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931.
Mariko Yoshida Tetsuhiro Nemoto Zengduo Zhao Yuta Ishige Yasumasa Hamada 《Tetrahedron: Asymmetry》2012,23(11-12):859-866
A novel catalytic asymmetric synthetic method for making spirocyclohexadienones with an all-carbon quaternary spirocenter was developed based on the Pd-catalyzed intramolecular ipso-Friedel–Crafts allylic alkylation of phenols. When 5 mol % of the Pd catalyst and 12 mol % of (?)-9-NapBN (?)-3e were used, the spirocyclic adduct was obtained with up to 93% ee, albeit with low chemical yield. On the other hand, when using 6 mol% of the Trost ligand (R,R)-3k, the spirocyclic adducts were obtained in good yields with up to 89% ee (diastereoselectivity = 9.2:1). 相似文献
932.
Asymmetric Total Synthesis of Heronamides A–C: Stereochemical Confirmation and Impact of Long‐Range Stereochemical Communication on the Biological Activity 下载免费PDF全文
Prof. Dr. Naoki Kanoh Shunya Itoh Kohei Fujita Dr. Kohei Sakanishi Ryosuke Sugiyama Yuta Terajima Prof. Dr. Yoshiharu Iwabuchi Prof. Dr. Shinichi Nishimura Prof. Dr. Hideaki Kakeya 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(25):8586-8595
Heronamides are biosynthetically related metabolites isolated from marine‐derived actinomycetes. Heronamide C shows potent antifungal activity by targeting membrane phospholipids possessing saturated hydrocarbon chains with as‐yet‐unrevealed modes of action. In spite of their curious hypothesized biosynthesis and fascinating biological activities, there have been conflicts in regard to the reported stereochemistries of heronamides. Here, we describe the asymmetric total synthesis of the originally proposed and revised structures of heronamide C, which unambiguously confirmed the chemical structure of this molecule. We also demonstrated nonenzymatic synthesis of heronamides A and B from heronamide C, which not only proved the postulated biosynthesis, but also confirmed the correct structures of heronamides A and B. Investigation of the structure–activity relationship of synthetic and natural heronamides revealed the importance of both long‐range stereochemical communication and the 20‐membered macrolactam ring for the biological activity of these compounds. 相似文献
933.
Understanding the mechanism of the oxygen reduction reaction over nonprecious metal catalysts is important for green and sustainable electrochemical energy conversion. This article presents our recent progress in kinetic studies using rotating ring-disk electrodes. We have established a mathematically and experimentally modified rotating ring-disk electrode approach to calculate the corresponding kinetic rate constants of the 4-e reduction of O2 to H2O (k1), the 2-e reduction of O2 to H2O2 (k2), and the 2-e reduction of H2O2 to H2O (k3). Furthermore, the overestimation of the 4-e reduction process, which derives from the (2 + 2)-e pathway in the catalyst layer matrix, was corrected by studying the effect of catalyst loading density. The established method has been successfully applied to the oxygen reduction reaction over Fe/N/C and N/C catalysts in acidic and alkaline media. 相似文献
934.
Shimazaki Kosuke Satoh Kozue Wagatsuma Kazuaki 《Plasma Chemistry and Plasma Processing》2017,37(4):1265-1279
Plasma Chemistry and Plasma Processing - This paper represents emission spectrometric analysis of a hollow-cathode glow discharge plasma with helium–oxygen mixed gas for surface treatment of... 相似文献
935.
Copper‐Mediated C6‐Selective Dehydrogenative Heteroarylation of 2‐Pyridones with 1,3‐Azoles 下载免费PDF全文
Riko Odani Dr. Koji Hirano Prof. Dr. Tetsuya Satoh Prof. Dr. Masahiro Miura 《Angewandte Chemie (International ed. in English)》2014,53(40):10784-10788
A copper‐mediated C6‐selective dehydrogenative heteroarylation of 2‐pyridones with 1,3‐azoles has been developed. The reaction proceeded smoothly by twofold C? H cleavage even in the absence of noble‐metal catalysts. The observed site selectivity was directed by a pyridyl substituent on the nitrogen atom of the pyridone ring. This directing group was readily removed after the coupling event, thus leading to 2‐pyridone derivatives with a free N? H group. Moreover, in some cases, catalytic turnover of the Cu salt was also possible with the ideal terminal oxidant: molecular oxygen in air. 相似文献
936.
