NIS/H2SO4–Silica: a mild and efficient reagent system for the hydrolysis of thioglycosides

Glycosyl o-[1-(p-MeO-Phenyl)vinyl]benzoates (PMPVB) as Easily Accessible, Stable, and Reactive Glycosyl Donors for O-, S-, and C-Glycosylations under Brønsted Acid Catalysis

Methods suitable for the synthesis of both O- and S-glycosylations are relatively rare because commonly used promoters like halonium sources or gold catalysts are incompatible with thiols as nucleophiles. Here, we present (p-MeO)phenylvinylbenzoates (PMPVB) as easily accessible, stable, and reactive alkene-based glycosyl donors that can be activated with catalytic amounts of a Brønsted acid. This activation protocol not only allows us to synthesize O-glycosides but also can successfully provide S- and C-linked glycosides. The armed and disarmed donors lead to product formation in 5 min, showcasing the high reactivity of the donors. Competitive experiments show that the PMPVB donors are much more reactive than the corresponding PVB donors even under NIS/TMSOTf conditions, whereas PVB donors are not reactive enough to be efficiently activated under Brønsted acid conditions. The potential of the catalytic glycosylation protocol has also been showcased by synthesizing trisaccharides. The Brønsted acid activation of PMPVB donors also allows access to C-glycosides in a stereoselective fashion. The easy accessibility of the donor aglycon on a multigram scale in just two steps makes the PMPVB donors highly attractive alternatives.

Chemical synthesis of the 4-amino-4,6-dideoxy-d-glucose containing pentasaccharide repeating unit of the O-specific polysaccharide from Aeromonas hydrophila strain K691 in the form of its 2-aminoethyl glycoside

Chemical synthesis of the pentasaccharide repeating unit of the O-specific polysaccharide from Aeromonas hydrophilastrain K691 is reported. Synthesis of the pentasaccharide is accomplished by using a common disaccharide in sequence and finally attaching the rare sugar unit. The target structure was made in the form of its 2-aminoethyl glycoside which is essential for further glycconjugate formation. Stereoselective glycosylations were achieved by the activation of thioglycosides in the presence of H₂SO₄-silica in conjunction with N-iodosuccinimide.

Chemical synthesis of the hexasaccharide related to the repeating unit of the capsular polysaccharide from carbapenem resistant Klebsiella pneumoniae 2796 and 3264

Total synthesis of the hexasaccharide repeating unit of the capsular polysaccharide fromKlebsiella pneumoniae2796 and 3264 following a linear sequential glycosylation strategy.

Convergent chemical synthesis of the pentasaccharide repeating unit of the O-antigen from E. coli O158

Synthesis of the pentasaccharide repeating unit of the O-antigen fromE. coliO158 through a convergent [3 + 2] strategy is reported.

Convergent synthesis of the hexasaccharide related to the repeating unit of the O-antigen from E. coli O120

The hexasaccharide repeating unit of the O-antigen from E. coli O120 has been synthesized in the form of its 4-methoxyphenyl glycoside by a convergent [2 + 4] strategy.

Trichloroisocyanuric acid (TCCA): an efficient green reagent for activation of thioglycosides toward hydrolysis

Trichloroisocyanuric acid (TCCA), an inexpensive, commercially available, and non-toxic reagent has been used for the activation of thioglycosides toward their hydrolysis to the corresponding hemiacetals in high to excellent yields. The methodology provides a mild reaction condition for dealing with compounds containing acid sensitive functional groups.

A highly efficient deprotection of the 2,2,2-trichloroethyl group at the anomeric oxygen of carbohydrates

Commercially available zinc dust in the presence of ammonium chloride in acetonitrile at reflux removes the 2,2,2-trichloroethyl (TCE) group at anomeric centers with excellent yields (>95%) in short reaction times. This present method is easily implemented on substrates containing acyl and benzyl groups and large-scale reactions also proceed in high yield.

Zeolites and other silicon-based promoters in carbohydrate chemistry

Silicon-based materials, namely zeolites, clays, and silica gel have been widely used in organic synthesis, allowing mild reaction conditions and environmentally friendly methodologies. These heterogeneous catalysts are easy to handle, possess nontoxic and noncorrosive character and offer the possibility of recovery and reuse, thus contributing to clean and sustainable organic transformations. Moreover, they present shape-selective properties and provide stereo- and regiocontrol in chemical reactions. Herein, we survey the most significant applications of silicon-based materials as catalysts in carbohydrate chemistry, to mediate important transformations such as glycosylation, sugar protection and deprotection, and hydrolysis and dehydration. Emphasis is placed on their promising synthetic potential in comparison with conventional catalysts.