Patent ID: 7132541

Claim:
A method for enhancing optical purity of S-(−)-9-fluoro-6,7-dihydro-8-(4-hydroxypiperidin-1-yl)-5-methyl-1-oxo-1H,5H-benzo[i,j]quinolizine-2-carboxylic acid L-arginine salt comprising, the steps of: (a) suspending a partially optically impure mixture of 9-fluoro-6,7-dihydro-8-(4-hydroxypiperidin-1-yl)-5-methyl-1-oxo-1H,5H-benzo[i,j]quinolizine-2-carboxylic acid in water and organic solvent selected from acetone or acetonitrile to form a suspension, (b) adding an equimolar quantity of L-arginine to the suspension and heating the suspension to a temperature between about 40 to 70° C. to obtain a clear solution, (c) adding 2 to 3 times more of the organic solvent added in step (a), (d) cooling the solution to 0 to 45° C., for 1 hr to 5 hr, to effect the crystallization; (e) isolating the crystalline form of S-(−)-9-fluoro-6,7-dihydro-8-(4-hydroxypiperidin-1-yl)-5-methyl-1-oxo-1H,5 H-benzo[i,j]quinolizine-2-carboxylic acid L-arginine salt at below 35° C. by filtration, and (f) drying the crystalline form of S-(−)-9-fluoro-6,7-dihydro-8-(4-hydroxypiperidin-1-yl)-5-methyl-1-oxo-1H,5H-benzo[i,j]quinolizine-2-carboxylic acid L-arginine salt.