Fluoro-Carba-Sugars are Glycomimetic Activators of the glmS Ribozyme.

The glmS ribozyme is a bacterial gene-regulating riboswitch that controls cell wall synthesis, depending on glucosamine-6-phosphate as a cofactor. Due to the presence of this ribozyme in several human pathogen bacteria (e.g., MRSA, VRSA), the glmS ribozyme represents an attractive target for the development of artificial cofactors. The substitution of the ring oxygen in carbohydrates by functionalized methylene groups leads to a new generation of glycomimetics that exploits distinct interaction possibilities with their target structure in biological systems. Herein, we describe the synthesis of mono-fluoro-modified carba variants of α-d-glucosamine and ß-l-idosamine. (5aR)-Fluoro-carba-α-d-glucosamine-6-phosphate is a synthetic mimic of the natural ligand of the glmS ribozyme and is capable of effectively addressing its unique self-cleavage mechanism. However, in contrast to what was expected, the activity is significantly decreased compared to its non-fluorinated analog. By combining self-cleavage assays with the Bacillus subtilis and Staphylococcus aureus glmS ribozyme and molecular docking studies, we provide a structure-activity relationship for fluorinated carba-sugars.

Activation of the glmS Ribozyme Confers Bacterial Growth Inhibition.

The ever-growing number of pathogenic bacteria resistant to treatment with antibiotics call for the development of novel compounds with as-yet unexplored modes of action. Here, we demonstrate the in vivo antibacterial activity of carba-α-d-glucosamine (CGlcN). In this mode of action study, we provide evidence that CGlcN-mediated growth inhibition is due to glmS ribozyme activation, and we demonstrate that CGlcN hijacks an endogenous activation pathway, hence utilizing a prodrug mechanism. This is the first report describing antibacterial activity mediated by activating the self-cleaving properties of a ribozyme. Our results open the path towards a compound class with an entirely novel and distinct molecular mechanism.

The promise of riboswitches as potential antibacterial drug targets.

Riboswitches represent promising novel RNA structures for developing compounds that artificially regulate gene expression and, thus, bacterial growth. The past years have seen increasing efforts to identify metabolite-analogues which act on riboswitches and which reveal antibacterial activity. Here, we summarize the current inventory of riboswitch-targeting compounds, their characteristics and antibacterial potential.