyrimidine nucleosides

Condensation of 3,4-dichloro-6-[(trimethylsilyl)oxy] pyridazine ( 3 ) with 1-O-acetyl-2,3,5-tri-O-benzoyl-β- D -ribofuranose ( 4 ), by the stannic chloride catalyzed procedure, has furnished 3,4-dichloro-1-(2,3,5-tri-O-benzoyl-β- D -ribofuranosyl) pyridazin-6-one ( 5 ). Nucleophilic displacement of the chloro groups and removal of the benzoyl blocking groups from 5 has furnished 3-chloro-4-methoxy-, 3,4-dimethoxy-, 4-amino-3-chloro-, 3-chloro-4-methylamino-, 3-chloro-4-hydroxy-, and 4-hydroxy-3-methoxy-1-β- D -ribofuranosylpyridazin-6-one. An unusual reaction of 5 with dimethylamine is reported. Condensation of 4,5-dichloro-3-nitro-6-[(trimethylsilyl)oxy]pyridazine with 4 yielded 4,5-dichloro-3-nitro-1-(2,3,5-tri-O-benzoyl-β- D -ribofuranosyl)pyridazin-6-one ( 24 ). Nucleophilic displacement of the aromatic nitro groups from 24 is discussed. Condensation of 3 with 3,5-di-O-p-toluoyl 2-deoxy- D -erythro-pentofuranosyl chloride ( 28 ) afforded an α, β mixture of 2-deoxy nucleosides. The synthesis of certain 3-substituted pyridazine 2′-deoxy necleosides are reported.     

Aldehyde Intermediates in the Synthesis of Tacamine-Type Indole Alkaloids: Preparation of (±)-apotacamine

The synthesis of aldehyde intermediates suitable for the preparation of indole alkaloids of the tacamine ( 1 ) type is described. The four possible aldehydes 4–7 were prepared from methyl 5-ethylnicotinate ( 8 ) in a few simple steps using a base-catalyzed epimerization as the final step (Schemes 1 and 2). The key aldehyde 4 , which is an analogue of the important vincamine intermediate 3 (‘Oppolzer's aldehyde’), was finally converted into the indole alkaloid (±)-apotacamine ( 21 ).     

Probing ruthenium-acetylide bonding interactions: synthesis, electrochemistry, and spectroscopic studies of acetylide-ruthenium complexes supported by tetradentate macrocyclic amine and diphosphine ligands

The synthesis and spectroscopic properties of trans-[RuL4(C[triple bond]CAr)2] (L4 = two 1,2-bis(dimethylphosphino)ethane, (dmpe)2; 1,5,9,13-tetramethyl-1,5,9,13-tetraazacyclohexadecane, 16-TMC; 1,12-dimethyl-3,4:9,10-dibenzo-1,12-diaza-5,8-dioxacyclopentadecane, N2O2) are described. Investigations into the effects of varying the [RuL4] core, acetylide ligands, and acetylide chain length for the [(-)C[triple bond]C(C6H4C[triple bond]C)(n-1)Ph] and [(-)C[triple bond]C(C6H4)(n-1)Ph] (n = 1-3) series upon the electronic and electrochemical characteristics of trans-[RuL4(C[triple bond]CAr)2](0/+) are presented. DFT and TD-DFT calculations have been performed on trans-[Ru(L')4(C[triple bond]CAr)2](0/+) (L' = PH3 and NH3) to examine the metal-acetylide pi-interaction and the nature of the associated electronic transition(s). It was observed that (1) the relationship between the transition energy and 1/n for trans-[Ru(dmpe)2{C[triple bond]C(C6H4C[triple bond]C)(n-1)Ph}2] (n = 1-3) is linear, and (2) the sum of the d(pi)(Ru(II)) --> pi*(C[triple bond]CAr) MLCT energy for trans-[Ru(16-TMC or N2O2)(C[triple bond]CAr)2] and the pi(C[triple bond]CAr) --> d(pi)(Ru(III)) LMCT energy for trans-[Ru(16-TMC or N2O2)(C[triple bond]CAr)2]+ corresponds to the intraligand pi pi* absorption energy for trans-[Ru(16-TMC or N2O2)(C[triple bond]CAr)2]. The crystal structure of trans-[Ru(dmpe)2{C[triple bond]C(C6H4C[triple bond]C)2Ph}2] shows that the two edges of the molecule are separated by 41.7 A. The electrochemical and spectroscopic properties of these complexes can be systematically tuned by modifying L4 and Ar to give E(1/2) values for oxidation of trans-[RuL4(C[triple bond]CAr)2] that span over 870 mV and lambda(max) values of trans-[RuL4(C[triple bond]CAr)2] that range from 19,230 to 31,750 cm(-1). The overall experimental findings suggest that the pi-back-bonding interaction in trans-[RuL4(C[triple bond]CAr)2] is weak and the [RuL4] moiety in these molecules may be considered to be playing a "dopant" role in a linear rigid pi-conjugated rod.     

