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Updated: Jul 9, 2026

Application and Methodology of the Non-destructive 19F Time-domain NMR Technique to Measure the Content in Fluorine-containing Drug Products
Published on: August 22, 2017
Monohydrous dihydrogen phosphate salts of norfloxacin and ciprofloxacin
Benyong Lou1, Dan Boström, Sitaram P Velaga
1Department of Health Science, Luleå University of Technology, Luleå S-971 87, Sweden.
Abstract:
Norfloxacin and ciprofloxacin crystallize with phosphoric acid in aqueous solution to give the salts 4-(3-carboxy-1-ethyl-6-fluoro-4-oxo-1,4-dihydro-7-quinolyl)piperazinium dihydrogenphosphate monohydrate, C16H19FN3O3(+) x H2PO4(-) x H2O, and 4-(3-carboxy-1-cyclopropyl-6-fluoro-4-oxo-1,4-dihydro-7-quinolyl)piperazinium dihydrogenphosphate monohydrate, C17H19FN3O3(+) x H2PO4(-) x H2O, respectively. In the crystal structures, the phosphate anions and the piperazine rings of norfloxacin or ciprofloxacin form a 12-membered supramolecular synthon, viz. R4(4)(12). The synthons R4(4)(12) and R2(2)(8) formed between adjacent phosphate anions result in the three-dimensional structures.
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