 The oxazolidinone pharmacophore — the chemical "template" essential for antimicrobial activity — consists of a 1,3-oxazolidin-2-one moiety with an aryl group at position 3 and an S-methyl group, with another substituent attached to it, at position 5 (the R-enantiomers of all oxazolidinones are devoid of antibiotic properties). In addition to this essential core, linezolid also contains several structural characteristics that improve its effectiveness and safety. An acetamide substituent on the 5-methyl group is the best choice in terms of antibacterial efficacy, and is used in all of the more active oxazolidinones developed thus far; in fact, straying too far from an acetamide group at this position makes the drug lose its antimicrobial power, although weak to moderate activity is maintained when some isosteric groups are used. A fluorine atom at the 3 ′ position practically doubles in vitro and in vivo activity, and the electron-donating nitrogen atom in the morpholine ring helps maintain high antibiotic potency and an acceptable safety profile.
