Nucleophilic allylation of N,O-acetals with allylic alcohols promoted by Pd/Et3B and Pd/Et2Zn systems

Pd/Et₃B and Pd/Et₂Zn systems promote the nucleophilic allylations of 2-aminotetrahydrofuran and 2-aminotetrahydropyran with allylic alcohols to provide ω-hydroxyhomoallylamines in high yields. The transformation is applicable to the allylation of non-protective carbohydrates, such as ribose and deoxyribose.     

Synthesis of new carbohydrate-derived ketones as organocatalysts in the enantioselective epoxidation of arylalkenes. Part 2: Chiral ketones from sugars

A range of new, somewhat complex, stereochemically varied, and structurally related carbohydrate-derived ketones were synthesised by a simple method from the carbohydrate precursor (d-gluco and d-galacto derivatives). The common skeleton possesses the keto function sited on a seven-membered ring fused to positions 2 and 3 of the sugar moiety. Their chirality transfer capability in the dioxirane-mediated epoxidation of arylalkenes was evaluated.     

Concise synthesis of Bacillusanthracis exosporium tetrasaccharide via two-stage activation of allyl glycosyl donor strategy

A highly efficient glycosylation protocol recently developed in our laboratory has been utilized in the short synthesis of the tetrasaccharide 1, an antigen important to the development of carbohydrate-based diagnostic tools and vaccines against anthrax. The protocol employs allyl glycosides as building blocks and improves the overall synthetic efficiency.     

Determination of post-culture processing with carbohydrates by MALDI-MS and TMS derivatization GC-MS

Biological materials generally require stabilization to retain activity or viability in a dry form. A number of industrial products, such as vaccines, probiotics and biopesticides have been produced as dry preparations. The same methods and materials used for stabilizing commercial microbial products may be applicable to preserving biothreat pathogens in a dry form. This is a likely step that may be encountered when looking at samples from terrorism attempts since only spores, such as those from Bacillus anthracis, are inherently stable when dried. The stabilizers for microbial preparations generally include one or more small carbohydrates. Different formulations have been reported for different industrial products and are often determined empirically. However sugar alcohols (mannitol and sorbitol) and disaccharides (lactose, sucrose and trehalose) are the common constituents of these formulations. We have developed an analytical method for sample preparation and detection of these simple carbohydrates using two complementary analytical tools, MALDI-MS and GC-MS. The native carbohydrates and other constituents of the formulation are detected by MALDI-MS as a screening tool. A longer and more detailed analysis is then used to specifically identify the carbohydrates by derivatization and GC-MS detection. Both techniques were tested against ten different types of stabilization recipes with Yersinia pestis cell mass cultured on different media types used as the biological component. A number of additional components were included in these formulations including proteins and peptides from serum or milk, polymers (e.g. poly vinyl pyrrolidone - PVP) and detergents (e.g. Tween). The combined method was characterized to determine several figures of merit. The accuracy of the method was 98% for MALDI-MS and 100% for GC-MS. The repeatability for detection of carbohydrates by MALDI-MS was determined to be 96%. The repeatability of compound identification by GC-MS was determined by monitoring variation in retention time, which is vital for identification of isomeric carbohydrates. The figures of merit illustrate an effective and accurate method for mono and disaccharide detection independent of formulation. This meets our primary goal for method development as small carbohydrates are among the most common stabilizers employed.     

Chemical Synthesis of an Octasaccharide Derivative Related to Group B Streptococcus Cell-Wall Polysaccharide

Group B Streptococcus (GBS) is the major pathogen that causes invasive infectious diseases in neonates and infants. The development of preventive and therapeutic strategies against GBS infection has been becoming the most pressing subject worldwide. Group B carbohydrate (GBC), the group B-specific polysaccharide that distinguishes GBS with other streptococci species, has been identified as an attractive antigen for diagnosis and vaccine development because of its highly conservative tetra-antennary structure. In this paper, a highly convergent [3 + 5] glycosylation strategy for efficient synthesis of an octasaccharide derivative related to GBC oligosaccharide unit II has been developed. In this synthesis, each glycosylation reaction was efficiently constructed with glycosyl imidates, especially trifluoroacetimidate, as donors, and each glycosidic bond was stereoselectively controlled via the neighboring group participation effect of acyl group on the 2-O-position of imidate donors or the solvent effect of Et₂O. Furthermore, the aminoethylphosphate group was smoothly installed on the 6-O-position of d -glucitol residue using the phosphoramidite method. After global deprotection, the target octasaccharide was successfully obtained from d -glucitol in 29 steps with an overall yield of 1.37%. The free amino group installed on the aminoethylphosphate spacer of the target molecule enables its modification with functionalized biomolecules for further biological studies.      

Rational Positioning of Metal Ions to Stabilize Open Tin Sites in Beta Zeolite for Catalytic Conversion of Sugars

Via hydrothermal synthesis of Sn-Al gels, mild dealumination and ion exchange, a bimetallic Sn-Ni-Beta catalyst was prepared which can convert glucose to methyl lactate (MLA) and methyl vinyl glycolate (MVG) in methanol at yields of 71.2 % and 10.2 %, respectively. Results from solid-state magic-angle spinning nuclear magnetic resonance, X-ray photoelectron spectroscopy, transmission electron microscopy, spectroscopic analysis, probe-temperature-programmed desorption, and density functional theory calculations conclusively reveal that the openness of the Sn sites, such as by the formation of [(SiO)₃−Sn−OH] entities, is governed by an adjacent metal cation such as Ni²⁺, Co²⁺, and Mn²⁺. This relies on the low structure-defective pore channel, provided by the current synthesis scheme, and the specific silica hydroxyl anchor point is associated with the incorporation of Sn for additional and precise metal ion localization. The presence of metal cations significantly improved the catalytic performance of Sn-Ni-Beta for glucose isomerization and conversion to MLA of sugar compared with Sn-Beta.     

Visualizing Chiral Interactions in Carbohydrates Adsorbed on Au(111) by High-Resolution STM Imaging

Carbohydrates are the most abundant organic material on Earth and the structural “material of choice” in many living systems. Nevertheless, design and engineering of synthetic carbohydrate materials presently lag behind that for protein and nucleic acids. Bottom-up engineering of carbohydrate materials demands an atomic-level understanding of their molecular structures and interactions in condensed phases. Here, high-resolution scanning tunneling microscopy (STM) is used to visualize at submolecular resolution the three-dimensional structure of cellulose oligomers assembled on Au(1111) and the interactions that drive their assembly. The STM imaging, supported by ab initio calculations, reveals the orientation of all glycosidic bonds and pyranose rings in the oligomers, as well as details of intermolecular interactions between the oligomers. By comparing the assembly of D- and L-oligomers, these interactions are shown to be enantioselective, capable of driving spontaneous enantioseparation of cellulose chains from its unnatural enantiomer and promoting the formation of engineered carbohydrate assemblies in the condensed phases.