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771.
Diffusion is a spontaneous process and one of the physicochemical phenomena responsible for molecular transport, the rate of which is governed mainly by the diffusion coefficient; however, few coefficients are available because the measurement of diffusion rates is not straightforward. The translational diffusion coefficient is related by the Stokes–Einstein equation to the approximate radius of the diffusing molecule. Therefore, the stable conformations of small molecules were first calculated by molecular modeling. A simple radius rs and an effective radius re were then proposed and estimated using the stable conformers with the van der Waals radii of atoms. The diffusion coefficients were finally calculated with the Stokes–Einstein equation. The results showed that, for the molecules with strong hydration ability, the diffusion coefficients are best given by re and for other compounds, rs provided the best coefficients, with a reasonably small deviation of ~0.3 × 10−6 cm2/s from the experimental data. This demonstrates the effectiveness of the theoretical estimation approach, suggesting that diffusion coefficients have potential use as an additional molecular property in drug screening. 相似文献
772.
Dr. Junpei Matsuoka Dr. Shinsuke Inuki Yuka Matsuda Dr. Yoichi Miyamoto Mayumi Otani Prof. Dr. Masahiro Oka Prof. Dr. Shinya Oishi Prof. Dr. Hiroaki Ohno 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(49):11150-11157
The total synthesis of dictyodendrins A–F was achieved by using the gold(I)-catalyzed annulation of a conjugated diyne with N-Boc-pyrrole for direct construction of the pyrrolo[2,3-c]carbazole scaffold. Late-stage functionalization of the resulting pyrrolo[2,3-c]carbazole to introduce various substituents provided divergent access to dictyodendrins. Some dictyodendrin analogues exhibited inhibitory activities toward CDK2/CycA2 and GSK3. 相似文献
773.
Dr. Jungkweon Choi Sachiko Tojo Dr. Doo-Sik Ahn Prof. Dr. Mamoru Fujitsuka Shunichi Miyamoto Prof. Dr. Kazuo Kobayashi Prof. Dr. Hyotcherl Ihee Prof. Dr. Tetsuro Majima 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(32):7711-7718
Despite numerous experimental and theoretical studies, the proton transfer accompanying the oxidation of 2′-deoxyadenosine 5′-monophosphate 2’-deoxyadenosine 5’-monophosphate (5’-dAMP, A ) is still under debate. To address this issue, we have investigated the oxidation of A in acidic and neutral solutions by using transient absorption (TA) and time-resolved resonance Raman (TR3) spectroscopic methods in combination with pulse radiolysis. The steady-state Raman signal of A was significantly affected by the solution pH, but not by the concentration of adenosine (2–50 mm ). More specifically, the A in acidic and neutral solutions exists in its protonated ( A H+(N1+H+)) and neutral ( A ) forms, respectively. On the one hand, the TA spectral changes observed at neutral pH revealed that the radical cation ( A .+) generated by pulse radiolysis is rapidly converted into A .(N6−H) through the loss of an imino proton from N6. In contrast, at acidic pH (<4), A H.2+(N1+H+) generated by pulse radiolysis of A H+(N1+H+) does not undergo the deprotonation process owing to the pKa value of A H.2+(N1+H+), which is higher than the solution pH. Furthermore, the results presented in this study have demonstrated that A , A H+(N1+H+), and their radical species exist as monomers in the concentration range of 2–50 mm . Compared with the Raman bands of A H+(N1+H+), the TR3 bands of A H.2+(N1+H+) are significantly down-shifted, indicating a decrease in the bond order of the pyrimidine and imidazole rings due to the resonance structure of A H.2+(N1+H+). Meanwhile, A .(N6−H) does not show a Raman band corresponding to the pyrimidine+NH2 scissoring vibration due to diprotonation at the N6 position. These results support the final products generated by the oxidation of adenosine in acidic and neutral solutions being A H.2+(N1+H+) and A .(N6−H), respectively. 相似文献
774.
Mitsuji Yamashita Akihito Iida Hiroyuki Mizuno Yasushi Miyamoto Toru Morishita Naoaki Sata Kenji Kiguchi Akihiro Yabui Tatsuo Oshikawa 《Heteroatom Chemistry》1993,4(6):553-557
Reactions of 1-phenyl- and 1-methoxy-2-phospholene 1-oxides with bromine in aqueous organic solvents or in a protic medium, such as methanol, easily afforded the corresponding 2-bromo-3-hydroxy- or 2-bromo-3-methoxyphospholane 1-oxide derivatives. The reaction mechanism was postulated based on the stereochemistry of the products. 相似文献
775.