Synthesis of [18,19,21,22‐13C4]‐Labeled Tautomycin as an NMR Probe of Protein Phosphatase Inhibitor

We have accomplished the synthesis of ¹³C‐labeled tautomycin at the C18, C19, C21, and C22 positions starting from 100 % [¹³C]triethylphosphonoacetate for the purpose of elucidating the dynamics and conformation of the C17–C26 moiety. NMR spectroscopy of ¹³C‐labeled tautomycin revealed strong binding with protein phosphatase type 1 and new features in the ¹³C NMR spectrum, such as the very small three‐bond coupling constants (²J).     

Utility of 4,6-dichloro-2-(methylthio)-5-nitropyrimidine. Part 2: Solution phase synthesis of tetrasubstituted purines

A simple synthesis of tetrasubstituted purines is disclosed based on the solution phase elaboration of 4,6-dichloro-2-methylthio-5-nitropyrimidine. One-pot sequential C4 and C6 chloride substitution by secondary and primary amines yields 4,6-diamino-2-methylthio-5-nitropyrimidines. mCPBA-mediated oxidation of the methylthio moiety to the corresponding sulfone allows facile substitution at the 2-position. CrCl₂ assisted reduction of the nitro group, followed by acid catalyzed orthoester cyclization, then provides novel tetrasubstituted purines not accessible by other methods.     

A Layer‐by‐Layer Film of Chitosan in a Taste Sensor Application

Chitosan is alternated with sulfonated polystyrene (PSS) to build layer‐by‐layer (LBL) films that are used as sensing units in an electronic tongue. Using impedance spectroscopy as the principle method of detection, an array using chitosan/PSS LBL film and a bare gold electrode as the sensing units was capable of distinguishing the basic tastes – salty, sweet, bitter, and sour – to a concentration below the human threshold. The suitability of chitosan as a sensing material was confirmed by using this sensor to distinguish red wines according to their vintage, vineyard, and brands.

PCA Plot for red wine samples obtained from impedance measurements at 1 kHz for the sensor array comprising a 3‐bilayer chitosan/PSS film and a bare gold electrode.     

