Glycans are complex compounds consisting of sugars linked glycosidically, existing either as pure polysaccharides or as part of glycoconjugates. They are prevalent in nature and possess important functions in regulating biological pathways. However, their diversity coupled with physiochemical similarities makes it challenging to isolate them in large quantities for biochemical studies, hence hampering progress in glycobiology and glycomedicine. Glycochemistry presents an alternative strategy to obtain pure glycan compounds through artificial synthetic methods. Efforts in glycochemistry have been centered on glycosylation, the key reaction in glycochemistry, especially with regards to anomeric stereoselectivity in polysaccharides and glycoconjugates. In particular, the stereoelectronic and steric properties of glycosyl donors are commonly used to direct the stereoselectivity in glycosylation reactions. Classic glycosylation strategies typically involve saturated glycosyl donors, proceeding either directly using hydrogen bonds and conformational constraints or indirectly by installing moieties covalently through neighboring group participation and intramolecular aglycon delivery. Over the past years, new glycosylation strategies, tapping on the foundations of transition metal catalysis, have emerged. To leverage the power of coordination chemistry, unsaturated glycosyl donors were introduced. Not only are the number of protection/deprotection steps reduced, the resultant unsaturated glycoside provides opportunities for downstream functionalizations, allowing quick access to a variety of sugars, including rare sugars. Alongside the glycosyl donor, an equally important but neglected aspect for targeting stereoselective glycosylation is the glycosyl acceptor. In the case of dual-directing donors, glycosyl acceptors have proved themselves capable of becoming the dominating factor for stereocontrol. Interestingly, rational manipulation or selection of glycosyl acceptors with particular nucleophilicity and p K values can lead to different stereoselectivities, thereby proving the tunability of such acceptors to favor the formation of one anomer over the other stereoselectively. By further venturing beyond substrate controlled stereoselectivity, we are presented with the opportunity to effect stereoselective glycosylation through glycosylating reagents. Of the key reagents, stereoselective catalyst stands out as a greener and efficient alternative to direct stereoselective control with stoichiometric substrates. Recently, investigations into this approach of stereocontrol presented an intriguing range of stereoselectivities, achieved by merely varying the nature of catalysts used. Another crucial effort in glycochemistry is enhancing the efficiencies of glycosylations, by reducing the number of preparative steps before or during glycosylation. Through using transient masking groups or one-pot synthetic strategies, these streamlined approaches provide enormous convenience and practicability for oligosaccharide syntheses. Th...

Bacterial infection is becoming increasingly lethal with the emergence of antimicrobial resistance, and wounds plagued by such infection are notoriously difficult to heal. Here, the first use of galactose-black phosphorus nanosheets, (Gal-BP NSs) as a delivery platform for synergistic antibiotic (kanamycin, Kana) and photothermal treatments against the Gram-negative microbial strain, Pseudomonas aeruginosa PAO1 (PAO1) is reported. Gal-BP NSs@Kana can actively target PAO1 and release kanamycin into the bacterial cytoplasm upon near-infrared laser irradiation. This strategy kills most of the PAO1 through a simultaneous burst of intracellular kanamycin release and photothermal treatment. Comparable antibacterial activities of Gal-BP NSs@Kana are observed within in vivo mouse models at their wound sites. In addition, this platform accelerates wound healing from PAO1 infection via promotion of neoangiogenesis and collagen production at the wound sites. This work demonstrates the material properties of Gal-BP NS in fighting bacterial infections and in the treatment of wound healing.

Stereoselective construction of various O-glycosidic bonds was first achieved by different palladium sources using 3,4-O-carbonate galactal as the donor to reach yields up to 95% under mild conditions. With Pd­(II) catalyst coordination of this glycal donor from the β-face directed by carbonate group, hard nucleophiles (aliphatic alcohols) gave β-glycosides and α-glycosides were obtained from soft nucleophiles (phenols). In contrast, with the Pd(0) catalyst coordinating the donor from the β-face due to steric effect, both hard and soft acceptors could only generate β-glycosides via hydrogen-bond-mediated aglycone delivery.

An efficient and concise method for the construction of various O-glycosidic bonds by a palladium-catalyzed reaction with a 3-O-picoloyl glucal has been developed. The stereochemistry of the anomeric center derives from either an inner-sphere or outer-sphere pathway. Harder nucleophiles, such as aliphatic alcohols and sodium phenoxides give β-products, and α products result from using softer nucleophiles, such as phenol.

This review delivers insights for dedicated chemists into the development of efficient methods in accessing carbohydrates at a lower cost.