7 research outputs found
1,2-<i>cis</i>-α-Stereoselective Glycosylation Utilizing a Glycosyl-Acceptor-Derived Borinic Ester and Its Application to the Total Synthesis of Natural Glycosphingolipids
1,2-<i>cis</i>-α-Stereoselective glycosylations
were conducted using a 1,2-anhydroglucose donor and mono-ol acceptors
in the presence of a glycosyl-acceptor-derived borinic ester. Reactions
proceeded smoothly under mild conditions to provide the corresponding
α-glycosides with high stereoselectivity in moderate to high
yields. In addition, the present method was applied successfully to
the direct glycosylation of a protected ceramide acceptor and the
total synthesis of natural glycosphingolipids (GSLs)
Glycosylations of Glycals using <i>N</i>‑Iodosuccinimide (NIS) and Phosphorus Compounds for Syntheses of 2‑Iodo- and 2‑Deoxyglycosides
The glycosylations
of glycals and alcohols using <i>N</i>-iodosuccinimide (NIS)
and a catalytic amount of PPh<sub>3</sub> effectively
proceeded under mild conditions to provide the corresponding 2-deoxy-2-iodoglycosides
in high yields. The reactivity of the iodoglycosylations with PPh<sub>3</sub> significantly increased in comparison to that using NIS alone
as an activator. In addition, the glycosylations of glycals and alcohols
using catalytic amounts of NIS and PÂ(OPh)<sub>3</sub> were effectively
realized to give the corresponding 2-deoxyglycosides in high yields
Glycosyl-Acceptor-Derived Borinic Ester-Promoted Direct and β‑Stereoselective Mannosylation with a 1,2-Anhydromannose Donor
β-Stereoselective
mannosylations were conducted using a 1,2-anhydromannose
donor and mono-ol acceptors in the presence of a glycosyl-acceptor-derived
borinic ester. Reactions proceeded smoothly under mild conditions
to provide the corresponding β-mannosides with high stereoselectivity
in moderate to high yields. In addition, the present glycosylation
method was applied successfully to the total synthesis of acremomannolipin
A
Efficient and Stereoselective Synthesis of the Disaccharide Fragment of Incednine
Efficient and stereoselective synthesis of a disaccharide fragment, 2-deoxy-4-<i>O</i>-(<i>N</i>′-monodemethyl-d-forosaminyl)-2-methylamino-β-d-xylopyranoside, of a novel antibiotic, incednine (<b>1</b>), is described. The key β-stereoselective formation of a 2,3,4,6-tetradeoxy-4-methylamino glycoside bond was achieved by remote participation-assisted glycosylation
Systematic and Stereoselective Total Synthesis of Mannosylerythritol Lipids and Evaluation of Their Antibacterial Activity
The
total synthesis of the 20 homogeneous members of mannosylerythritol
lipids (MELs) with different alkyl chain lengths was effectively and
systematically accomplished from a strategically designed common key
intermediate that was stereoselectively constructed by the borinic
acid catalyzed β-mannosylation reaction. In addition, their
antibacterial activities against Gram-positive bacteria were evaluated.
Our results demonstrated that not only the length of the alkyl chains
but also the pattern of Ac groups on the mannose moiety were important
factors for antibacterial activity
Boronic-Acid-Catalyzed Regioselective and 1,2-<i>cis</i>-Stereoselective Glycosylation of Unprotected Sugar Acceptors via S<sub>N</sub>i‑Type Mechanism
Regio- and 1,2-<i>cis</i>-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-<i>cis</i>-glycosylations via the S<sub>N</sub>i mechanism, yet no useful chemical glycosylations based on
this mechanism have been developed. In this paper, we report a highly
regio- and 1,2-<i>cis</i>-stereoselective S<sub>N</sub>i-type
glycosylation of 1,2-anhydro donors and unprotected sugar acceptors
using <i>p</i>-nitrophenylboronic acid (<b>10e</b>) as a catalyst in the presence of water under mild conditions. Highly
controlled regio- and 1,2-<i>cis</i>-stereoselectivities
were achieved via the combination of boron-mediated carbohydrate recognition
and the S<sub>N</sub>i-type mechanism. Mechanistic studies using the
KIEs and DFT calculations were consistent with a highly dissociative
concerted S<sub>N</sub>i 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
Total Synthesis of Vineomycin B<sub>2</sub>
The
first total synthesis of vineomycin B<sub>2</sub> (<b>1</b>)
has been accomplished. The aglycon segment, a vineomycinone B<sub>2</sub> derivative, and the glycon segment, an α-l-acurosyl-l-rhodinose derivative, were prepared via C-glycosylation
using an unprotected sugar and powerful chemoselective O-glycosylation
using a 2,3-unsaturated sugar, respectively, as the key steps. Furthermore,
effective and simultaneous introduction of the two glycon moieties
to the aglycon part by concentration-controlled glycosylation led
to the total synthesis of <b>1</b>