Synthesis
Descarboxyl Levofloxacin was prepared as follows:
Take 0.03 mol of levofloxacin (10.83 g) and place it in a pressure-resistant reaction flask equipped with a spherical condenser. Add 1000 ml of 1 mol/L hydrochloric acid solution and stir to dissolve at 60–80 °C. Heat at 120 °C and 0.3 MPa for 50 hours. Evaporate the solution to dryness in a 100 °C water bath while simultaneously allowing HCl to evaporate completely, yielding a residue of 9.45 g. Recrystallize the residue repeatedly using a mixed solvent of ethanol and acetone in a volume ratio of 2:1. The recrystallization includes the following steps:
(1) Crystallization: Add 100 times the weight of the mixed solvent to the residue, heat to 80°C, stir to dissolve the residue, filter, concentrate the filtrate to 2/3 volume, place in a 4°C refrigerator for 2 hours to precipitate crystals, filter, wash the crystals several times with the mixed solvent, combine the filtrate and washings, concentrate to 200 ml, place in a 4°C refrigerator for 2 hours to precipitate crystals, repeat the filtration, washing, and crystallization steps 3 times, combine the obtained crystals to obtain crude Descarboxyl Levofloxacin 1;
(2) Recrystallization: Take crude Descarboxyl Levofloxacin, add 150 times its weight of mixed solvent, heat to 60℃ and stir to dissolve the decarboxylated crude levofloxacin, filter, concentrate the filtrate to 2/5, place in a 4℃ refrigerator for 2 hours, crystals precipitate, filter, wash the crystals several times with mixed solvent, combine the filtrate and washings, concentrate to 200ml, place in a 4℃ refrigerator for 2 hours, crystals precipitate, repeat the filtration, washing and crystallization steps 3 times, combine the obtained crystals to obtain crude Descarboxyl Levofloxacin 2;
(3) Repeat step (2) 1-2 times, the obtained crystals are 8.3g, which is Descarboxyl Levofloxacin, with a yield of 87%.
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