Synthesis
Levofloxacin carboxylic acid was synthesized using ethyl (S)-9,10-difluoro-3-methyl-7-oxo-3,7-dihydro-2H-[1,4]oxazino[2,3,4-ij]quinoline-6-carboxylate as starting material in the following steps:
1. to the residue after recovery of DMF was added acetic acid followed by 65 mL of water at room temperature and mixed with stirring.
2. sulfuric acid was slowly added dropwise, and when the dropwise addition was complete, it was heated to reflux and kept at reflux for 1 hour.
3. upon completion of the reaction, cooled to room temperature and subjected to filtration.
4. The filter cake was washed with 65 mL of water and subsequently dried to give 43.98 g of levodicyclic acid, the content of which was determined to be 96.22%.
5. The acetic acid was spun back through acetic acid and spun to dryness.
6. The filtrate was washed with water and filtered again to give 4.81 g of levulinic acid at 61.28%.
7. The recycled water and acetic acid can be recycled separately to minimize waste discharge and reduce raw material costs.
8. For the synthesis of tetrafluorobenzoyl chloride, the total yield after four steps was 87%.
References
[1] Patent: EP368410, 1990, A3
[2] Chemical and pharmaceutical bulletin, 1987, vol. 35, # 5, p. 1896 - 1902
[3] Bioorganic and Medicinal Chemistry Letters, 2003, vol. 13, # 23, p. 4213 - 4216
[4] Patent: WO2006/48889, 2006, A1. Location in patent: Page/Page column 18
[5] Patent: US4985557, 1991, A
![Ethyl (S)-9,10-difluoro-3-methyl-7-oxo-2,3-dihydro-7H-pyrido[1,2,3-de]-1,4-benzoxazine-6-carboxylate](/CAS/GIF/106939-34-8.gif)
