The Diels-Alder reaction with inverse electron demand (DAinv reaction) of 1,2,4,5-tetrazines with electron rich or strained alkenes was proven to be a bioorthogonal ligation reaction that proceeds fast and with high yields. An important application of the DAinv reaction is metabolic oligosaccharide engineering (MOE) which allows the visualization of glycoconjugates in living cells. In this approach, a sugar derivative bearing a chemical reporter group is metabolically incorporated into cellular glycoconjugates and subsequently derivatized with a probe by means of a bioorthogonal ligation reaction. Here, we investigated a series of new mannosamine and glucosamine derivatives with carbamate-linked side chains of varying length terminated by alkene groups and their suitability for labeling cell-surface glycans. Kinetic investigations showed that the reactivity of the alkenes in DAinv reactions increases with growing chain length. When applied to MOE, one of the compounds, peracetylated N-butenyloxycarbonylmannosamine, was especially well suited for labeling cell-surface glycans. Obviously, the length of its side chain represents the optimal balance between incorporation efficiency and speed of the labeling reaction. Sialidase treatment of the cells before the bioorthogonal labeling reaction showed that this sugar derivative is attached to the glycans in form of the corresponding sialic acid derivative and not epimerized to another hexosamine derivative to a considerable extent.
The combined use of “biological” RNA imaging methods based on MS2 technology and “chemical” RNA detection by FIT probes allows unambiguous cellular imaging of a C → U edit in mRNA encoding for GlyR α2.
Invited for the cover of this issue are Valentin Wittmann and his co‐workers at the University of Konstanz. The image depicts their “sugar champion” and its labeling on cell membranes in a way one might enjoy during the soccer world cup. Read the full text of the article at .
Efficient fluorogenic hybridization probes combine high brightness and specificity of fluorescence signaling with large turn-on of fluorescence. Herein, we present an approach to enhance signaling by combining two identical fluorescence...
Chemically modified mannosamine derivatives with side chains of different length terminated by alkenes were applied for metabolic oligosaccharide engineering (MOE). During MOE, the sugars are transformed by cells into the corresponding sialic acids and incorporated into cell‐surface glycoconjugates. As terminal alkenes can function as dienophiles during inverse‐electron‐demand Diels–Alder reactions, the sugars can be fluorescently labeled by ligation to a tetrazine conjugate. The compound with a butenyloxycarbonyl side chain leads to the optimal balance between incorporation efficiency and speed of the ligation reaction, resulting in the most intense fluorescence signal. For more details, see the Full Paper by V. Wittmann et al. on
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