Simple and Efficient Synthesis of 3-Aryl-2-oxazolidinone Scaffolds Enabling Increased Potency toward Biofilms

Abstract

Infectious diseases caused by bacterial pathogens are a leading cause of mortality worldwide. In particular, recalcitrant bacterial communities known as biofilms are implicated in persistent and difficult to treat infections. With a diminishing antibiotic pipeline, new treatments are urgently required to combat biofilm infections. An emerging strategy to develop new treatments is the hybridization of antibiotics. The benefit of this approach is the extension of the useful lifetime of existing antibiotics. The oxazolidinones, which include the last resort antibiotic linezolid, are an attractive target for improving antibiofilm efficacy as they present one of the most recently discovered classes of antibiotics. A key step in the synthesis of new 3-aryl-2-oxazolidinone derivatives is the challenging formation of the oxazolidinone ring. Herein we report a direct synthetic route to the piperazinyl functionalized 3-aryl-2-oxazolidinone 17. We also demonstrate an application of these piperazine molecules by functionalizing them with a nitroxide moiety as a strategy to extend the useful lifetime of oxazolidinones and improve their potency against Methicillin-resistant Staphylococcus aureus (MRSA) biofilms. The antimicrobial susceptibility of the linezolid-nitroxide conjugate 11 and its corresponding methoxyamine derivative 12 (a control for biofilm dispersal) was assessed against planktonic cells and biofilms of MRSA. In comparison to linezolid and our lead compound 10 (a piperazinyl oxazolidinone derivative), the linezolid-nitroxide conjugate 11 displayed a minimum inhibitory concentration that was 4–16-fold higher. The opposite effect was seen in biofilms where the linezolid-nitroxide hybrid 11 was >2-fold more effective (160 μg/mL versus >320 μg/mL) in eradicating MRSA biofilms. The methoxyamine derivative 12 performed on par with linezolid. The drug-likeness of the compounds was also assessed, and all compounds were predicted to have good oral bioavailability. Our piperazinyl oxazolidinone derivative 10 was confirmed to be lead-like and would be a good lead candidate for future functionalized oxazolidinones. The modification of antibiotics with a dispersal agent appears to be a promising approach for eradicating MRSA biofilms and overcoming the antibiotic resistance associated with the biofilm mode of growth.

In Vitro Activities of Oxazolidinone Antibiotics Alone and in Combination with C-TEMPO against Methicillin-Resistant Staphylococcus aureus Biofilms

“…In comparison to linezolid, the structure of ranbezolid replaces the morpholine moiety with a piperazine ring attached to a nitrofuran via a methylene linker. Our previous work showed the piperazinyl oxazolidinone derivative is not able to eradicate S. aureus biofilms completely [59]. Therefore, it is suspected that the key to ranbezolid's potent antibiofilm activity lies in its nitrofuran ring.…”

“…We hypothesize that ranbezolid functions as a 'dual-warhead' drug to eradicate biofilms and acts via the oxazolidinone mode of action and as either a nitric oxide donor or cytotoxic drug because of its nitrofuran ring (Figure 4). While the exact mechanism of action of nitroxide hybrid drugs is currently unknown [59,60,87], nitroxides are considered to be nitric oxide mimics. Combination treatment was then used to explore whether the susceptibility of ranbezolid and linezolid could be enhanced with the nitroxide C-TEMPO.…”

“…Previous studies have established that nitroxides can induce the dispersal of biofilms [59,60] We sought to investigate whether the nitroxide C-TEMPO could synergistically increase the susceptibility of MRSA biofilms to oxazolidinone antibiotics. As ranbezolid had the lowest MBEC value, and linezolid, tedizolid, deacetyl linezolid thioacetamide and radezolid performed similarly against MRSA biofilms, linezolid and ranbezolid were chosen as the representative antibiotics in this experiment.…”

Synthesis and Biological Activities of Oxazolidinone Pleuromutilin Derivatives as a Potent Anti-MRSA Agent

“…Molecular docking experimental method: delete Tiamulin and water molecules on 1XBP, hydrogenate and assign Gasteiger charges, prepare receptor molecules and ligand molecules by AutoDockTools, set the box with the initial ligand Tiamulin as the center of the box (center_x = 52.564, center_y = 123.356, center_z = 114.265), box size (20,20,20). AutoDock Vina 36 was employed for molecular docking and the docking results were analyzed using Pymol.…”

“…Modification of the pleuromutilin parent ring is difficult, and the antibacterial activity does not improve significantly. , Some studies have suggested that all pleuromutilin derivatives have a similar binding mode in the tricyclic mutilin core when combined with PTC, while the C-14 side chain varies considerably in the binding position. , In particular, the incorporation of five-membered heterocycles, such as triazole and oxadiazole, into the side chain of pleuromutilin enhances its antibacterial performance. Oxazolidinone is a bioactive fragment that has been introduced as an active functional group in the development of antibacterial drugs with good results. − For example, linezolid, tedizolid, and contezolid have been successively approved, which has greatly increased our interest in introducing these active structures. Furthermore, oxazolidinone has the advantage of containing multiple heteroatoms, which allows it to bind to surrounding receptor residues and improve water solubility.…”