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 PPh₃ effectively proceeded under mild conditions to provide the corresponding 2-deoxy-2-iodoglycosides in high yields. The reactivity of the iodoglycosylations with PPh₃ 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 P­(OPh)₃ 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_Ni‑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_Ni 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_Ni-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_Ni-type mechanism. Mechanistic studies using the KIEs and DFT calculations were consistent with a highly dissociative concerted S_Ni 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 B₂

The first total synthesis of vineomycin B₂ (<b>1</b>) has been accomplished. The aglycon segment, a vineomycinone B₂ 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>