776.
Haruyuki Okamura Masahiko Minoda Takeshi Fukuda Takeaki Miyamoto Koichi Komatsu 《Macromolecular rapid communications》1999,20(2):37-40
Four samples of C60‐(PS)2, i. e., C60 fullerenes with two low‐polydispersity PS arms at the 1,4‐positions, were studied with respect to their solubility and dispersion state in a PS (polystyrene) matrix by the UV spectroscopic method. C60‐bearing polymers were found to be dispersed, in a blend film or a bulk film of itself, either monomolecularly or in aggregates, depending on the chain length of the polymer moiety and blend composition. 相似文献
777.
Construction of α-phosphonolactams via rhodium (II)-catalyzed intramolecular C?H insertion reactions
Yoshiharu Okada Toru Minami Masahiro Miyamoto Tsuneyuki Otaguro Sumiko Sawasaki Junji Ichikawa 《Heteroatom Chemistry》1995,6(3):195-210
The Rh(II)-catalyzed intramolecular C H insertion reactions of N,N-dialkyl-α-diazo-α-(diethylphosphono)acetamides 2a , f–j in CHCl3 or ClCH2CH2Cl were found to give monocyclic and bicyclic α-phosphono-β-lactams, 3a and 3f–j , in 43–67% yields via regiospecific α-C H insertion of the N-alkyl groups. Similar treatment of N-benzyl-N-isopropyl-α-diazo-α-(diethylphosphono)acetamide ( 2b ) and the corresponding N-isobutyl-N-methylacetamide 2d in ClCH2CH2Cl afforded mixtures of β-lactams 3b (35%) and and 3b ′ (16%), β-lactam 3d (47%), and γ-lactam 4d (10%), respectively, each of which is formed by the competitive C H insertion reaction between benzylic and isopropyl α-C H bonds and between methyl α-C H and methine β-C H bonds, respectively. For the formation of β-lactams, the selectivity in the rhodium-mediated C H insertion in ClCH2CH2Cl follows the order methyl > methine > benzylic α-C H bond on N-substituents. The N,N-dibutyl-α-diazo homologue 2c and Nα[α-diazo-α-(diethylphosphono)acetyl]-2-methylindoline ( 2k ) exclusively produced γ-lactams 4c (67%) and 4k (81%) via insertion into the methylene β-C H and methyl β-C H bonds. tert-Butyl N-[α-diazo-α-(dibenzylphosphono)acetyl]-piperidine-2-carboxylate ( 2m ) on similar treatment, followed by deprotection of the benzyl ester afforded the 7-phosphono carbacepham 6 in 32% overall yield. Similar Rh(II)-catalyzed cyclization of N-methyl-N[4-benzyloxy-α-(diethylphosphono)-phenyl(diethyl-phosphono)methyl]-α-diazo-acetamide ( 2n ) led to 1-[4′-benzylphenyl(diethylphosphono)methyl] -3-(diethyl-phosphono)azetidin-2-one ( 3n ) in 78% yicld. The phosphono group at C-7 of 3f was converted into the acetylamino group via a four-step reaction. Application of chiral rhodium(II) carboxylates 12a–c to the insertion reactions of 2b , c produced α-phosphono-β-and γ-lactams, 3b and 4c , in 6–24% ee and 25–29% ee, respectively. 相似文献
778.
Takeo Saegusa Keigo Aoi Masatoshi Miyamoto Yoshiki Chujo 《Macromolecular Symposia》1991,47(1):163-177
Characteristics of the polymerization mechanisms of the family of cyclic imino ethers are described. The variety of the mechanism of propagation has been systematized on the basis of the nature of propagating species, i.e., cationic or electrophilic covalent (dipole) species. In the polymerizations of 2-alkyl cyclic imino ethers (5- and 6-membered), propagation mechanism via one of these two different species has been established, which is dependent upon the relative nucleophilic reactivities of the monomer and the counter anion derived from initiator. The polymerization of cyclic pseudoureas having a cyclic amine substituent at 2-position proceeds in two different ways. Ionic propagation leads to the single isomerization/ring-opening polymerization involving only the cyclic imino ether ring. On the other hand, covalent propagation gives rise to the double isomerization ring-opening polymerization involving the two rings of cyclic imino ether and cyclic amine. Polymerization of 5-membered cyclic iminocarbonate with a sulfonate initiator proceeds through the isomerization/ring-opening of 2-oxazoline ring. The same monomer was isomerized to the corresponding cyclic urethane when it was treated with benzyl bromide. 相似文献