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81.
The mechanisms of the Myers-Saito cyclization and the Schmittel cyclization of hepta-1,2,4-triene-6-yne are studied by ab initio multireference MO methods (CASSCF and MRMP2 methods). For the Myers-Saito cyclization, two transition states with C(s) and C? symmetries are located. The transition state with C1 symmetry is only 1.5 kcal/mol lower in energy than that with C(s) symmetry at the MRMP2 calculation level. The obtained activation energy at the transition state with C? symmetry and the reaction energy are 16.6 and 16.2 kcal/mol exothermic, respectively. For the Schmittel cyclization, two transition states with C(s) and C? symmetry are also obtained. The transition state with C? symmetry is 7.9 kcal/mol lower in energy than that with C(s) symmetry. The transition state with C? symmetry for Schmittel cyclization is 6.7 kcal/mol higher in energy than that for the Myers-Saito cyclization. The reaction mechanisms are analyzed by a CiLC-IRC method. The interactions of orbitals for the Myers-Saito and Schmittel cyclizations can be distinguished. 相似文献
82.
Four formyl-group-carrying thioaminyl radicals were generated, and one radical could be isolated as radical crystals. Magnetic susceptibility measurements of the isolated radical showed a ferromagnetic regular linear-chain interaction of 2J/k(B) = 3.2 K, which was explained in terms of the X-ray crystallographic results. 相似文献
83.
Lee PS Sakai S Hörstermann P Roth WR Kallel EA Houk KN 《Journal of the American Chemical Society》2003,125(19):5839-5848
The allowed conrotatory cyclobutene ring-opening has a distinctly nonplanar carbon skeleton. Classic experiments by Brauman and Archie, and by Freedman et al., placed the allowed/forbidden gap at greater than 15 kcal/mol. Wolfgang Roth proposed that a system forced to planarity might have a smaller preference for the conrotatory mode than unconstrained systems. Such systems have now been studied theoretically and experimentally, and results that confirm Roth's postulate are presented here. The experiments were performed in Bochum, and the calculations were carried out in Osaka and Los Angeles. As the cyclobutene ring-opening transition structure approaches planarity, the energy gap between allowed conrotatory and the forbidden disrotatory pathways decreases. For the ring-opening of a cyclobutene fused to norbornene, the energy gap between the forbidden and the allowed transition state is only 4.1 kcal/mol by CASSCF and 8.0 kcal/mol by CAS-MP2 as compared to 13.4 and 19.2 kcal/mol, respectively, for the parent cyclobutene. Experimental studies of 3,4-dimethylcyclobutenes fused to various ring systems are reported, and a trend is found toward a reduced allowed/forbidden gap as the planarity of the cyclobutene is enforced. 相似文献
84.
Irinotecan or 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin (CPT-11) is an anticancer pro-drug used in the treatment of many types of cancer. We describe here the validation of an analytical method for CPT-11 and its metabolites, including an active metabolite, 7-ethyl-10-hydroxycamptothecin (SN-38), its glucuronidated form, SN-38G, and several cytochrome P450 3A-mediated products such as 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino]carbonyloxycamptothecin (APC) using a high-performance liquid chromatography connected to parallel fluorescence and mass spectrometry detection systems. This method is characterized as follows: (1) simple extraction of the analytes from biomaterials with perchloric acid/methanol; (2) sensitive quantitation of major metabolites (SN-38G, SN-38 and APC) with a fluorescence detector (FLD), where the limits of quantitation by FLD were 2.5 ng/mL for SN-38G and APC, 5 ng/mL for CPT-11 and 1 ng/mL for SN-38, respectively; (3) parallel selective monitoring of the metabolites including minor metabolites with a mass selected detector (MSD). There was no observed interference by other drugs expected to be co-administered. This method showed its usefulness by identifying a novel metabolite produced in human hepatic microsomes. The results indicate that this combination of FLD and MSD enables a highly selective analysis of CPT-11 and its metabolites, and is useful for studies both in vivo and in vitro. 相似文献
85.
