Details of a Researcher - Takao, Ken-ichi

Papers - Takao, Ken-ichi

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Studies toward the synthesis of perforatumone: Synthesis of the 7-OXABICYCLO[4.2.1]NONANE-8,9-DIONE CORE

Nakajima T., Takiguchi K., Yoshida K., Ogura A., Takao K.

Heterocycles (Heterocycles) 99 ( 1 ) 661 - 668 2019

ISSN 03855414

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Total Syntheses of (+)-Aquatolide and Related Humulanolides

Takao K., Kai H., Yamada A., Fukushima Y., Komatsu D., Ogura A., Yoshida K.

Angewandte Chemie - International Edition (Angewandte Chemie - International Edition) 58 ( 29 ) 9851 - 9855 2019

ISSN 14337851

© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim The short, efficient total synthesis of (+)-aquatolide was achieved by a biomimetic transannular [2+2] photocycloaddition, and provides the first example of constructing a 5/5/4/8-ring system from asteriscunolides. Furthermore, the reaction leading to a 5/4/4/7-ring system, the originally proposed structure of aquatolide, was also developed. This strategy achieved syntheses of five more humulanolides, (−)-asteriscunolides A, C, D, and I, and (+)-tetradehydroasteriscanolide.

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Identification of topoisomerases as molecular targets of cytosporolide C and its analog

Otake K., Yamada K., Miura K., Sasazawa Y., Miyazaki S., Niwa Y., Ogura A., Takao K., Simizu S.

Bioorganic and Medicinal Chemistry (Bioorganic and Medicinal Chemistry) 27 ( 15 ) 3334 - 3338 2019

ISSN 09680896

© 2019 Elsevier Ltd Cytosporolide (Cytos) A–C, isolated from the fungus Cytospora sp., have anti-microbial activity, but their molecular targets in mammalian cells are unknown. We have previously reported the total synthesis of Cytos A by biomimetic hetero-Diels-Alder reaction. In this study, to examine the novel bioactivity of Cytos, we synthesized Cytos C and measured cell growth-inhibiting activities of 7 compounds, including Cytos A and C, in several human cancer cell lines. Among these compounds, Cytos C and tetradeoxycytosporolide A (TD-Cytos A), a model compound for the synthesis of Cytos A, had anti-proliferative effects on cancer cells, and TD-Cytos A exhibited stronger activity than Cytos C. In vitro topoisomerase-mediated DNA relaxing experiments showed that TD-Cytos A inhibited the activities of topoisomerase I and II, whereas Cytos C targeted only topoisomerase I. These data suggest that the anti-proliferative activities of Cytos correlate with the inhibition of topoisomerases and implicated TD-Cytos A as a novel anti-cancer drug that suppresses the activities of topoisomerase I and II.

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Enantioselective Total Synthesis of (-)-Misramine

Yoshida K., Fujino Y., Takamatsu Y., Matsui K., Ogura A., Fukami Y., Kitagaki S., Takao K.

Organic Letters (Organic Letters) 20 ( 16 ) 5044 - 5047 2018.08

ISSN 15237060

© 2018 American Chemical Society. The enantioselective total synthesis of an unusual pentacyclic proaporphine alkaloid, (-)-misramine, was achieved. The synthetic strategy relied on an enantioselective intramolecular Friedel-Crafts-type 1,4-addition using an asymmetric organocatalyst to construct a spiroindane skeleton containing an all-carbon quaternary stereocenter and a double reductive amination of the keto-aldehyde to form a piperidine ring toward the end of the synthesis. This work is the first example of asymmetric synthesis of a proaporphine alkaloid.

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Total Synthesis of Clavilactones

Ken-ichi Takao, Kento Mori, Kenya Kasuga, Ryuki Nanamiya, Ayumi Namba, Yuuki Fukushima, Ryuichi Nemoto, Takuma Mogi, Hiroyuki Yasui, Akihiro Ogura, Keisuke Yoshida, and Kin-ichi Tadano

J. Org. Chem. (Journal of Organic Chemistry) Vol.83 ( 13 ) 7060 - 7075 2018.07

Research paper (scientific journal), Joint Work, Accepted, ISSN 00223263

Copyright © 2018 American Chemical Society. Clavilactones A, B, and D are epidermal growth factor receptor tyrosine kinase inhibitors that were isolated from cultures of the fungus Clitocybe clavipes. Here, we report full details of the total synthesis of these clavilactones. A key feature of our synthetic approach is a ring-opening/ring-closing metathesis strategy that allows the concise transformation of a cyclobutenecarboxylate into a γ-butenolide. Coupled with enantioselective Ti/BINOL-catalyzed alkynylation of a multisubstituted benzaldehyde and ring-closing metathesis of a diene-bearing silylene acetal to construct the 10-membered carbocycle, this strategy enabled the total synthesis of the natural enantiomers (+)-clavilactone A and (-)-clavilactone B. In addition, the correct structure of clavilactone D was determined by the synthesis of two newly proposed structures. This research resulted in the asymmetric synthesis of the revised (+)-clavilactone D.

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Synthesis and Evaluation of Biological Activities of Vibsanin A Analogs

Wataru Matsuki, So Miyazaki, Keisuke Yoshida, Akihiro Ogura, Yukiko Sasazawa, Ken-ichi Takao, and Siro Simizu

Bioorg. Med. Chem. Lett. Vol.27 4536 - 4539 2017.10