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21.
22.
Haruaki Ishiyama 《Tetrahedron》2006,62(1):166-170
An asymmetric synthesis of a diastereomer (2) of the structure (1) proposed for amphidinolide A, a cytotoxic macrolide from the cultured dinoflagellate Amphidinium sp., has been accomplished. The absolute configuration of amphidinolide A was established as 3 from comparison of NMR data, HPLC analysis, and [α]D values of amphidinolide A, and comparison with the synthetic diastereomers 2 and 3, the latter of which was synthesized previously by Trost's group. 相似文献
23.
Since 1999, direct borylation of hydrocarbons catalyzed by a transition metal complex has been extensively studied by several groups and has become an economical, efficient, elegant, and environmentally benign protocol for the synthesis of a variety of organoboron compounds. Re-, Rh-, Ir- and Pd-catalyzed C---H borylation of alkanes, arenes and benzylic positions of alkylarenes by bis(pinacolato)diboron or pinacolborane provide alkyl-, aryl-, heteroaryl- and benzylboron compounds, respectively. In this review, seminal early works and exciting recent developments in the area of direct borylation of hydrocarbons via C---H activation are summarized. 相似文献
24.
Masashi TsudaKohei Nozawa Kazutaka ShimboHaruaki Ishiyama Eri FukushiJun Kawabata Jun'ichi Kobayashi 《Tetrahedron letters》2003,44(7):1395-1399
The absolute configurations at five chiral centers, except for C-32(S) reported previously, in iejimalide B (1), a potent cytotoxic 24-membered macrolide isolated from a tunicate Eudistoma cf. rigida, were assigned as 4R, 9S, 17S, 22S, and 23S on the basis of detailed analysis of NMR data and chemical means. Furthermore, the structure of iejimalide B was revised from 2 (original: 13E) to its 13Z-isomer (1). 相似文献
25.
A new dimeric sesquiterpenoid with two eudesmane skeletons through a urea linkage, halichonadin A (1), as well as three new eudesmane sesquiterpenoids having a carbamate, an isonitrile, or an amino functionality, halichonadins B (2), C (3), and D (4), respectively, have been isolated from a marine sponge Halichondria sp., and the gross structures and relative stereochemistry of 1-4 were elucidated on the basis of spectral data and chemical means. 相似文献
26.
Treatment of N-(2-methyl-2-propenyl)-N-methyl-α-(methylsulfinyl)acetamide () with trifluoroacetic anhydride caused the cationic olefin cyclization through a Pummerer reaction intermediate to give the six-membered lactams and . Similar reaction converted N-2-butenyl-N-methyl-a-(methylsulfinyl)acetamide () to the five-membered lactam , and N-2-propenyl-N-methyl-α-(methylsulfinyl)- acetamide () to the five-membered lactams and . 相似文献
27.
28.
The modulation frequency characteristics of an erbium-doped fiber amplifier are analyzed theoretically and experimentally for various values of modulation frequency. The theoretical predictions by the approximate equations in the low and high frequency modulation and that by the Runge-Kutta method for all modulation frequencies are in good agreement with the experimental results. In the low frequency modulation, the population inversion is depleted because of the saturation effect due to the instantaneous power of the incident light, and a distorted output is obtained without phase delay. In the high frequency modulation, the linear amplification is obtained with the gain depletion determined by the time averaged power of the incident signal. In the intermediate frequency modulation, the highly distorted output is obtained with phase delay. 相似文献
29.
M. Mazzocco C. Signorini M. Romoli R. Bonetti A. De Francesco A. De Rosa M. Di Pietro L. Fortunato T. Glodariu A. Guglielmetti G. Inglima T. Ishikawa H. Ishiyama R. Kanungo N. Khai S. Jeong M. La Commara B. Martin H. Miyatake T. Motobayashi T. Nomura D. Pierroutsakou M. Sandoli F. Soramel L. Stroe I. Sugai M. H. Tanaka E. Vardaci Y. Watanabe A. Yoshida K. Yoshida 《The European physical journal. Special topics》2007,150(1):37-40
The elastic scattering process for 11Be ions impinging on
a 209Bi target was studied in the energy range around the
Coulomb barrier. The angular distributions of the 11Be scattered
particles were analyzed within the optical model framework in order
to evaluate the reaction cross section, which turned out to be much larger
than the fusion one, especially in the sub-barrier region. The comparison
with the system 9Be + 209Bi showed that the reaction cross section
is larger for the reaction 11Be + 209Bi in the energy range around
the Coulomb barrier, while they are rather similar at higher bombarding energies.
This result suggests that direct processes related to the 11Be
halo structure and lower binding energy are more relevant
at near-barrier energies. 相似文献
30.
Asymmetric Total Synthesis of Indole Alkaloids Containing an Indoline Spiroaminal Framework
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Dr. Takeshi Yamada Dr. Tetsuya Ideguchi‐Matsushita Dr. Tomoyasu Hirose Dr. Tatsuya Shirahata Dr. Rei Hokari Dr. Aki Ishiyama Dr. Masato Iwatsuki Dr. Akihiro Sugawara Dr. Yoshinori Kobayashi Dr. Kazuhiko Otoguro Prof. Satoshi Ōmura Prof. Toshiaki Sunazuka 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(33):11855-11864
The total synthesis of the indole alkaloids, neoxaline, oxaline and meleagrin A, all containing a unique indoline spiroaminal framework, was accomplished through the stereoselective introduction of a reverse prenyl group to the congested benzylic carbon of furoindoline, a two‐pot transformation of indoline (containing three nitrogen atoms at appropriate positions) to the featured indoline spiroaminal framework, and elimination of carbonate assisted by the adjacent imidazole moiety to construct the (E)‐dehydrohistidine. The absolute stereochemistry of neoxaline was elucidated through our total synthesis. In addition, we evaluated the bioactivity, especially the anti‐infectious properties, of neoxaline and oxaline, and of some synthetic intermediates. 相似文献