C5–C10 Directly Bonded Tetrodotoxin Analogues: Possible Biosynthetic Precursors of Tetrodotoxin From Newts 下载免费PDF全文
Yuta Kudo Yoko Yamashita Prof. Dr. Dietrich Mebs Dr. Yuko Cho Prof. Dr. Keiichi Konoki Prof. Dr. Takeshi Yasumoto Prof. Dr. Mari Yotsu‐Yamashita 《Angewandte Chemie (International ed. in English)》2014,53(52):14546-14549
The identification of novel tetrodotoxin (TTX, 1 ) analogues would significantly contribute to the elucidation of its biosynthetic pathway. In this study, the first C5–C10 directly bonded TTX analogues, 4,9‐anhydro‐10‐hemiketal‐5‐deoxyTTX ( 2 ) and 4,9‐anhydro‐8‐epi‐10‐hemiketal‐5,6,11‐trideoxyTTX ( 3 ), were found in the newt Cynops ensicauda popei by using a screening method involving HILIC‐LC–MS/MS focused on the fragment ions of TTX analogues, and their structures were elucidated by spectroscopic methods. Compound 2 was detected in a wide range of newt species, and the 2 and TTX contents of 22 newt specimens were correlated (rs=0.88). Based on these results and its structural features, 2 was predicted to serve as a precursor of TTX that would be directly converted into 4,9‐anhydroTTX ( 4 ) by Baeyer–Villiger‐like oxidation or via 4,9‐anhydro‐5‐deoxyTTX formed by cleavage of the C5–C10 bond. The bicyclic carbon skeletons of 2 and 3 suggested a possible monoterpene origin for TTX. 相似文献
937.
Prof. Dr. Kenshu Fujiwara Yuki Suzuki Nao Koseki Yu‐ichi Aki Yuta Kikuchi Shun‐ichi Murata Fuyuki Yamamoto Mariko Kawamura Prof. Dr. Toshio Norikura Prof. Dr. Hajime Matsue Prof. Dr. Akio Murai Prof. Dr. Ryo Katoono Prof. Dr. Hidetoshi Kawai Prof. Dr. Takanori Suzuki 《Angewandte Chemie (International ed. in English)》2014,53(3):780-784
Pectenotoxin‐2 (PTX2) is a shellfish toxin and has a non‐anomeric spiroacetal, which is not stabilized by an anomeric effect. The selective construction of the non‐anomeric spiroacetal has been a major problem in the synthesis of PTX2. Described herein is the stereoselective total synthesis of PTX2 via the isomerization of anomeric spiroacetal pectenotoxin‐2b (PTX2b). The synthesis of PTX2b was achieved by a simple process including sulfone‐mediated assembly of spirocyclic and bicyclic acetals and subsequent macrocyclization by ring‐closing olefin metathesis. Finally, the selective construction of PTX2 was accomplished by the early termination of a dynamic transition process to equilibrium in the acid‐catalyzed isomerization of anomeric PTX2b. [6,6]‐Spiroacetal pectenotoxin‐2c (PTX2c) was also synthesized from PTX2b. The cytotoxicity assay of the synthetic compounds against HepG2 and Caco2 cancer cells showed a potency of the order: PTX2?PTX2b>PTX2c. 相似文献
938.
939.
Hiroki Toya Takahito Satoh Kentaro Okano Kiyosei Takasu Masataka Ihara Atsushi Takahashi Haruo Tanaka Hidetoshi Tokuyama 《Tetrahedron》2014
Total synthesis of (−)- and (+)-petrosin was accomplished. Stereocontrolled construction of the quinolizidine ring was achieved through a diastereoselective Mannich reaction and an aza-Michael reaction. Head-to-tail dimerization was performed by assembly of the two monomers using Suzuki–Miyaura cross coupling and subsequent ring-closing metathesis to construct the 16-membered ring. Biological evaluation of synthetic (−)- and (+)-petrosin and its derivatives indicated that the bispiperidine structure was necessary for the inhibition of syncytium formation. 相似文献
940.
Objective: The aim of this study was to apply a novel method to measure excitation-contraction coupling time (ECCT) in normal soleus muscles. Methods: We performed simultaneous recordings of soleus compound muscle action potential (CMAP) and foot movement-related potential (MRP), and measured ankle plantar flexion torque in 36 healthy subjects. We calculated ECCT and examined the relations between CMAP, MRP, ECCT and ankle plantar flexion torque. Results: Statistical analyses established reference ranges (mean ± SE) for CMAP (13.4 ± 0.9 mV), MRP (5.3 ± 0.4 m/s2), ECCT (5.2 ± 0.1 ms), torque (85.9 ± 6.4 Nm) and torque/body weight (1.4 ± 0.1 Nm/kg). The torque showed a positive linear correlation with CMAP (p = 0.041) and a negative linear correlation with ECCT (p = 0.045). Conclusion: Soleus ECCT can be recorded easily, and is useful to assess the impairment of E-C coupling in muscles of the lower extremities. 相似文献