The title compound is prepared by reductive alkylation of the known piperazinyl oxazolidinone derivative (I) with 5-nitro-2-furfural (II) in the presence of NaBH(OAc)3, followed by conversion to the corresponding hydrochloride salt.

The antibacterial activity of RBx-7644 is due to the 5(S)-acetamidomethyl configuration at the oxazolidinone ring, and thus, asymmetric synthesis of only the 5(S)-enantiomer was desirable: 3,4-Difluoronitrobenzene (I) is condensed with piperazine in acetonitrile to give 4-(2-fluoro-4-nitrophenyl)-piperazine (II) as a light yellow compound. Compound (II) is dissolved in dichloromethane and triethylamine, followed by the addition of Boc-anhydride, to provide compound (III). 4-(tert-Butoxycarbonyl)-1-(2-fluoro-4-nitrophenyl)piperazine (III), upon hydrogenation with H2 over Pd/C in methanol at 50 psi, yields 4-(tert-butoxycarbonyl)-1-(2-fluoro-4-aminophenyl)piperazine (IV) as a dark solid. Compound (IV) reacts with benzylchloroformate in dry THF in the presence of solid sodium bicarbonate to afford the desired compound (V). 4-(tert-Butoxycarbonyl)-1-[2-fluoro-4-(benzyloxycarbonylamino)phenyl]piperazine (V), upon treatment with n-BuLi and (R)-glycidyl butyrate at -78 癈, gives the desired (R)-(-)-3-[3-fluoro-4-[4-(tert-butoxycarbonyl)piperazin-1-yl]phenyl]-5-(hydroxymethyl)-2-oxazolidinone (VI). The hydroxymethyl compound (VI) is treated with methanesulfonyl chloride in dichloromethane in the presence of triethylamine to give (R)-(-)-3-[3-fluoro-4-[4-(tert-butoxycarbonyl)piperazin-1-yl]phenyl]-5-(methylsulfonyloxymethyl)-2-oxazolidinone (VII). The sulfonyl derivative (VII) is treated with sodium azide in dimethylformamide to provide the azide (VIII) as a white solid. (R)-(-)-3-[3-Fluoro-4-[4-(tert-butoxycarbonyl)piperazin-1-yl)phenyl]-5-(azidomethyl)-2-oxazolidinone (VIII), upon hydrogenation with H2 over Pd/C at 45 psi, gives (S)-(-)-3-[3-fluoro-4-[4-(tert-butoxycarbonyl)-piperazin-1-yl]phenyl]-5-(aminomethyl)-2-oxazolidinone (IX). The aminomethyl compound (IX), upon treatment with acetic anhydride in dichloromethane in the presence of triethylamine, affords the acetamide derivative (X). The acetamidomethyl-oxazolidinone derivative (X), upon treatment with trifluoroacetic acid, gives (S)-(-)-3-[3-fluoro-4-(1-piperazinyl)phenyl]-5-(acetamidomethyl)-2-oxazolidinone, which, without isolation, is treated with 5-nitro-2-furaldehyde in the presence of sodium triacetoxy borohydride to provide compound (XI). Compound (XI), upon treatment with ethanolic HCl, affords RBx-7644 as a light yellow crystalline solid.