Cyclopolycondensations. VII. Preparation of aromatic poly(ureido acids) by the low-temperature solution polymerization and cyclodehydration to fully aromatic polyquinazolinediones

Fully aromatic polyquinazolinediones (IV) of high molecular weight were obtained by thermal cyclodehydration of aromatic poly(uredio acids) (III) prepared by the polyaddition reaction of 4,4′-diaminobiphenyl-3,3′-dicarboxylic acid (I) with aromatic diisocyanates (II). From the kinetic study of reactions of model systems (anthranilic acid with phenyl isocyanate) in the presence of a variety of basic catalysts, it was established that tertiary amines had the highest catalytic activity for the formation of ureido linkage. The optimum polymerization conditions were determined by the study of reaction variables such as monomer concentration, polymerization temperature, monomer ratio, and catalyst concentration. The effect of polarity and purity of organic solvents and reactants was also studied.     

Silica sol-gel/organic hybrid material for protein encapsulated column of capillary electrochromatography

A new-type of sol-gel/organic hybrid composite material using gelatin or chitosan with tetramethoxysilane was developed for the bovine serum albumin (BSA)-encapsulated monolithic column for capillary electrochromatography (CEC). The composite monolith was used to immobilize BSA in a fused-silica capillary. The addition of gelatin and chitosan to the alkoxysilane enabled the enantioseparation of Trp. A very small amount of these polymers were effective for the enantioseparation. Especially, the monolithic column prepared from chitosan with tetramethoxysilane showed a high enantioselectivity for Trp enantiomers and the value (alpha' = t2/t1, t1: fast eluted enantiomer, t2: second eluted enantiomer) reached 1.15 on CEC mode. Furthermore, the composite materials exhibited a higher stability compared to the silica sol-gel column. These results showed that the sol-gel/organic hybrid composite was useful as a monolithic matrix for the BSA-encapsulated column for CEC.     

Reaction of 2-methoxy-3H-azepine with NBS: efficient synthesis of 2-substituted 2H-azepines

[reaction: see text] The reaction of 2-methoxy-3H-azepines, in the presence or absence of a nucleophile, with N-bromosuccinimide (NBS) gave a regioselective 1,4-adduct from which the corresponding 2H-azepine derivatives were formed via base-promoted hydrogen bromide elimination, generally in moderate to quantitative yield. Competitive formation of 4-bromo-2-methoxy-3H-azepine by electrophilic substitutuion or 3H-azepin-2-yl 2H-azepin-2-yl ether by transetherification was minimized at lower reaction temperatures. Quantitative substitution of 2-(2',4',6'-trichlorophenoxy)-2H-azepine derivatives, formed in moderate yield from the respective 3H-azepine and NBS in the presence of 2,4,6-trichlorophenol (TCP), by various nucleophiles gave the corresponding 2-substituted 2H-azepine. Among these nucleophiles were alkanethiol and alkylamine that are not tolerated in the reaction of 3H-azepine and NBS.     

Hydrogen atom abstraction by methyl radicals in methanol glasses at 15–100 K: evidence for a limiting rate constant below 40 K by quantum-mechanical tunneling

Rate constants for hydrogen atom abstraction by methyl radicals in methanol glasses have been measured from 100 to 15 K. The Arrhenius plot is nonlinear and the reaction rate constant appears to reach a limiting value below 40 K. The results are discussed in terms of simple models for quantum-mechanical tunneling in the solid state at low temperatures. Assuming that the methyl group rotation in methanol brings about a merging of the energy level distribution at the potential barrier, the observation of temperature-independent rate constants below 40 K may be attributable to a freezing out of this rotation such that tunneling occurs only from the zero-point vibrational level.     

Mechanisms and kinetics of noncatalytic ether reaction in supercritical water. 2. Proton-transferred fragmentation of dimethyl ether to formaldehyde in competition with hydrolysis

