 The oxazolidinone pharmacophore — the chemical " template " essential for antimicrobial activity — consists of a 1 @,@ 3 @-@ <unk> @-@ 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 <unk> 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 . 
