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21.
Hidetake Sakuraba Hiroshi Maekawa 《Journal of inclusion phenomena and macrocyclic chemistry》2006,54(1-2):41-45
The two modified β-cyclodextrin (β-CD) derivatives having catechol-type ligand (2,3- and 3,4-dihydroxy groups on the benzoate
ring) were synthesized. The chiral catalytic activity of their MoV and CuII complexes was examined in the asymmetric oxidation of aromatic sulfides using hydrogen peroxide in water (pH 6.0). The oxidation
with the MoV complexes of two β-CD derivatives were more accelerated than that with the CuII complexes. The sign of the optical rotation of the sulfoxides obtained in the above two cases showed the opposite configuration
in the oxidation of the same sulfide. The difference of the enantioselectivity appeared also between the two complexes of
the 2,3- and 3,4-dihydroxybenzoate derivatives with the same metal ion. While the use of the MoV complexes with the catechol derivatives yielded the sulfoxides with 35–65% ee, the use of the CuII complexes gave the products with the␣opposite configuration at 26–52% ee. The chiral induction in the oxidation, observed
conversely between the␣catalysts, was reflected on the chiral conformation of the respective metal catalysts, showed in Induced
Circular Dichroism (ICD) spectra. The highest optical yield, 65%, was observed in the oxidation of butyl phenyl sulfide using
the catalytic amount (0.1 equiv) of the MoV complex with mono-6-O-(3,4-dihydroxybenzoyl)-β-CD. The reaction gave predominantly the (S)-sulfoxide in 95% chemical yield. 相似文献
22.
Takagi R Miyanaga W Tamura Y Ohkata K 《Chemical communications (Cambridge, England)》2002,(18):2096-2097
The Diels-Alder reaction of spirolactones with cyclopentadiene afforded the adduct with high pi-facial selectivity; a hydrophilic analogue of scyphostatin was synthesized from the Diels-Alder adduct. 相似文献
23.
Maekawa K Shiomi D Ise T Sato K Takui T 《The journal of physical chemistry. B》2005,109(19):9299-9304
Spin alignments in heterospin chains are examined from numerical calculations of model spin Hamiltonians. The Hamiltonians of the heterospin chains mimic an open-shell molecular assemblage composed of an organic biradical in a singlet (S = 0) ground state and a doublet (S = 1/2) monoradical, which are coupled by intermolecular ferromagnetic exchange interactions. It is found from numerical calculations of the spin Hamiltonians that the spin value S2 of the ground-state singlet biradical embedded in the exchange-coupled assemblage deviates from zero and contributes to the bulk magnetization. The alternating chain is found to have two kinds of ground spin states, a high- and a low-spin state. All the spins are parallel to each other in the high-spin state, which is characterized by the spin correlation function of (S(i).S(j)) = 0.25. On the other hand, the spin alignment in the low-spin state is found to be dependent on the topology of the intermolecular exchange interactions. The energy preference of the two states depends on the relative amplitude of the exchange interactions in the chain. The intermolecular ferromagnetic couplings are competing in the ground-state singlet biradical with the intramolecular antiferromagnetic interaction. The appearance of the two kinds of ground states is attributed to a quantum spin frustration effect inherent in the triangular motif of the competing interactions. Magnetic properties of a zigzag chain complex composed of a nitronyl nitroxide biradical with a singlet ground state and Cu(hfac)2 are examined on the basis of the theoretical calculations. The vanishing magnetic moments, or the product of susceptibility and temperature chiT, at low temperatures observed for the complex are consistent with those of the low-spin state predicted in the theoretical calculations. 相似文献
24.
