Preston Matzen (jaguarsecure51)

l-Rhamnose forms the key components of important antigenic oligo- and polysaccharides of a variety of pathogens. Obtaining 1,2-cis stereoselectivity in the glycosylation of l-rhamnoside is quite challenging due to the unavailability of neighboring group participation and disfavoring of the anomeric effect and stereoelectronic effect of the substituents on the C-2 axial position. Nevertheless, various methodologies have been developed exploiting diverse pathways for obtaining β-stereoselectivity in the glycosylation of l-rhamnose. This review describes the recent advances in β-l-rhamnosylation and its applications in the total synthesis of β-l-rhamnose-containing biologically important oligosaccharides.The selectivity of halogenation versus hydroxylation in α-KG de-pendent halogenases is vital to their function and has been widely studied, particularly using the halogenase SyrB2 as a model. WelO5, a new member of α-KG dependent halogenases, catalyzes the chlorination of 12-epi-fischerindole U in the welwitindolinone biosynthetic pathway. Herein, we give a detailed insight into the selectivity of WelO5 through combined quantum mechanical/molecular mechanical (QM/MM) calculations for the whole catalytic cycle. O2 activation leads to a Fe(iv)[double bond, length as m-dash]O moiety which adopts an equatorial conformation (in the plane consisting of His164, chloride and Fe atom), in contrast to axial conformation (perpendicular to the plane). Key to the conformational selectivity is a serine residue (Ser189) in the equatorial plane, that brings the precursor of the Fe(iv)[double bond, length as m-dash]O intermediate (a Fe(ii)-peracid complex) to the equatorial conformation through hydrogen bonding. Hydrogen abstraction of the substrate by the equatorial Fe(iv)[double bond, length as m-dash]O leads to a five-coordinated HO-Fe(iii)-Cl complex, where the hydroxyl ligand is still equatorial and thus relatively far from the substrate radical in the axial direction compared to the chloride ligand. This smoothly explains the extremely high selectivity of chlorination in WelO5 and provides a microscopic explanation for the experimental finding that S189A WelO5 ceases to display any chlorination selectivity versus hydroxylation. Notably, although Ser189 is vital for the selectivity of the enzyme, it is not part of the substrate binding pocket. Therefore, WelO5 serves as an excellent example how chemoselectivity can be achieved in directed evolution without the tedious redesign of the substrate binding pocket.Articular cartilage has limited self-healing ability due to its lack of abundant nutrients and progenitor cells. In this study, an injectable hydrogel system consisting of collagen type I-tyramine (Col-TA) and hyaluronic acid-tyramine (HA-TA) was fabricated as the bone marrow mesenchymal stem cell (BMSC)-laden hydrogel system for cartilage regeneration. Next, the physiochemical properties of this hydrogel system were well characterized and optimized, including gelation time, stiffness, water absorption and degradability. Further, the proliferation and differentiation of BMSCs within the Col-HA hydrogel were evaluated, and the ability of in vivo cartilage repair was also examined in the presence of the transforming growth factor-β1 (TGF-β1). These results illustrate that this hydrogel can offer a great microenvironment for BMSC growth and cartilage differentiation both in vitro and in vivo, and the Col-HA hydrogel can serve as an ideal hydrogel for cartilage tissue regeneration.In many biological processes, such as wound healing, cell tissues undergo an epithelial-to-mesenchymal transition, which is a transition from a more rigid to a more fluid state. Here, we investigate the solid/fluid transition of cell tissues within the framework of the self-propelled Voronoi model, which accounts for the deformability of the cells, for their many-body interactions, and for their polarized motility. The transition is controlled by two parameters,