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  Chagosensine: A Riddle Wrapped in a Mystery Inside an Enigma

Heinrich, M., Murphy, J. J., Ilg, M. K., Letort, A., Flasz, J. T., Philipps, P., et al. (2020). Chagosensine: A Riddle Wrapped in a Mystery Inside an Enigma. Journal of the American Chemical Society, 142(13), 6409-6422. doi:10.1021/jacs.0c01700.

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 Creators:
Heinrich, Marc1, Author           
Murphy, John J.1, Author           
Ilg, Marina K.1, Author           
Letort, Aurélien1, Author           
Flasz, Jakub T.1, Author           
Philipps, Petra2, Author           
Fürstner, Alois1, Author           
Affiliations:
1Research Department Fürstner, Max-Planck-Institut für Kohlenforschung, Max Planck Society, ou_1445584              
2Service Department Farès (NMR), Max-Planck-Institut für Kohlenforschung, Max Planck Society, ou_1445623              

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 Abstract: The marine macrolide chagosensine is supposedly distinguished by a (Z,Z)-configured 1,3-chlorodiene contained within a highly strained 16-membered lactone ring, which also incorporates two trans-2,5-disubstituted tetrahydrofuran (THF) rings; this array is unique. After our initial synthesis campaign had shown that the originally proposed structure is incorrect, the published data set was critically revisited to identify potential mis-assignments. The “northern” THF ring and the anti-configured diol in the “southern” sector both seemed to be sites of concern, thus making it plausible that a panel of eight diastereomeric chagosensine-like compounds would allow the puzzle to be solved. To meet the challenge, the preparation of the required building blocks was optimized, and a convergent strategy for their assembly was developed. A key role was played by the cobalt-catalyzed oxidative cyclization of alken-5-ol derivatives (“Mukaiyama cyclization”), which is shown to be exquisitely chemoselective for terminal alkenes, leaving even terminal alkynes (and other sites of unsaturation) untouched. Likewise, a palladium-catalyzed alkyne alkoxycarbonylation reaction with formation of an α-methylene-γ-lactone proved instrumental, which had not found application in natural product synthesis before. Further enabling steps were a nickel-catalyzed “Tamaru-type” homocrotylation, stereodivergent aldehyde homologations, radical hydroindation, and palladium-catalyzed alkyne-1,2-bis-stannation. The different building blocks were assembled in a serial fashion to give the idiosyncratic chlorodienes by an unprecedented site-selective Stille coupling followed by copper-mediated tin/chlorine exchange. The macrolactones were closed under forcing Yamaguchi conditions, and the resulting products were elaborated into the targeted compound library. Yet, only one of the eight diastereomers turned out to be stable in the solvent mixture that had been used to analyze the natural product; all other isomers were prone to ring opening and/or ring expansion. In addition to this stability issue, our self-consistent data set suggests that chagosensine has almost certainly little to do with the structure originally proposed by the isolation team.

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Language(s): eng - English
 Dates: 2020-02-122020-03-062020-04-01
 Publication Status: Published in print
 Pages: 14
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1021/jacs.0c01700
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Title: Journal of the American Chemical Society
  Other : JACS
  Abbreviation : J. Am. Chem. Soc.
Source Genre: Journal
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Publ. Info: Washington, DC : American Chemical Society
Pages: - Volume / Issue: 142 (13) Sequence Number: - Start / End Page: 6409 - 6422 Identifier: ISSN: 0002-7863
CoNE: https://pure.mpg.de/cone/journals/resource/954925376870