Noncatalytic reaction pathways and rates of dimethyl ether (DME) in supercritical water are determined in a tube reactor made of quartz according to liquid- and gas-phase 1H and 13C NMR observations. The reaction is studied at two concentrations (0.1 and 0.5 M) in supercritical water at 400 degrees C and over a water-density range of 0.1-0.6 g/cm3. The supercritical water reaction is compared with the neat one (in the absence of solvent) at 0.1 M and 400 degrees C. DME is found to decompose through (i) the proton-transferred fragmentation to methane and formaldehyde and (ii) the hydrolysis to methanol. Formaldehyde from reaction (i) is consecutively subjected to four types of redox reactions. Two of them proceed even without solvent: (iii) the unimolecular proton-transferred decarbonylation forming hydrogen and carbon monoxide and (iv) the bimolecular self-disproportionation generating methanol and carbon monoxide. When the solvent water is present, two additional paths are open: (v) the bimolecular self-disproportionation of formaldehyde with reactant water, producing methanol and formic acid, and (vi) the bimolecular cross-disproportionation between formaldehyde and formic acid, yielding methanol and carbonic acid. Methanol is produced through the three types of disproportionations (iv)-(vi) as well as the hydrolysis (ii). The presence of solvent water decelerates the proton-transferred fragmentation of DME; the rate constant is reduced by 40% at 0.5 g/cm3. This is caused by the suppression of low-frequency concerted motion corresponding to the reaction coordinate for the simultaneous C-O bond scission and proton transfer from one methyl carbon to the other. In contrast to the proton-transferred fragmentation, the hydrolysis of DME is markedly accelerated by increasing the water density. The latter becomes more important than the former in supercritical water at densities greater than 0.5 g/cm3.     

A study on the conformation-anomeric effect-stereoselectivity relationship in anomeric radical reactions,using conformationally restricted glucose derivatives as substrates

We previously theorized that, since the stereoselectivity of anomeric radical reactions is significantly influenced by the kinetic anomeric effect, which can be controlled by restricting the conformation of the radical intermediate, the proper conformational restriction of the pyranose ring of the substrates would therefore make highly alpha- and beta-stereoselective anomeric radical reactions possible. This theory was based on our previous results of the anomeric radical reactions with d-xylose derivatives as the substrates. We herein report the anomeric radical deuteration reactions with the conformationally restricted 1-phenylseleno-d-glucose derivatives, 2g and 3g, restricted in a (4)C(1)-conformation by an O-cyclic diketal moiety, and 4g, 5g, 6g, 7g, and 8g, restricted in a (1)C(4)-conformation by bulky O-silyl protecting groups. The radical deuterations with Bu(3)SnD, using the (4)C(1)-restricted substrates 2g and 3g, afforded the corresponding alpha-products (alpha/beta = 98:2) highly stereoselectively, whereas the (1)C(4)-restricted substrate 6g, having a trigonal (sp(2)) carbon substituent, i.e., -CHO, at the 5-position, selectively gave the beta-products (alpha/beta = 0:100). Thus, the stereoselectivity was significantly increased by the conformational restriction and was completely inverted by changing the substrate conformation from the (4)C(1)-form to the (1)C(4)-form. On the other hand, the deuterations with the (1)C(4)-restricted substrates 4g and 5g showed that the 1,5-steric effect due to the tetrahedral carbon substituent (-CH(2)OTIPS or -CH(2)OH) at the 5-axial position dominantly prevented the hydride transfer from the beta-face competing with the kinetic anomeric effect. This study suggests that, depending on the restricted conformation of the substrates to the (4)C(1)- or the (1)C(4)-form, the alpha- or beta-products would be obtained highly stereoselectively via anomeric radical reactions of hexopyranoses.     

Synthesis of TiRru2 heterobimetallic and TiRuM (M = Rh, Rr, Pd, Pt) heterotrimetallic sulfido clusters from a hydrosulfido-bridged titanium-ruthenium complex

Treatment of the hydrosulfido-bridged titanium-ruthenium heterobimetallic complex [Cp2Ti(mu2-SH)2RuCl(eta5-C5Me5)] (1; Cp = eta5-C5H5) with an excess of triethylamine followed by addition of [RuCl2(PPh3)3] and [[(cod)M]2(mu2-Cl)2] (M = Rh, Ir; cod = 1,5-cyclooctadiene) led to the formation of the TiRu2 and TiRuM mixed-metal sulfido clusters [(CpTi)[(eta5-C5Me5)Ru][Ru(PPh3)2](mu3-S)2(mu2-Cl)2] (3) and [(CpTi)[(eta5-C5Me5)Ru][M(cod)](mu3-S)2(mu2-Cl)] (M = Rh (4a), Ir (4b)), respectively. On the other hand, the reactions of 1 with [M(PPh3)4] (M = Pd, Pt) afforded the TiRuM trinuclear clusters [(CpTiCl)[(eta5-C5Me5)Ru][M(PPh3)2](mu3-S)(mu2-S)(mu2-H)] (M = Pd (5a), Pt (5b)) with an unprecedented M3(mu3-S)(mu2-S) core. The detailed structures of these triangular clusters 3-5 have been determined by X-ray crystallography. Crystal data: 3, triclinic, P1, a = 12.448(4) A, b = 12.773(4) A, c = 17.270(4) A, alpha = 100.16(2) degrees, beta = 99.93(2) degrees, gamma = 114.11(3) degrees, V = 2373(1) A(3), Z = 2; 4a, triclinic, P1, a = 7.714(2) A, b = 11.598(3) A, c = 14.802(4) A, alpha = 80.46(2) degrees, beta = 82.53(2) degrees, gamma = 71.47(2) degrees, V = 1234.0(6) A3, Z = 2; 4b, triclinic, P1, a = 7.729(1) A, b = 11.577(2) A, c = 14.766(3) A, alpha = 80.14(1) degrees, beta = 82.71(1) degrees, gamma = 71.55(1) degrees, V = 1231.1(4) A3, Z = 2; 5a, monoclinic, P2(1)/c, a = 11.259(4) A, b = 16.438(4) A, c = 26.092(5) A, beta = 102.23(3) degrees, V = 4719(2) A(3), Z = 4; 5b, monoclinic, P2(1)/n, a = 11.369(2) A, b = 16.207(3) A, c = 26.116(2) A, beta = 102.29(1) degrees, V = 4701(1) A3, Z = 4.     

