113028-17-4

112984-60-8

The general procedure for the synthesis of 6-fluoro-1-methyl-4-oxo-7-(piperazin-1-yl)-1,4-dihydro-[1,3]thiazolo[3,2-a]quinoline-3-carboxylic acid from ethyl 6-fluoro-1-methyl-4-oxo-7-(1-piperazinyl)-1,4-dihydro-[1,3]thiazolo[3,2-a]quinoline-3-carboxylate was as follows: 1. ethyl 6-fluoro-1-methyl-4-oxo-7-(1-piperazinyl)-4H-[1,3]thiazolo[3,2-a]quinoline-3-carboxylate (100 g, 0.265 mol) was dissolved in water (600 ml) at 25-30 °C with stirring. 2. potassium hydroxide solution (50 g of potassium hydroxide flakes dissolved in 200 ml of water) was slowly added to this solution. 3. the reaction mixture is heated to 80-85°C and stirred at this temperature for 1 hour. 4. After completion of the reaction, the reaction mixture was cooled down to 25-30 °C. The reaction mixture was then cooled down to 25-30 °C. 5. The pH of the reaction mixture was adjusted to 6.5-7.0 using a 1:1 aqueous solution of acetic acid. 6. The reaction mixture was stirred at room temperature for 1 hour to allow the product to fully precipitate. 7. The precipitated solid was collected by filtration and washed with distilled water (2 x 100 mL). 8. The solid was slurried in methanol (300 ml) at 25-30 °C for 1 h. The reaction mixture was stirred for 1 h at room temperature. 9. After filtration, the solid was washed with methanol (2 x 50 ml). 10. The product was dried under vacuum at 70-75 °C to afford 6-fluoro-1-methyl-4-oxo-7-(piperazin-1-yl)-1,4-dihydro-[1,3]thiazeto[3,2-a]quinoline-3-carboxylic acid (90 g, 97% yield, 96% HPLC purity).