Ciprofloxacin.HCL needed to react with heat sensitive amino reactant. Reaction of Ciprofloxacin with thionyl was not successful in producing the acid chloride derivative of Ciprofloxacin.
Ghadeer
You may try this method
A solution of (1 mmol) of the acid (1 mmol) of HATU and 0.28 mL (2 mmol) of triethylamine (TEA) in 2 mL dimethylformamide (DMF) is stirred at 0o C for 3 min. Then the amine (1 mmol) is added. The reaction mixture is stirred at 0o C for 1 h and left overnight at room temperature. The reaction mixture is poured into ice water, filtered, washed with 5% aqueous citric acid solution (2 x 10 mL), saturated sodium bicarbonate solution (2 x 10 mL) and water.
--- Exploring new selective 3-Benzylquinoxaline-based MAO-A inhibitors: Design, Synthesis, biological evaluation and docking studies, S. Khattab, S. Amin, A.M. El Massry, A. Bekhit, A. El-Faham, and S. Yassin, A. El-Faham and H. Ahmed, Adel Amer Europ. J. Med. Chem. 93, 308-320 (2015).
Good luck
(1) After reaction with thionyl chloride instead of isolating acid chloride it may be treated with amine in situ.
(2) For the preparation of acid chloride PCl5 or PCl3 may also be Tried.
(3)Reaction may be Tried at low temperature say 0-5 degree C .
You will probably need to protect the free amine group first. boc is your best choice here, i think...
Have you considered CDI (carbonyldiimidazole)? Or try propylphosphonic anhydride as a more gentle activating agent. Its side products might also be more readily washed out compared to more conventional peptide coupling agents (which are also potentially of use: carbodiimides like DCC, DIC, EDC; uronium-based reagents: HATU, HBTU; phosphonium-based: BOP, PyBOP...) Good luck!
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