Specific adenine alkylation by pyrrole-imidazole CBI conjugates

We examined DNA alkylation by pyrrole (Py)-imidazole (Im) hairpin polyamides, which possess 1,2,9,9a-tetrahydrocyclopropa[1,2-c]benz[1,2-e]indol-4-one (CBI) or cyclopropapyrroloindole (CPI) as DNA alkylating moieties. High-resolution denaturing gel electrophoresis revealed that alkylation by CBI conjugates 2 and 4 occurred specifically at adenines (A) in matched sequences, whereas CPI conjugates 1 and 3 alkylated both A and guanines (G) in matched sequences. The origin of the different reactivity of CBI and CPI conjugates is discussed in relation to the electrophilicity of the cyclopropane moiety. The high selectivity of the CBI conjugate gives additional sequence specificity relative to CPI conjugates that would be useful for the biological applications.     

Novel A-seco-rearranged lanostane triterpenoids from Abies sachalinensis

From the needles of Abies sachalinensis, novel rearranged lanostane type triterpenes, 1-4, were isolated along with a known triterpene (5). The structures of the new compounds, 1-4, were elucidated to be 3,4-seco-8-(14-->13R)abeo-17,13-friedo-9beta-lanosta-4(28),7,14(30),22Z,24-pentaen-26,23-olide-3-oic acid, methyl 3,4-seco-8-(14-->13R)abeo-17,13-friedo-9beta-lanosta-4(28),7,14(30),22Z,24-penten-26,23-olide-3-oate, 3,4-seco-8(14-->13R)abeo-17,13-friedo-9beta-lanosta-4(28),7,14,22Z,24-pentaene-26,23-olide-3-oic acid and methyl 3,4-seco-8(14-->13R)abeo-17,13-friedo-9beta-lanosta-4(28),7,14,22Z,24-pentaene-26,23-olide-3-oate, respectively, by means of spectral experiments, especially two dimensional NMR spectroscopy, such as 1H-detected multiple quantum coherence (HMQC), 1H-detected heteronuclear multiple bond connectivity (HMBC) and 1H-1H-correlation spectroscopy (COSY) experiments. These new compounds have novel structures containing A-seco, rearranged spiro structure and a gamma-lactone conjugated with a diene. Some of these compounds showed potent antibacterial activity against gram positive bacteria.     

GalnAsP-InP double-heterostructure lasers

GaInAsP-InP double-heterostructure lasers which are the most promising optical sources for the long wavelength region have been investigated. In the crystal growth, it was found that the liquidus and solidus isotherms are affected by the orientation of InP source and substrate crystals in the liquid phase epitaxial growth of GaInAsP alloys. The unit cell of the GaInAsP epitaxial layer is tetragonally deformed due to the interface lattice misfit such that the lattice constant parallel to the wafer surface is invariant across the interfaces in the GaInAsP-InP wafers. Two kinds of stripe lasers, planar stripe and buried lasers, have been fabricated by use of GaInAsP cap layer for good p-type contact. The planar stripe lasers of 10,15 and 20 m wide stripe operated in fundamental-transverse mode with 20–30% differential external efficiencies per facet. The 15 m wide stripe laser showed good mode characteristics to operate in a fundamental-transverse mode up to the cw output power of 22 mW per facet and in a single longitudinal mode over a wide range of currents. The buried stripe laser operated in a fundamental-transverse mode with the threshold current as low as 30 mA by making the stripe width narrower than 2 (m. The laser succeeded in cw operation at 100 °C because of its low threshold current and low thermal resistance.The authors would like to thank K. Noda, N. Kuroyanagi and Y. Furukawa for their encouragement. Thanks are also due to H. Kano for permission to use his results of buried stripe lasers prior to publication, and S. Ando for his technical assistance.