Syntheses and spectral properties of 2,3,7,8-tetracyano-5,10-dihydrodipyrazino[2,3-b:2′,3′-e]pyrazine

Base catalized intermolecular cyclization of 2-amino-3-chloro-5,6-dicyanopyrazines gave 5,10-disubsti-tuted-2,3,7,8-tetracyano-5,10-dihydrodipyrazino[2,3-b:2′,3′-c]pyrazines 11–20. These compounds have rather small molecular size but have strong intramolecular charge-transfer chromophoric system. They have strong fluorescence in solution and some have fluorescence even in the solid state which are very important to evaluate their electroluminescence property as an emitter for electroluminescence devices. The physical, structural, and electronic properties of these new 2,3,7,8-tetracyano-5,10-dihy-drodipyrazino[2,3-b:2′3′-e]pyrazines were studied using uv-visible spectroscopy and the Pariser-Parr-Pople molecular orbital calculation method.     

N-substituted hydroxyureas as urease inhibitors

In order to seek a urease inhibitor more potent than hydroxyurea (1), its alkyl- or phenyl-substituted derivatives were synthesized and evaluated for their effect on the jack bean urease. Of 16 compounds tested, m-methyl- (10) and m-methoxy-phenyl substituted hydroxyurea (13) showed the most potent inhibitory activities against the enzyme.     

Product analyses of ozone mediated nitration of benzimidazole derivatives with nitrogen dioxide: formation of 1-nitrobenzimidazoles and conversion to benzotriazoles

Several benzimidazole derivatives having electron-withdrawing or -donating substituent(s) at the benzene moiety were used as models of the imidazole moiety of purine bases and their nitration with nitrogen dioxide and ozone (so-called Kyodai nitration) were examined. Products were extracted from the reaction mixture with AcOEt and their structures were analyzed. 1-Nitrobenzimidazole derivatives and unexpected 1-nitrobenzotriazole derivatives were identified. Although the yields of 1-nitrobenzimidazole derivatives were quite low, these were all new compounds that could be obtained only by Kyodai nitration. It was speculated that benzotriazoles were formed via 1-nitrobenzimidazoles and subsequent nitration toward benzotriazoles resulted in the formation of 1-nitrobenzotriazoles.     

Cyclopolycondensation. XII. Polymerization mechanism of polybenzoxazinones in polyphosphoric acid medium

The polymerization mechanism of polyphosphoric acid (PPA) solution polymerization of an aromatic diaminodicarboxylic acid with aromatic dicarboxylic acid derivatives was studied. By means of NMR methods, the initiation process for the polymerization of polybenzoxazinone in PPA medium was elucidated. The NMR spectra of a series of compounds were taken, and the salt formation of amino groups of monomer with PPA and the equilibrium between the salt and the free amino group were determined. It was established that the polymerization proceeded through the formation of phosphorylated intermediates to give the salt of amino groups of monomer with PPA. In the second step, the amine–PPA salt dissociates into the free amino group and PPA at the polymerization temperature above 140°C. Polymerization proceeds through the attack of “free” amino on phosphorylated carbonyl compounds to form polyamide acid of high molecular weight, and on subsequently being heated in PPA at higher temperatures, it undergoes an intramolecular cyclodehydration along the polymer chain to form polybenzoxazinones.     

Practical synthesis of [1-C]- and [6-C]-d-galactose

The chemical synthesis of ¹³C-labeled d-galactose as useful molecular probes for studying the conformation of oligosaccharides attached to proteins was performed. The method for synthesizing the title labeled compounds was newly developed via the corresponding 1-ene and 5-ene compounds derived from 1,2:5,6-di-O-isoproppylidene-α-d-galactofuranose by considering the efficient introduction of the atom. All protons of galactose from H-1 to H-6 were observed by the HMQC-HOHAHA technique using 1:1 mixtures of methyl [1-¹³C]- and [6-¹³C]-β-d-galactopyranoside, which were prepared from the title compounds.     

Conductance of nano-tube junctions and its scaling law

The conductance is calculated by Landauer’s formula with a simple tight binding model for junctions connecting two different metallic carbon nanotubes. These junctions are formed by a pair of disclinations, a 5-membered ring and a 7-membered ring, without dangling bonds. Conductances of about eight hundred kinds of junctions are obtained. The conductance is determined only by the ratio i/R where i is the distance between the two disclinations and R is the circumference of the thinner tube. When i/R ? 1, the conductance is found to be almost proportional to (i/R)^-3. Even when the Fermi energy is shifted by doping, an extended scaling law holds, so far as the channel number is kept two.     

Modification of pyridine-3-carboxamide (nicotinamide) by radical substitution

Pyridine-3-carboxamide ( 1 ) was reacted with alkyl radicals to give mono-, di-, and tri-alkylated products. The t-butyl radical gives only 6-t-butylpyridine-3-carboxamide ( 4a ). The reactivity decreases in the order of t-butyl, isopropyl, and ethyl radicals. The product 4a reacts further with the 2-phthalimidoethyl radical to give 2- and 4-substituted products 9 and 10 , which were transformed into tetrahydronaphthyridinone derivatives 11 and 12 .     

Cyclization of 5-amino-1-β-d-ribofuranosylimidazole-4-carboxamide (AICA-riboside): A review

The synthesis of various purine nucleosides by cyclization of AICA-riboside(5-amino-1-β-D-ribofuranosylimidazole-4-carboxamide) is described. A variety of cyclization reactions provide new synthetic routes to inosine and guanosine. In this review, emphasis will be placed on the synthesis of the latter.     

Introduction of functionalized C1, C2, and C3 units to imines through the dimethylzinc-air-initiated radical addition

Introduction of functionalized C1, C2, and C3 units to imines was achieved by using the dimethylzinc-air-initiated alpha-alkoxyalkyl radical addition as a key reaction. The addition to a C[double bond]N double bond chemoselectively occurred in the presence of a C[double bond]O double bond, which is one of the advantages of this radical addition reaction over ionic addition reactions.     

Reaction of 5-(3,4-dimethoxyphenyl)pyrazine-2,3-dicarbonitrile with alcohol in the presence of base

5-(3,4-Dimethoxyphenyl)pyrazine-2,3-dicarbonitrile reacts with methanol to give addition products, 3-methoxyiminopyrazine-2-carbonitrile and 2-methoxyiminopyrazine-3-carbonitrile derivatives, and/or substitution products, 3-methoxypyrazine-2-carbonitrile and 2-methoxypyrazine-3-carbonitrile derivatives. The selectivity between the addition and substitution depends on solvent polarity, base, and reaction time. The experimental results are accounted for by the equilibrium between the starting dinitrile and the addition products, methoxyiminopyrazine.