PHOTOSENSITIZATION OF MURINE TUMOR, VASCULATURE and SKIN BY 5-AMINOLEVULINIC ACID-INDUCED PORPHYRIN

Abstract— The effects of topical and systemic administration of 5-aminolevulinic acid (ALA) were examined in several murine tumor systems with regard to porphyrin accumulation kinetics in tumor, skin and blood, vascular and tumor cell photosensitization and tumor response after light exposure. Marked, transient increases in porphyrin levels were observed in tumor and skin after systemic and topical ALA. Rapid, transient, dose-dependent porphyrin increases were also observed in blood; these were pronounced after systemic ALA injection and mild after topical application. They were highest within 1 h after ALA injection, thereafter declining rapidly. This matched the clearing kinetics of injected exogenous protoporphyrin IX (PpIX). Initially, vascular photosensitivity changed inversely to blood porphyrin levels, increasing gradually up to 5 h post-ALA, as porphyrin was clearing from the bloodstream. This pattern was again matched by injected, exogenous PpIX. After therapeutic tumor treatment vascular disruption of the tumor bed, while observed, was incomplete, especially at the tumor base. Minimal direct tumor cell kill was found at low photodynamic therapy (PDT) doses (250 mg/kg ALA, 135 J/cm² light). Significant, but limited (<1 log) direct photodynamic tumor cell kill was obtained when the PDT dose was raised to 500 mg/kg systemic ALA, followed 3 h later by 270 J/cm², a dose that was however toxic to the animals. The further reduction of clonogenic tumor cells over 24 h following treatment was moderate and probably limited by the incomplete disruption of the vasculature. Tumor responses were highest when light treatment was carried out at the time of highest tumor porphyrin content rather than at the time of highest vascular photosensitivity. Tumor destruction did not reach the tumor base, regardless of treatment conditions.     

Die Ringinversions-Barriere in [2.2]Metacyclophan

From racemization studies on optically active [2.2]metacyclophanes substituted in position 4, the parameters of activation for the inversion of the tenmembered ring were found to be: G ₄₂₃ =31.5 kcal/mole, H =27.5 kcal/mole and S =–10 Cl/mole.Racemization does not occurvia bond forming or breaking; the value for the inversion barrier is not affected by substituents in position 4 and therefore corresponds to the value of unsubstituted [2.2]metacyclophane, whereas substituents in the bridge exert a distinct influence. These results can easily be explained on the basis of the isoconformational concept.

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Herrn Prof. Dr.O. Hoffmann-Ostenhof mit besten Wünschen zum 60. Geburtstag gewidmet.     

Strukturviskosität von verdünnten Lösungen von Biopolymeren

The importance of the rheological behaviour of solutions of macromolecules is briefly evaluated. The viscosity of the solutions depends on concentration, shear rate and time of shear, this relation being determined by the structure of the dissolved molecules. In dilute solutions shear dependence of viscosity is very frequently caused by the preferential orientation of anisotropic molecules. In such a case the particle dimensions can be calculated from the true limiting viscosity number, an anisotropy factor, the rotational diffusion constant and the effective particle density. These numbers can be derived from the flow curve, which has been extrapolated to zero concentration. It is necessary to measure the flow curve at shear gradients, which are sufficiently low to allow for an extrapolation to vanishing shear rate. By comparing the experimental flow curve with a choice of theoretical ones, the rotational diffusion constant and the anisotropy factor (axial ratio) can be found. From the limiting viscosity number and the axial ratio, the particle density can be calculated.     

Special Mixing Behavior of Chelate-based Ionic Liquid with Methanol

Compared to the general ionic liquids (ILs), a significant deviation of the binary mixtures of 1-decyl-3-methylimidazolium tri(hexafluoroacetylaceto)-copper(II) ([C₁₀mim][Cu(hfacac)₃]) with methanol was found, indicating the way methanol interacts with ILs might be governed by the special structure of the chelating anion. IR results showed that the (C2-H) of 1-decyl-3-methylimidazolium hexafluoroacetylacetonate ([C₁₀mim][hfacac]) blue-shifted more significantly than that of [C₁₀mim][Cu(hfacac)₃], meanwhile the (C=O) red-shifted in [C₁₀mim][Cu(hfacac)₃], which is contrast with that in [C₁₀mim][hfacac]. Two-dimensional correlation analysis of the FTIR spectra indicated that the chelating cavity has little effect on the sequence of the ILs sites that interact with methanol. Combined with small angle X-ray scattering (SAXS) results, the picture of mixing processes in these two systems were proposed. Methanol interacts directly with the anion followed by the cation in [C₁₀mim][hfacac], while methanol preferentially enters the chelating cavity and enhances the packing effect in the [C₁₀mim][Cu(hfacac)₃] system.