Sialic acids are ubiquitous components of mammalian cell membranes and key regulators of cellular recognition events. Located at the non‐reducing termini of bioactive gangliosides, these essential building blocks are fused to the polysaccharide core via a characteristic α‐linkage, and rarely occur in the monomeric form. Effective chemical strategies to enable α‐sialylation are urgently required to construct well‐defined tools for glycomics. To complement existing chemoenzymatic strategies, an α‐selective process has been devised based on the site‐selective introduction of fluorine at C3 (more than 20 examples, up to 90 % yield). Predicated on localized particle charge inversion (C−Hδ+→C−Fδ−), fluorine insertion simultaneously augments the anomeric effect, enhances electrophilicity at C2 and mitigates elimination. A stereochemical induction model is postulated that spans the SN continuum and validates the role of the C−F bond in orchestrating α‐selectivity.
The first total synthesis of carthamin (3), ah istoric natural red pigment, has been achieved. The molecular structure was efficiently constructed by assembling two equivalents of the in situ generated lithiated monomers and triisopropyl orthoformate.T his synthesis confirms the structure proposed in 1996.Carthamin is at raditional red pigment obtained from the petals of safflower, Carthamus tinctorius L. Thel ively petals appear mostly yellow (Figure 1a), [1a] reflecting ap revalence Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.
Double-four ring (D4R)-type cage germanoxanes, having fluoride anion in the cage, contain organic ammonium cations as counter cations outside the cage, and they are attractive as unique nano-building blocks of...
What is the most significant result of this study?We have demonstrated that functionalization of the corners of cage germanoxanes with silyl groups was successful by using a combination of chlorosilane and silazane to minimize the generation of hydrogen chloride. This finding opens the door for applications of the cage germanoxane in various fields. In this study,w e have established an effective method for the functionalization of a cubic cage germanoxane containing af luoride ion inside the cage. The cage germanoxane is expected to show various unique properties owing to its charge and rigid structure. For the molecular design of cage germanoxane as versatile building blocks, the introduction of organic functional groups onto the corner Ge atoms is essential.What was the inspiration for this cover design?We represented ac age germanoxane as ab irdcage and af luoride ion as ab ird caught in the cage. Silyl groups are represented as yellow birds catching the birdcage and flying up to the sky,w hich expresses successful silylation of the cage germanoxane and a bright future for cage germanoxane.What was the biggest surprise (on the way to the results presented in this paper)?When we started this study,w ea ssumed that silylation of germanoxane could proceed without any problem. However,t he cage was decomposed when chlorosilane was used as as ilylating agent, and the reaction did not proceed when silazane was used. Successful silylation using ac ombination of chlorosilane and silazane surprised us and gave atremendous boost to our research.Invited for the cover of this issue is the group of Atsushi Shimojima and Kazuyuki Kuroda at Waseda University.T he image depicts the functionalization of ac ubic cage germanoxane( birdcage) containing af luoridei on (blueb ird) inside the cage. Read the full text of the article at
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