Yoshihiro Ushigoe Shogo Tanaka Masatomo Nojima Kevin J. McCullough 《Tetrahedron letters》1994,35(52):9741-9744
-Hydroperoxyisochroman derivatives 5 react with formaldehyde under acidic conditions to produce mixtures of bicyclic 1,2,4,6-tetroxepane 9 and 1,2,4,6,8-pentoxonane 10 derivatives. The structure of the compound 10a was unambiguously established by the X-ray analysis. With acetaldehyde, only the corresponding 1,2,4,6-tetroxepanes 9 were obtained. 相似文献
86.
Qi Xue Bryan Kit Yue Ng Ho Wing Man Tai-Sing Wu Yun-Liang Soo Molly Mengjung Li Shogo Kawaguchi Kwok Yin Wong Shik Chi Edman Tsang Bolong Huang Tsz Woon Benedict Lo 《Chemical science》2021,13(1):50
Precisely tuning the nuclearity of supported metal nanoclusters is pivotal for designing more superior catalytic systems, but it remains practically challenging. By utilising the chemical and molecular specificity of UiO-66-NH2 (a Zr-based metal–organic framework), we report the controlled synthesis of supported bi- and trinuclear Cu-oxo nanoclusters on the Zr6O4 nodal centres of UiO-66-NH2. We revealed the interplay between the surface structures of the active sites, adsorption configurations, catalytic reactivities and associated reaction energetics of structurally related Cu-based ‘single atoms’ and bi- and trinuclear species over our model photocatalytic formic acid reforming reaction. This work will offer practical insight that fills the critical knowledge gap in the design and engineering of new-generation atomic and nanocluster catalysts. The precise control of the structure and surface sensitivities is important as it can effectively lead to more reactive and selective catalytic systems. The supported bi- and trinuclear Cu-oxo nanoclusters exhibit notably different catalytic properties compared with the mononuclear ‘Cu1’ analogue, which provides critical insight for the engineering of more superior catalytic systems.The controlled synthesis of novel bi- and trinuclear Cu-oxo nanoclusters supported on UiO-66-NH2 that show notably different catalytic properties in the photocatalytic formic acid decomposition reaction is reported. 相似文献
87.
Kazuhira Miwa Shinobu Aoyagi Takahiro Sasamori Shogo Morisako Hiroshi Ueno Yutaka Matsuo Hideki Yorimitsu 《Molecules (Basel, Switzerland)》2022,27(2)
The reduction of fullerene (C60) with sodium dispersion in the presence of an excess amount of dipropyl sulfate was found to yield highly propylated fullerene, C60(nC3H7)n (max. n = 24), and C60(nC3H7)20 was predominantly generated as determined by mass spectroscopy. 相似文献
88.
Keisuke Fukumura Yuki Narimatsu Shogo Moriwaki Eiko Iwakoshi-Ukena Megumi Furumitsu Kazuyoshi Ukena 《Molecules (Basel, Switzerland)》2021,26(19)
We previously identified a novel small hypothalamic protein, neurosecretory protein GL (NPGL), which induces feeding behavior and fat accumulation in rodents depending on their diet. In the present study, we explored the effects of NPGL on feeding behavior and energy metabolism in mice placed on a long-term high-fat diet with 60% calories from fat (HFD 60). Overexpression of the NPGL precursor gene (Npgl) over 18 weeks increased food intake and weight. The weekly weight gain of Npgl-overexpressing mice was higher than that of controls until 7 weeks from induction of overexpression, after which it ceased to be so. Oral glucose tolerance tests showed that Npgl overexpression maintained glucose tolerance and increased blood insulin levels, and intraperitoneal insulin tolerance tests showed that it maintained insulin sensitivity. At the experimental endpoint, Npgl overexpression was associated with increased mass of the perirenal white adipose tissue (WAT) and decreased mass of the epididymal WAT (eWAT), resulting in little effect on the total WAT mass. These results suggest that under long-term HFD 60 feeding, Npgl overexpression may play a role in avoiding metabolic disturbance both by accelerating energy storage and by suppressing excess fat accumulation in certain tissues, such as the eWAT. 相似文献
89.
90.