Boronic-Acid-Catalyzed Regioselective and 1,2- cis -Stereoselective Glycosylation of Unprotected Sugar Acceptors via SNi-Type Mechanism

Masamichi Tanaka, Akira Nakagawa, Nobuya Nishi, Kiyoko Iijima, Ryuichi Sawa, Daisuke Takahashi, Kazunobu Toshima

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Abstract

Regio- and 1,2-cis-stereoselective chemical glycosylation of unprotected glycosyl acceptors has been in great demand for the efficient synthesis of natural glycosides. However, simultaneously regulating these selectivities has been a longstanding problem in synthetic organic chemistry. In nature, glycosyl transferases catalyze regioselective 1,2-cis-glycosylations via the SNi mechanism, yet no useful chemical glycosylations based on this mechanism have been developed. In this paper, we report a highly regio- and 1,2-cis-stereoselective SNi-type glycosylation of 1,2-anhydro donors and unprotected sugar acceptors using p-nitrophenylboronic acid (10e) as a catalyst in the presence of water under mild conditions. Highly controlled regio- and 1,2-cis-stereoselectivities were achieved via the combination of boron-mediated carbohydrate recognition and the SNi-type mechanism. Mechanistic studies using the KIEs and DFT calculations were consistent with a highly dissociative concerted SNi mechanism. This glycosylation method was applied successfully to the direct glycosylation of unprotected natural glycosides and the efficient synthesis of a complex oligosaccharide with minimal protecting groups.

Original languageEnglish
Pages (from-to)3644-3651
Number of pages8
JournalJournal of the American Chemical Society
Volume140
Issue number10
DOIs
Publication statusPublished - 2018 Mar 14

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ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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