Palladium catalysis enables cross-coupling-like SN2-glycosylation of phenols.

Despite their importance in life and material sciences, the efficient construction of stereo-defined glycosides remains a challenge. Studies of carbohydrate functions would be advanced if glycosylation methods were as reliable and modular as palladium (Pd)-catalyzed cross-coupling. However, Pd-catalysis excels in forming sp2-hybridized carbon centers whereas glycosylation mostly builds sp3-hybridized C-O linkages. We report a glycosylation platform through Pd-catalyzed SN2 displacement from phenols toward bench-stable, aryl-iodide-containing glycosyl sulfides. The key Pd(II) oxidative addition intermediate diverges from an arylating agent (Csp2 electrophile) to a glycosylating agent (Csp3 electrophile). This method inherits many merits of cross-coupling reactions, including operational simplicity and functional group tolerance. It preserves the SN2 mechanism for various substrates and is amenable to late-stage glycosylation of commercial drugs and natural products.

Nonenzymatic Stereoselective S-Glycosylation of Polypeptides and Proteins.

Here we report a nonenzymatic glycosylation reaction that builds axial S-glycosidic bonds under biorelevant conditions. This strategy is enabled by the design and use of allyl glycosyl sulfones as precursors to glycosyl radicals and exploits the exceptional functional group tolerance of radical processes. Our method introduces a variety of unprotected glycosyl units to the cysteine residues of peptides in a highly selective fashion. Through developing the second-generation protocol, we applied our method in the direct glycosylation of complex polypeptides and proteins. Computational studies were performed to elucidate the reaction mechanism.

A Radical Approach to Making Unnatural Amino Acids: Conversion of C-S Bonds in Cysteine Derivatives into C-C Bonds.

Here we report a general approach to make unnatural amino acids from readily available cysteine derivatives. This method capitalizes on an intramolecular radical substitution process that generates alkyl radicals through C-S cleavage. The resulting alkyl radicals partook in diverse C-C bond forming events. These reactions proceed under mild, photocatalytic conditions at room temperature, and can be performed open to air. The utility of these transformations is further demonstrated in the straightforward synthesis of various unnatural amino acids and peptides that are difficult to access previously.

[Migration Characteristics of Manganese During Rainfall Events and Its Impacts on Water Quality in a Drinking Water Source Reservoir].

In view of the problem of excessive manganese concentrations in the Xi'an Jinpen Reservoir during the flood season in 2017, the vertical distribution of manganese in density currents and its occurrence pattern were monitored at multiple monitoring sections along the upstream reaches to the main basin. The influences of density currents plunging into the reservoir on the migration and transformation of Mn were studied, and sedimentation, output, and deposition of manganese in the reservoir water were also specifically estimated during a single, typical storm runoff process. Devices for avoiding high turbidity and high load inflows in rainfall events were proposed. The results showed that significant increases of total manganese were induced by high-turbidity inflows, which largely degraded water quality during rainfall events. From 12 to 14 October, 9.11 tons of total manganese were transported into the reservoir during a single rainfall event, and the pollution conditions were largely remitted by flood discharges with an output of 6.22 tons; thus, the net deposition (manganese) was 1.47 tons. The manganese content and morphological changes along the upper reaches of the reservoir indicated that soil erosion occurred during the continuous rainfall process, and this caused a large amount of particulate pollutants to flow into the water body with the runoff. More than 70% of the total manganese in the water was in the iron-manganese oxide bound state. Correlation analysis was conducted with particles of different particle size ranges, and granular manganese particle sizes were about 2-20 µm. The findings indicate that when flood discharges with turbidity currents occur, this can effectively reduce the load of pollutants and the safety risks of water.

[Sources and Distribution of Phosphorus in Sediments of the Jinpen Reservoir].

In order to explore the sources and distribution of phosphorus in sediments of a stratified water source reservoir, the total phosphorus (TP) content and distribution of phosphorus fractions in sedimentation particles and sediments of the Jinpen Reservoir of Xi'an were analyzed from March to November in 2017. The results showed that the TP content in the surface sediments of the Jinpen Reservoir was obviously affected by the deposition of particulate phosphorus (PP), and the correlation coefficient was 0.8775. Besides, this TP pool was also affected by the biogeochemistry of sediments. From June to August, algae in the Jinpen Reservoir propagated intensely, and a large number of dead algae were deposited on the bottom of the water body, which resulted in a type of endogenous pollution dominated by algae. The concentration of PP reached (753.51±17.11) mg·kg-1, and the content of TP increased, with NaOH-nrP as the main component. During the flood season of the Jinpen Reservoir from September to November, the runoff water carried a large amount of sediments with large pollutant loads, which resulted in increases of the concentration of PP in the water body. However, the TP content in the sediment per unit mass was relatively small. As a result, the TP content of surface sediments decreased, with inorganic Ca-P and rest-P as the main forms, which accounted for 55.8%-66.2% of the TP in sediment, and were influenced by particle sedimentation. The SRP, BD-P, and NaOH-srP, the most active fractions, underwent a series of transport and transformation processes under the changing environmental conditions (mainly redox conditions), and these forms were obviously affected by the biochemical processes in sediments and minimally affected by the sedimentation processes of the reservoir.

Catalytic Asymmetric Synthesis of α-Tetrasubstituted α-Trifluoromethyl Homoallylic Amines by Ir-Catalyzed Umpolung Allylation of Imines.

A general and mild method to prepare enantioenriched α-trifluoromethyl, α-stereogenic homoallylic amines is established. This reaction, which involves an Ir-catalyzed umpolung allylation of imines and a 2-aza-Cope rearrangement cascade, could yield both tetrasubstituted and trisubstituted stereocenters. This transformation employs readily available starting materials and displays broad substrate scope. The isolation and structural determination of reaction intermediates revealed factors critical for the efficiency and stereoselectivity of this transformation.

Ni-Catalyzed Suzuki-Miyaura Cross-Coupling of α-Oxo-vinylsulfones To Prepare C-Aryl Glycals and Acyclic Vinyl Ethers.

We demonstrate that readily available and bench-stable α-oxo-vinylsulfones are competent electrophiles in Ni-catalyzed Suzuki-Miyaura cross-coupling reactions. The C-sulfone bond in the α-oxo-vinylsulfone motif is cleaved chemoselectively in these reactions, furnishing C-aryl glycals or acyclic vinyl ethers in high yields. These reactions proceed under mild conditions and tolerate a remarkable scope of heterocycles and functional groups. Preliminary mechanistic studies revealed the importance of an α-heteroatom in facilitating these transformations.