Zhenya Zhang Taisheng Quan Pomin Li Yansheng Zhang Norio Sugiura Takaaki Maekawa 《Applied biochemistry and biotechnology》2004,115(1-3):1033-1039
We studied biogas fermentation from alcohol waste fluid to evaluate the anaerobic digestion process and the production of
vitamin B12 as a byproduct. Anaerobic digestion using acclimated methanogens was performed using the continuously stirred tank reactor
(CSTR) and fixed-bed reactor packed with rock wool as carrier material at 55°C. We also studied the effects of metal ions
added to the culture broth on methane and vitamin B12 formation. Vitamin B12 production was 2.92 mg/L in the broth of the fixed-bed reactor, twice that of the CSTR. The optimum concentrations of trace
metal ions added to the culture liquid for methane and vitamin B12 production were 1.0 and 8 mL/L for the CSTR and fixed-bed reactor, respectively. Furthermore, an effective method for extracting
and purifying vitamin B12 from digested fluid was developed. 相似文献
25.
Yukiko Kato 《Tetrahedron letters》2006,47(15):2501-2505
We have developed the chemo- and regioselective phosphitylation of unprotected 2′-deoxyribonucleosides by the use of di-tert-butyl N,N-diethylphosphoramidite, a sterically hindered phosphoramidite. Both N/O- and primary hydroxy group-selectivities were simultaneously achieved, and the selectivity for the 5′-hydroxy groups was up to 97% regardless of the base moiety of the 2′-deoxyribonucleosides. The 3′-O-isomers and the 5′-O-isomers were easily separated by silica gel column chromatography or crystallization to give the pure 2′-deoxyribonucleoside 5′-phosphites in moderate to good yields. 相似文献
26.
27.
The α-haloester having an internal double bond was allowed to react with a catalytic amount of Pd(PPh3)4 to afford a cyclized product in a fairly good yield and the same product was obtained by treatment with Pd(OAc)2 to ketene silyl acetal. 相似文献
28.
Stereoblock poly(lactic acid) consisting of D- and L-lactate stereosequences can be successfully synthesized by solid-state polycondensation of a 1:1 mixture of poly(L-lactic acid) and poly(D-lactic acid). In the first step, melt-polycondensation of L- and D-lactic acids is conducted to synthesize poly(L-lactic acid) and poly(D-lactic acid) with a medium-molecular-weight, respectively. In the next step, these poly(L-lactic acid) and poly(D-lactic acid) are melt-blended in 1:1 ratio to allow formation of their stereocomplex. In the last step, this melt-blend is subjected to solid-state polycondensation at temperature where the dehydrative condensation is allowed to promote chain extension in the amorphous phase with the stereocomplex crystals preserved. Finally, stereoblock poly(lactic acid) having high-molecular-weight is obtained. The stereoblock poly(lactic acid) synthesized by this way shows a higher melting temperature in consequence of the controlled block lengths and the resulting higher-molecular-weight. The product characterization as well as the optimization of the polymerization conditions is described. Changes in M(w) of stereoblock poly(lactic acid) (sb-PLA) as a function of the reaction time. 相似文献
29.
Seiko Nan'ya Etur Maekawa Hitoshi Hayakawa Yukio Kitaguchi Yoshio Ueno 《Journal of heterocyclic chemistry》1985,22(6):1483-1485
The 5H-pyrido[2,3-a]phenoxazin-5-one derivatives and 5H-pyrido[3,2-a]phenoxazin-5-one derivatives were prepared by the condensation of substituted 2-aminophenols with 6,7-dibromo-5,8-quinolinequinone followed by dehalogenation in the presence of sodium hydrosulfite dissolved in aqueous pyridine under a nitrogen atmosphere. 相似文献
30.
Kei Maekawa 《Tetrahedron》2004,60(45):10293-10304
The irradiation of substituted (Z)-N-aroyl-α-dehydronaphthylalaninamides [(Z)-1] in methanol containing triethylamine (TEA) with Pyrex-filtered light was found to give 3,4-dihydrobenzoquinolinone derivatives (2) in high yields along with minor amounts of 4,5-dihydrooxazole derivatives (3). Analysis of the substituent effects on product composition revealed that both the photoreactivity of 1 and the selectivity of 2 are decreased with increasing electron-withdrawing ability of the substituent introduced at the para-position on the N-benzoyl benzene ring. From the analysis of the dependence of the quantum yield for the formation of 2 on the TEA concentration, it was found that back electron transfer occurs efficiently within an (E)-1 anion radical-TEA cation radical pair intermediate. 相似文献