Intramolecularly hydrogen-bonded 3-phenacyl-lH-pyrido[3,4-b]-pyrazin-2-one and 2-Phenacyl-4H-pyrido[3,4-b]pyrazin-3-one

Twelve phenacyl derivatives of 1H-pyrido[3,4-b]pyrazin-2-ones and 4H-pyrido[3,4-b]pyrazin-3-ones have been synthesized. In these compounds, C = N double bonds at the 3 and 4 positions in the former compounds and those at the 1 and 2 positions in the latter compounds migrate onto the side chains to form phenacyli-dene structures. These migrations are facilitated by chelation between side chain carbonyl and the proton attached to the ring nitrogen atom which was generated by the migration. All the hydrogen-bonded structures appear to be stable as shown by their ir spectra in the crystalline state, and by their ¹H nmr spectra in solution.     

Structure of aszonalenin,a new metabolite of aspergillus zonatus

Aszonalenin ($\text{1}$) has been isolated from $\text{Aspergillus zonatus}$ together with LL-S490β ($\text{2}$) and the structure of $\text{1}$ has been established by spectroscopic evidences and chemical transformation.     

Specific heat and neutron diffraction study on quaternary sulfides BaNd2CoS5 and BaNd2ZnS5

Magnetic and electrical properties are investigated for quaternary neodymium sulfides BaNd₂TS₅ (T=Co, Zn) through the specific heat, neutron diffraction, and electrical conductivity measurements. Their electrical conductivities show semiconductive behavior, which follows the Arrhenius temperature dependence with the activation energy of E_a=1.46 eV for BaNd₂ZnS₅ and E_a=1.19 eV for BaNd₂CoS₅. The specific heat of BaNd₂ZnS₅ has a λ-type anomaly at 2.8 K due to the antiferromagnetic ordering of the Nd³⁺ moments and a Schottky-type anomaly at around 60 K, which results from the crystal field splitting of the ⁴I_9/2 ground state of the Nd³⁺ ion. The specific heat of BaNd₂CoS₅ shows two λ-type anomalies at 5.7 K due to the antiferromagnetic ordering of Nd³⁺ and at 58 K due to the antiferromagnetic ordering of Co²⁺. The latter overlaps with the Schottky-type anomaly due to the crystal field splitting of the Nd³⁺ ion. Neutron diffraction measurements for BaNd₂CoS₅ show that a magnetic arrangement of the Co²⁺ moments has a collinear antiferromagnetic structure, while that of the Nd³⁺ moments has a noncollinear one.     

Cationic ring-opening transfer polymerization of spiro ortho esters initiated by carbon black

The ring-opening transfer polymerization of spiro ortho esters (SOE) initiated by carbon black was investigated. In the absence of carbon black, no polymerization occurred at all. In the presence of channel black containing carboxyl group, the ring-opening transfer polymerization of SOE was initiated at 50-70°C. to give polyether ester, namely alternating copolymer of epoxide and lactone. The rate of polymerization of 1,4,6-trioxaspiro[4.4]nonane and 1,4,6-trioxaspiro[4.5]decane was considerably small compared with that of 1,4,6-trioxaspiro[4.6]undecane. The activation energy of the polymerization of 2-chloromethyl-1,4,6-trioxaspiro[4.6]undecane was estimated to be 6.0 kcal/mol. The initiating activity of carbon black increased with an increase in carboxyl group content of carbon black. Furnace black that contained no carboxyl group was unable to initiate the polymerization. Furthermore, the carbon black lost the initiating ability of the polymerization upon the blocking of carboxyl group on the surface by the treatment with potassium hydroxide or diazomethane. Based on these results, it was concluded that carboxyl group on carbon black plays an important role in the initiation. During the polymerization, a part of the polymer formed was grafted onto carbon black: the grafting ratio was 10–30%. The mechanisms of initiation and grafting were discussed.     

Uptake of alkali and alkaline earth metal ions into electrochemically pretreated glassy carbon fibres by flow-through electrolysis

When glassy carbon fibres are used, alkali and alkaline earth metal ions are adsorbed in the micropores which are created or activated by oxidative treatment of the fibres. The average pore radius was estimated to be 2 nm by nitrogen adsorption experiments. Uptake was studied with a flow system consisting of a flow-through carbon-fibre electrode; a dropping mercury electrode at the end of the flow line monitored changes in the metal ion concentrations. The ions were taken up at negative potentials and released at positive potentials. The amount taken up increased in the sequence Na⁺ < Li⁺ < H⁺, suggesting that the ions were desolvated before entering the pore system.     

Effect of TRX-liposomes size on their prolonged circulation in rats

Newly formulated cationic liposomes (TRX-liposomes) with four different mean diameters were injected into twelve male rats via the lateral tail vein in order to evaluate the effect of liposomal size on pharmacokinetic parameters. TRX-liposomes disappeared from the blood according to the one-compartment model and demonstrated maximum and minimum half-lives of ca. 14 h (mean diameter of 114.3 nm) and ca. 5 h (mean diameter of 285.9 nm), respectively. This prolonged half-life tended to decrease at the boundary of 114.3 nm mean diameter. The optimal size (114.3 nm) for prolonged circulation of TRX-liposomes was consistent with that of pegylated liposomes such as Doxil((R)), however, the half-life was different among these liposomes. The electric charge of the TRX-liposomal surface is assumed to be responsible for this difference. The results of the present study will be very useful in the design of long-circulating cationic liposomes.     

