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Stereospecific β‐ l ‐Rhamnopyranosylation through an S N i‐Type Mechanism by Using Organoboron Reagents
Author(s) -
Nishi Nobuya,
Sueoka Kazuhiro,
Iijima Kiyoko,
Sawa Ryuichi,
Takahashi Daisuke,
Toshima Kazunobu
Publication year - 2018
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201808045
Subject(s) - stereospecificity , chemistry , glycosylation , stereoselectivity , reagent , kinetic isotope effect , glycosyl donor , trisaccharide , stereochemistry , catalysis , organic chemistry , glycosyl , biochemistry , physics , deuterium , quantum mechanics
Stereospecific β‐ l ‐rhamnopyranosylations were conducted using a 1,2‐anhydro‐ l ‐rhamnopyranose donor and mono‐ol or diol acceptors in the presence of a glycosyl‐acceptor‐derived borinic or boronic ester. Reactions proceeded smoothly to provide the corresponding β‐ l ‐rhamnopyranosides (β‐ l ‐Rha p ) with complete stereoselectivity in moderate to high yields without any further additives under mild conditions. Mechanistic studies of the borinic ester mediated glycosylation using 13 C kinetic isotope effect (KIE) measurements and DFT calculations were consistent with a concerted S N i mechanism with an exploded transition state. In addition, the present glycosylation method was applied successfully to the synthesis of a trisaccharide, α‐ l ‐Rha p ‐(1,2)‐β‐ l ‐Rha p ‐(1,4)‐Glc p , derived from Streptococcus pneumoniae serotypes 7B, 7C, and 7D.