3-Exomethylene Sialic Acid Disaccharides as Substrate-Type Mechanism-Based Sialidase Inhibitors

We designed α(2,3)- and α(2,6)-sialylgalactose analogues bearing an exomethylene unit at C3 of sialic acid (3-exoSia) as a novel type of mechanism-based inhibitors of sialidases. Regio- and stereo-selective substitution by vinylogous activation enabled simultaneous construction of the 3-exomethylene moiety and the O-sialoside linkage. Both types of 3-exoSia disaccharides potently inhibit Clostridium perfringens sialidase NanI and selectively inhibit NEU2 among human sialidases, whereas the corresponding monosaccharide analogue is inactive. These analogues initially work as competitive inhibitors, but are gradually cleaved as substrates to generate a reactive species that forms a covalent bond with sialidase

Thienyl-Substituted α‑Ketoamide: A Less Hydrophobic Reactive Group for Photo-Affinity Labeling

Photoaffinity labeling (PAL) is an important tool in chemical biology research, but application of α-ketoamides for PAL has been hampered by their photoinstability. Here, we show that 2-thienyl-substituted α-ketoamide is a superior photoreactive group for PAL. Studies with a series of synthetic mannose-conjugated α-ketoamides revealed that 2-thienyl substitution of α-ketoamide decreased the electrophilicity of the keto group and reduced the rate of photodegradation. Mannose-conjugated thienyl α-ketoamide showed greater concanavalin A labeling efficiency than other alkyl or phenyl-substituted α-ketoamides. In comparison with representative conventional photoreactive groups, 2-thienyl ketoamide showed reduced labeling of nontarget proteins, probably owing to its lower hydrophobicity

Contribution of Cage-Shaped Structure of Physalins to Their Mode of Action in Inhibition of NF-κB Activation

A library of oxygenated natural steroids, including physalins, withanolides, and perulactones, coupled with the synthetic cage-shaped right-side structure of type B physalins, was constructed. SAR studies for inhibition of NF-κB activation showed the importance of both the B-ring and the oxygenated right-side partial structure. The 5β,6β-epoxy derivatives of both physalins and withanolides showed similar profiles of inhibition of NF-κB activation and appeared to act on NF-κB signaling via inhibition of phosphorylation and degradation of IκBα. In contrast, type B physalins with C5–C6 olefin functionality inhibited nuclear translocation and DNA binding of RelA/p50 protein dimer, which lie downstream of IκBα degradation, although withanolides having the same AB-ring functionality did not. These results indicated that the right-side partial structure of these steroids influences their mode of action