Finding of remarkable synergistic effect on the aroxyl-radical-scavenging rates under the coexistence of α-tocopherol and catechins

Measurements of aroxyl radical (ArO^•)-scavenging rate constants () of antioxidants (AOHs) (α-tocopherol (α-TocH) and three catechins (CatHs) (ie, epicatechin (EC), epigallocatechin (EGC), and epigallocatechin gallate (EGCG)) were performed in ethanol solution, using stopped-flow spectrophotometry. values were measured not only for each AOH, but also for the mixtures of two AOHs (α-TocH and CatH). A notable synergistic effect that the value of α-TocH increases 1.29, 1.84, and 1.65 times under the coexistence of constant concentrations of EC, EGC, and EGCG, respectively, was observed for the solutions including α-TocH and CatH. Similarly, values of CatHs (EC, EGC, and EGCG) increased 1.72, 2.25, and 2.34 times under the coexistence of constant concentrations of α-TocH, respectively. UV-Vis absorption of α-tocopheroxyl radical (α-Toc^•) (λ_max = 428 nm), which had been produced by reaction of α-TocH with ArO^•, decreased remarkably under the coexistence of α-TocH and CatHs due to the fast α-TocH-regeneration reaction by CatHs. The result suggests that the prooxidant reaction due to α-Toc^• is suppressed by the coexistence of CatHs. By analyzing the formation and decay curves of α-Toc^•, it has been ascertained that one molecule of EGCG having three OH groups at B-ring may rapidly regenerate three molecules of α-Toc^• to α-TocH.     

Cross-chiral examinations of molecular enantioselective recognition by fast atom bombardment mass spectrometry: Host–guest complexations between chiral crown ethers and chiral organic ammonium ions

Using fast atom bombardment (FAB) mass spectrometry (MS), cross-chiral relationships were confirmed for the first time for the diasteromeric host-guest complexations between the chiral crown ether host (1) and the chiral organic ammonium ion guest (2) on the basis of the relative peak intensities (RPI). Both host–guest combinations (R, R, R, R) – 1, (R) – 2 and (S, S, S, S) – 1, (S) – 2 obviously provided larger RPI values than the combination of both (R, R, R, R) – 1, (S) – 2 and (S, S, S, S) – 1, (R) – 2 by a factor of 1.6 as an averaged value: 1.87 (n = 4)/1.16 (n = 4) = 1.6. These results are consistent with the expected stabilities of the host-guest complexations by CPK model examinations. Successfully observed cross-chiral examinations strongly suggest a potentially useful FABMS/RPI methodology for rapidly searching newly designed and synthesized crown ether-like host compounds with a higher degree of enantioselectivity.     

Unambiguously confirmed structure of 2-phenacylidene-1,2-dihydro-4H-pyrido[2,3-b]pyrazin-3-one and 3-phenacylidene-3,4-dihydro-1H-pyrido[2,3-b]pyrazin-2-one

To determine the structures of two isomeric products, 2-phenacylidene-1,2-dihydro-4H-pyrido[2,3-b]pyrazin-3-one (2) and 3-phenacylidene-3,4-dihydro-1H-pyrido[2,3-b]pyrazin-2-one (3) obtained by condensation of 2,3-diaminopyridine (1) with ethyl benzoylpyruvate [1–3], these compounds were hydrolyzed to give 2-methyl-4H-pyrido[2,3-b]pyrazin-3-one (4) and 3-methyl-1H-pyrido[2,3-b]pyrazin-2-one (5) , respectively [4,5]. Both hydrolysates 4 and 5 were hydrogenated to afford 2-methyl-1,2-dihydro-4H-pyrido[2,3-b]pyrazin-3-one (6) and 3-methyl-3,4-dihydro-1H-pyrido[2,3-b]pyrazin-2-one (7) . The latter compound was identical with an unequivocally synthesized compound providing proof for the structures of all these compounds.     

Development of fast disintegrating compressed tablets using amino acid as disintegration accelerator: evaluation of wetting and disintegration of tablet on the basis of surface free energy

A fast disintegrating compressed tablet was formulated using amino acids, such as L-lysine HCl, L-alanine, glycine and L-tyrosine as disintegration accelerator. The tablets having the hardness of about 4 kgf were prepared and the effect of amino acids on the wetting time and disintegration time in the oral cavity of tablets was examined on the basis of surface free energy of amino acids. The wetting time of the tablets increased in the order of L-lysine HCl, L-alanine, glycine and L-tyrosine, whereas the disintegration time in the oral cavity of the tablets increased in the order of L-alanine, glycine, L-lysine HCl and L-tyrosine. These behaviors were well analyzed by the introduction of surface free energy. When the polar component of amino acid was large value or the dispersion component was small value, faster wetting of tablet was observed. When the dispersion component of amino acid was large value or the dispersion component was small value, faster disintegration of tablet was observed, expect of L-tyrosine tablet. The fast disintegration of tablets was explained by the theory presented by Matsumaru.