Regio- and Stereoselective Organocatalyzed Relay Glycosylations To Synthesize 2-Amino-2-deoxy-1,3-dithioglycosides.

Herein, we describe a novel methodology for the regio- and stereoselective convergent synthesis of 2-amino-2-deoxy-dithioglycosides via one-pot relay glycosylation of 3-O-acetyl-2-nitroglucal donors. This unique organo-catalysis relay glycosylation features excellent site- and stereoselectivity, good to excellent yields, mild reaction conditions, and broad substrate scope. 2-Amino-2-deoxy-glucosides/mannosides bearing 1,3-dithio-linkages were efficiently obtained from 3-O-acetyl-2-nitroglucal donors in both stepwise and one-pot glycosylation protocols. The dithiolated O-antigen of E. coli serogroup 64 was successfully synthesized using this newly developed method.

Hydrogen bond activated glycosylation under mild conditions.

Herein, we report a new glycosylation system for the highly efficient and stereoselective formation of glycosidic bonds using glycosyl N-phenyl trifluoroacetimidate (PTFAI) donors and a charged thiourea hydrogen-bond-donor catalyst. The glycosylation protocol features broad substrate scope, controllable stereoselectivity, good to excellent yields and exceptionally mild catalysis conditions. Benefitting from the mild reaction conditions, this new hydrogen bond-mediated glycosylation system in combination with a hydrogen bond-mediated aglycon delivery system provides a reliable method for the synthesis of challenging phenolic glycosides. In addition, a chemoselective glycosylation procedure was developed using different imidate donors (trichloroacetimidates, N-phenyl trifluoroacetimidates, N-4-nitrophenyl trifluoroacetimidates, benzoxazolyl imidates and 6-nitro-benzothiazolyl imidates) and it was applied for a trisaccharide synthesis through a novel one-pot single catalyst strategy.

Source identification and comprehensive apportionment of the accumulation of soil heavy metals by integrating pollution landscapes, pathways, and receptors.

Existing source apportionment methods for soil heavy metals fail to identify the actual landscapes related to pollutant sources and quantify their contributions to the accumulation of soil heavy metals. In this work, we propose a new source identification and apportionment approach for soil heavy metal accumulation by integrating pollution landscapes, pathways, and receptors. Datasets for soil lead (Pb) concentrations in Daye city, China, which was sampled in 2018, were used. First, based on the spatial distribution of Pb, the source landscapes were identified using GeoDetector and spatial analysis methods. Second, a source landscape apportionment model (SLAM) was developed considering both atmospheric deposition and surface runoff as diffusion pathways. Third, considering soil properties and topography as receptor attributes, ordinary least squares (OLS) and geographically weighted regression (GWR) models were employed to further adjust the soil Pb accumulation at receptor locations. The results showed that SLAM followed by the GWR model (SLAM-GWR) had the highest fitting accuracy. Then, the spatial distributions and ranges of contributions of each identified source landscape to Pb accumulation through different pathways were obtained. Finally, the advantages and disadvantages of the proposed approach were discussed.