Regioselective synthesis of pyrido[2,3-d]pyrimidines

The reaction of diethyl ethoxymethylenemalonate ( 1 ) and 6-amino-1,3-dimethyluracil ( 2 ) was determined to be regioselective. Under acidic conditions the product was the previously isolated 7-oxopyrido[2,3-d]pyrimidine ( 3 ), while in the presence of one equivalent of base followed by thermal cyclization, the isomeric 5-oxopyrido[2,3-d]pyrimidine ( 5 ) is formed.     

Ermittlung kinetischer Parameter aus der Kurvenform für Reaktionen unter Aufheizung

Form indexes for DTA or TG curves (S _T orS _x) must be treated separately. Only forS _x can clear relations to be developed for the order of reactionn. In the rational range ofn between 0.5 and 3.0 we found for linear, exponential and hyperbolic programmes these functions were found to be of the type $$S_x = an^{0,5} + b$$ Since a low dependence on frequency factork ₀ has been established, for a linear programme the simultaneous determination ofn andk ₀ may be performed.     

Reactions of trivacant Wells-Dawson heteropolytungstates. Ionic strength and Jahn-Teller effects on formation in multi-iron complexes

Reaction of alpha-P(2)W(15)O(56)(12-) and Fe(III) in a saturated NaCl solution produces a trisubstituted Wells-Dawson structure with three low-valent metals, alpha-(Fe(III)Cl)(2)(Fe(III)OH(2))P(2)W(15)O(59)(11-) (1). Dissolution of this species into 1 M NaBr (Br(-) is non-coordinating) gives the triaquated species alpha-(Fe(III)OH(2))(3)P(2)W(15)O(59)(9-) (2). Ionic strength values of 1 M or greater are necessary to avoid decomposition of 1 or 2 to the conventional sandwich-type complex, alpha beta beta alpha-(Fe(III)OH(2))(2)Fe(III)(2)(P(2)W(15)O(56))(2)(12-) (3). If the pH is greater than 5, a new triferric sandwich, alpha alpha beta alpha-(NaOH(2))(Fe(III)OH(2))Fe(III)(2)(P(2)W(15)O(56))(2)(14-) (4), forms rather than 3. Like the previously reported Wells-Dawson-derived sandwich-type structures with three metals in the central unit ([TM(II)Fe(III)(2)(P(2)W(15)O(56))(P(2)TM(II)(2)W(13)O(52))],(16-) TM = Cu, Co), this complex has a central alpha-junction and a central beta-junction. Thermal studies suggest that 4 is more stable than 3 over a wide range of temperatures and pH values. The intrinsic Jahn-Teller distortion of d-electron-containing metal ions incorporated into the external sites of the central multi-metal unit impacts the stoichiometry of their incorporation (with a consequent change in the inter-POM-unit connectivity, where POM = polyoxometalate). Reaction of non-distorting Ni(II) with the diferric lacunary sandwich-type POM alpha alpha alpha alpha-(NaOH(2))(2)Fe(III)(2)(P(2)W(15)O(56))(2)(16-) (5) produces alpha beta beta alpha-(Ni(II)OH(2))(2)Fe(III)(2)(P(2)W(15)O(56))(2)(14-) (6), a Wells-Dawson sandwich-type structure with two Ni(II) and two Fe(III) in the central unit. All structures are characterized by (31)P NMR, IR, UV-vis, magnetic susceptibility, and X-ray crystallography. Complexes 4 and 6 are highly selective and effective catalysts for the H(2)O(2)-based epoxidation of alkenes.     

Thermally resistant polymers containing the s-triazine ring

Aromatic dinitriles cyclize to form aromatic polymers containing the s-triazine ring. In this paper, these polymers are compared thermally with each other and with aromatic melamine polymers prepared via the aromatic diamine and cyanuric chloride. One perfluoroaromatic melamine polymer was prepared and compared with the other two types of polymers. The polymers (triazines and melamine) in which biphenyl was the backbone were increasingly stable up to 1000°C. in nitrogen. The triazine polymers as a group were the most stable. The perfluoroaromatic polymer was the most stable melamine up to 500°C. in air but was very unstable above 700°C.     

A mass spectrometric analysis of CF4/O2 plasmas: Effect of oxygen concentration and plasma power

A quadrupole mass analyzer was used to detect the neutral products extracted downstream from a CF₄/O₂ RF discharge at 80 mtorr. mtorr. Stable discharge products were investigated as a junction of plasma power, residence time, oxygen concentration, and plasma voltage standing-wave ratio. In general, as plasma power increased from 10 to 200 W, production of CO increased while the measured mole fractions of CO₂ and COF₂ stabilized. The ratio of' CO to CO, decreases! at low plasma powers as the oxygen concentration increased. ,4n increase in the relative conversion of CF₄ to oxygenated products occurred at both low plasma powers and low oxygen concentrations. Chemical mechanisms are suggested to account for these results.     

