Patent ID: 7629458

Claim:
A method for preparing (S)-(−)-9-fluoro-2,3-dihydro-3-methyl-10-(4-methyl-1-piperazinyl)-7-oxo-7H-pyrido[1,2,3-de]-1,4-benzoxazine-6-carboxylic acid hemihydrate, comprising: maintaining levofloxacin at a first elevated temperature in a first solvent, wherein the first solvent is a polar solvent capable of dissolving levofloxacin, wherein the polar solvent capable of dissolving levofloxacin is selected from the group consisting of dimethylsulfoxide (DMSO), isobutanol, n-BuOH, ketone, propylene-glycol-monomethyl-ether (PGME) and dimethyl acetamide (DMA); adding water or a polar solvent comprising water to precipitate levofloxacin, wherein the polar solvent is selected from the group consisting of isopropyl alcohol (IPA), IPA/H 2 O, BuOH, acetonitrile (ACN), methyl ethyl ketone (MEK), and DMSO/H 2 O; and recovering the (S)-(−)9,10-difluoro-3-methyl-7-oxo-2,3-dihydro-7H-pyrido[1,2,3-de][1,4]benzoxazine-6-carboxylic acid hemihydrate.