TY - JOUR
T1 - Stereospecific β-l-Rhamnopyranosylation through an SNi-Type Mechanism by Using Organoboron Reagents
AU - Nishi, Nobuya
AU - Sueoka, Kazuhiro
AU - Iijima, Kiyoko
AU - Sawa, Ryuichi
AU - Takahashi, Daisuke
AU - Toshima, Kazunobu
PY - 2018/10/15
Y1 - 2018/10/15
N2 - 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-Rhap) with complete stereoselectivity in moderate to high yields without any further additives under mild conditions. Mechanistic studies of the borinic ester mediated glycosylation using 13C kinetic isotope effect (KIE) measurements and DFT calculations were consistent with a concerted SNi mechanism with an exploded transition state. In addition, the present glycosylation method was applied successfully to the synthesis of a trisaccharide, α-l-Rhap-(1,2)-β-l-Rhap-(1,4)-Glcp, derived from Streptococcus pneumoniae serotypes 7B, 7C, and 7D.
AB - 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-Rhap) with complete stereoselectivity in moderate to high yields without any further additives under mild conditions. Mechanistic studies of the borinic ester mediated glycosylation using 13C kinetic isotope effect (KIE) measurements and DFT calculations were consistent with a concerted SNi mechanism with an exploded transition state. In addition, the present glycosylation method was applied successfully to the synthesis of a trisaccharide, α-l-Rhap-(1,2)-β-l-Rhap-(1,4)-Glcp, derived from Streptococcus pneumoniae serotypes 7B, 7C, and 7D.
KW - carbohydrates
KW - glycosylation
KW - organoboron reagents
KW - stereoselectivity
KW - β-l-rhamnosylation
UR - http://www.scopus.com/inward/record.url?scp=85053662599&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85053662599&partnerID=8YFLogxK
U2 - 10.1002/anie.201808045
DO - 10.1002/anie.201808045
M3 - Article
C2 - 30098095
AN - SCOPUS:85053662599
VL - 57
SP - 13858
EP - 13862
JO - Angewandte Chemie - International Edition
JF - Angewandte Chemie - International Edition
SN - 1433-7851
IS - 42
ER -