Oxazolidinone

Discovery

The first antimicrobial oxazolidinones were identified at the DuPont company in 1978 and reported in their patent literature (Shaw and Barbachyn, 2011). Testing a series of this class of molecules found them to be unsafe for clinical use. More than 30 companies worked on developing leads for the clinical advancement of oxazolidinones. By the early 1990s another company, Upjohn, had developed several analogs, one of which, linezolid, showed promise as a therapeutic agent for human use. It inhibits functional 70S initiation complex formation and does not cross-react with existing bacterial resistance. The oral bioavailability of this antibiotic in humans was high (100%), and they were effective against significant gram-positive pathogens (Ford et al., 2001).

Overview of Chemistry

The hallmark of this class of molecules is the 2-oxazolidone ring (marked with an oval dashed line in Figure 1A). Linezolid, the first clinically relevant molecule in this class, consists of four main parts: three rings (A-C) and one acetamidomethyl (C5 tail), where ring-A is the oxazolidinone ring.

Oxazolidinones function by preventing the assembly of the ribosome by binding to the 50s ribosomal subunit. In the case of linezolid, the oxazolidone ring and C5 tail bind to the 50s ribosomal subunit and point toward the tunnel. Ring A stacks on a specific base (U2504) of the 23s rRNA (Wilson et al., 2008). Ring-C orients itself towards the inter-subunit interface. Learn more about linezolid binding to the ribosome.

Figure 1: 2D drawings of oxazolidinones. A. Linezolid (CC ID ZLD); B. Tedizolid (CC ID U7V); and C. Contezolid (CC ID ZC0). The main functional group is highlighted with ovals in dashed lines.

Types

Linezolid is the most studied antibiotic in this class. However, other molecules have also been developed. By keeping the 2-oxazolidone intact, and adding different substitutions around it (e.g., linked to the N atom in the ring) other oxazolidinone molecules were designed. For example, the molecule tedizolid (CC ID U7V, Figure 1B) is another antibiotic approved by the US FDA for the treatment of certain gram-positive bacterial infections (Wright et al., 2020), while Contezolid (or MRX-I, CC ID ZC0, Figure 1C) and radezolid (not shown in figure) are still undergoing clinical trials (at the time of this writing).

Resistance

Compared to other antimicrobial agents, reports of spontaneous resistance for oxazolidinones are relatively rare. Mutations in the 23s rRNA and specific positions in the ribosomal proteins L3 and L4 may lead to resistance (Shaw and Barbachyn, 2011). Another mechanism of resistance is the cfr gene, which may be transferred via a range of plasmids, transposons, and insertion elements, originally identified in veterinary (cattle, swine) staphylococcal isolates (Schwarz et al., 2000). Learn more about linezolid resistance.

References

Ford, C. W., Zurenko, G. E., Barbachyn, M. R. (2001) The discovery of linezolid, the first oxazolidinone antibacterial agent. Curr Drug Targets Infect Disord. 1(2):181-99. https://doi.org/10.2174/1568005014606099

Schwarz, S., Werckenthin, C., Kehrenberg, C. (2000) Identification of a plasmid-borne chloramphenicol-florfenicol resistance gene in Staphylococcus sciuri. Antimicrob Agents Chemother. 44(9):2530-3. https://doi.org/10.1128/aac.44.9.2530-2533.2000

Shaw, K. J., Barbachyn, M. R. (2011) The oxazolidinones: past, present, and future. Ann N Y Acad Sci. 1241:48-70. https://doi.org/10.1111/j.1749-6632.2011.06330.x

Wilson, D.N., Schluenzen, F., Harms, M.J., Starosta, A.L., Connell, S.R, Fucini, P. (2008). The oxazolidinone antibiotics perturb the ribosomal peptidyl-transferase center and effect tRNA positioning. Proceedings of the National Academy of Sciences of the United States of America, 105(36) 13339-13344. https://doi.org/10.1073/pnas.0804276105

Wright, A., Deane-Alder, K., Marschall, E., Bamert, R., Venugopal, H., Lithgow, T., Lupton, D. W., Belousoff, M. J. (2020) Characterization of the Core Ribosomal Binding Region for the Oxazolidone Family of Antibiotics Using Cryo-EM. ACS Pharmacol Transl Sci. 3(3):425-432. https://doi.org/10.1021/acsptsci.0c00041