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991.
Simultaneous use of N-hydroxysuccinimide (HOSu) and CuCl2 with a HOSu-based uronium coupling reagent, O-(N-succinimidyl)-1,1,3,3-tetramethyluronium tetrafluoroborate, has been found to eliminate the racemization of the carboxy-terminal N-methylamino acid residue during the segment condensation. 相似文献
992.
Makoto Onaka Koji Ishikawa Yusuke Izumi 《Journal of inclusion phenomena and macrocyclic chemistry》1984,2(1-2):359-366
Alkali cation exchanged X- and Y-type zeolites are employed to promote the reactions of aniline derivatives with alkylating agents in organic solvent. The N-alkylation is accelerated by the cooperative function of the acid and base sites on the potassium cation exchanged X- and Y-type zeolites to give the N-monoalkylated product in very high selectivity. Especially the use of the zeolite is found to be effective for N-alkylation of deactivated aromatic amines like nitroaniline. The highly selective N-monoalkylation is attributed to the reaction occurring inside the homogeneous narrow cavities of zeolites. 相似文献
993.
K. Ishida T. Matsuzaki K. Nishiyama K. Nagamine Y. Miyake Y. Tabata Y. Ito 《Hyperfine Interactions》1984,19(1-4):933-937
The muon spin resonance method was applied to measure the
+ polarization corresponding to the muon state in diamagnetic compounds in CS2, water and benzene under 3 kG decoupling field. We observed almost the same diamagnetic polarizations under decoupling field, compared to those at zero decoupling field observed under the transverse field, except in CS2 The results indicate that most of the so called missing fraction is not associated with diamagnetic species produced as a final state of rapid chemical reactions of muonium in these samples.The authors acknowledge helpful discussions with Professor T. Yamazaki. This work is supported by the Grant-in-Aid of the Japanese Ministry of Education, Culture and Science. 相似文献
994.
Emission spectra of the CN violet band system (B2Σ—X2Σ) were observed by the electron impact on HCN with several impact energies near the threshold. The formation of CN(B) by the dissociative excitation of HCN was investigated. The threshold energy agreed essentially with that obtained by the photodissociation measurements by Okabe et al. The excitation function and the dependence of the vibrational populations of CN(B) on the electron energy were obtained. These results suggest that an optically allowed state contributes to the formation of CN(B) from HCN as a main precursor. 相似文献
995.
Yamada T Inoue T Yamada K Takano N Osaka T Harada H Nishiyama K Taniguchi I 《Journal of the American Chemical Society》2003,125(26):8039-8042
High-resolution electron energy loss spectroscopy (HREELS) yielded evidence for the formation of single covalent bonds between Si(111) surface atoms and CH(3) groups from the reaction of CH(3)MgBr and hydrogen-terminated H:Si(111)(1 x 1). The vibration at 678 cm(-)(1), assigned to the C-Si bond, was isolated within the spectrum of CH(3) on deuterium-terminated D:Si(111)(1 x 1). The CH(3) groups were thermally stable at temperatures below 600 K. The C-Si bonds are essential for enhancing the usefulness of alkyl moieties, which will lead to a new prospective technology of nanoscale fabrication and biochemical application. 相似文献
996.
When activated at high temperature (873 K) doped lanthana such as La2O3, Ce2O3, Sm2O3 derived from nitrate showed remarkable effect on the MgO-supported ruthenium activity for ammonia synthesis. The activity
treated with hydrogen at 873 K became 5 times as active as that treated at 623 K. The activity levels were almost the same
as those of the Ru-lanthana (support) system under the same activation condition. It was thought that the lanthana was partly
reduced and a strong metal support interaction occurred. The partially reduced lanthana was thought to donate electrons to
the contacting Ru atoms forming the active centers. The other characters such as the stability were also discussed by comparing
with alkali promoters. 相似文献
997.
Stereospecific synthesis of urea-tethered neoglycoconjugates starting from glucopyranosyl carbamates
Silyl-assisted elimination reaction of glucopyranosyl carbamates has been established for the synthesis of α- and β-d-glucopyranosyl isocyanates and ureas. This method proved to be useful for the synthesis of urea-tethered neoglycoconjugates. 相似文献
998.
Two new mononuclear Ca(II) complexes with aryl dihydrogen phosphate ligands having two strategically oriented bulky amide groups, 2,6-(Ph3CCONH)2C6H3OPO3H2 (1), including one with a phosphate monoanion, (NMe4)[CaII[O2P(OH)OC6H3-2,6-(NHCOCPh3)2]3(NCMe)3] (3), and one with a phosphate dianion, [CaII[O3POC6H3-2,6-(NHCOCPh3)2](H2O)3(MeOH)2] (4). Both are analogues for the NH...O hydrogen bonds in the active site of Ca(II)-containing phosphotransferase. Crystallographic studies of these Ca(II) complexes revealed that the amide NHs are directed to uncoordinated O atoms of the phosphates, and the IR and 1H NMR spectra indicate that strong NH...O hydrogen bonds are formed only in the phosphate dianion state. The ligand exchange reaction of 3 with a non-hydrogen-bonded phosphate ligand shows that the NH...O hydrogen bonds prevent the Ca-O bond from dissociation. A scatter plot analysis comparing the distance of a Ca-O bond with the Ca-O-P angle, the Fourier density analysis, and DFT calculations reveal that a partial degree of covalency in the Ca-O(phosphate) bonds is present. 相似文献
999.
Takagi C Sukeda M Kim HS Wataya Y Yabe S Kitade Y Matsuda A Shuto S 《Organic & biomolecular chemistry》2005,3(7):1245-1251
5'-methylenearisteromycin 5 and its 2-fluoro derivative 6, which were designed as antimalarial agents because of their AdoHcy hydrolase inhibition, were synthesized from D-ribose, using a stereoselective intramolecular radical cyclization as the key step to construct the carbocyclic structure. These compounds were evaluated as AdoHcy hydrolase inhibitors with the recombinant human and malarial parasite enzymes. Although 5 and 6 were both potent inhibitors of the malarial parasite AdoHcy hydrolase, the 2-fluoro derivative 6 proved to be superior due to its lower inhibitory effect on the human enzyme. In addition, 6 was identified as a potent antimalarial agent using an in vitro assay system with Plasmodium falciparum. 相似文献
1000.
We designed two aromatic analogues 1a and 1b of macrolactin A with expectation of enhancing biological activity and metabolical stability. As a result of retrosynthetic analysis of these compounds 1a-b, two synthetic strategies have been examined. The first strategy includes the enantioselective addition of nonadienyl anion, derived from 3, to aldehyde 4 as a key step. The second one includes epimerization of ynone 7 to (E,E)-conjugated dienone 31 and subsequent diastereoselective hydride-reduction of 31. Although the former route furnished no desired target, the latter one was revealed to work well for the synthesis of 1. Unfortunately, the aimed (2Z,4E)-analogue 1a could not be synthesized due to an epimerization of the (2Z)-olefin into the (2E)-olefin. However, these methods could be applied to the total asymmetric synthesis of the (2E,4E)-analogue 1b. Overall, control of all of the four stereocenters was achieved by means of asymmetric and diastereoselective reactions without using any chiral natural sources. 相似文献