Reactions of diphosphineplatinum(II) oxalate complexes with phenylacetylene. Formation of phenylalkynylplatinum complexes

[Pt(C₂O₄)(dppe)] reacts thermally with PhCCH to produce [Pt(CCPh)₂(dppe)], which has been prepared by alternative routes. Similar treatment of [Pt(C₂O₄)(dppm)] initially produces [Pt(CCPh)₂(dppm)], which rearranges to give cis,cis-[Pt₂(CCPh)₄(μ-dppm)₂]. Reaction of [PtCl₂(dppm)] with PhCCH/KOH/18-crown-6, or with (PhCC)SnMe₃, gives [Pt(CCPh)₂(dppm)], which may be converted to the cis,cis-dimer by addition of oxalic acid. Ultraviolet irradiation or refluxing with a trace amount of dppm converts [Pt(CCPh)₂(dppm)] to trans,trans-[Pt₂(CCPh)₄(μ-dppm)₂], but the cis,cis-dimer is stable under these conditions. [Pt(C₂O₄)L₂] (L = PPh₃, PEt₃) complexes also react thermally with PhCCH to yield [Pt(CCPh)₂L₂] species.     

Separation of lidocaine and its metabolites by capillary electrophoresis using volatile aqueous and nonaqueous electrolyte systems

The separation of the basic drug lidocaine and six of its metabolites has been investigated both by using volatile aqueous electrolyte system, at low pH and by employing non-aqueous electrolyte systems. In aqueous systems, the best separation of the compounds under the investigated conditions was achieved by using the electrolyte 60 mM trifluoroacetic acid (TFA)/triethylamine (TEA) at pH 2.5 containing 15% methanol. With this electrolyte, all seven compounds were well separated with high efficiency and migration time repeatability. The separations with bare fused-silica capillaries and polyacrylamide-coated capillaries were compared with higher separation efficiency with the latter. On the other hand, near baseline separation of all the seven compounds was also obtained by employing the non-aqueous electrolyte, 40 mM ammonium acetate in methanol and TFA (99:1, v/v), with comparable migration time repeatability but lower separation efficiency relative to the aqueous system.     

POTENTIATION OF MEROCYANINE 540-MEDIATED PHOTODYNAMIC THERAPY BY SALICYLATE and RELATED DRUGS

Abstract— Simultaneous exposure to merocyanine 540 (MC540) and light of a suitable wavelength kills leukemia, lymphoma and neuroblastoma cells but is relatively well tolerated by normal pluripotent hematopoietic stem cells. This differential phototoxic effect has been exploited in preclinical models and a phase I clinical trial for the extracorporeal purging of autologous bone marrow grafts. Salicylate is known to potentiate the MC540-mediated photokilling of tumor cells. Assuming that salicylate induces a change in the plasma membrane of tumor cells (but not normal hematopoietic stem cells) that enhances the binding of dye molecules it has been suggested that salicylate may provide a simple and effective means of improving the therapeutic index of MC540-mediated photodynamic therapy. We report here on a direct test of this hypothesis in a murine model of bone marrow transplantation as well as in clonal cultures of normal murine hematopoietic progenitor cells. In both systems, salicylate enhanced the MC540-sensitized photoinactivation of leukemia cells and normal bone marrow cells to a similar extent and thus failed to improve the therapeutic index of MC540 significantly. On the basis of a series of dye-binding studies, we offer an alternative explanation for the potentiating effect of salicylate. Rather than invoking a salicylate-induced change in the plasma membrane of tumor cells, we propose that salicylate displaces dye molecules from serum albumin, thereby enhancing the concentration of free (active) dye available for binding to tumor as well as normal hematopoietic stem cells.     

Preparation of animal tissue samples for the determination of90Sr and actinides

A unique procedure permitting the determination of⁹⁰Sr and actinides in the same protion of sample, with good chemical yields of all analytes, is presented. Animal tissue samples containing bone are ashed, spiked with^{2 3 2}U,^{2 4 2}Pu,^{2 4 3}Am and^{8 5}Sr and solubilized. The actinides and strontium are gathered and separated by a series of coprecipitations with, cerium hydroxide and cerium fluoride. Actinide separation and determination and purification and determination of⁹⁰Sr are accomplished by a combination of several well-known procedures. The laboratory method consistently results in high chemical yields of all the analytes and overcomes interferences from phosphates and calcium.