Isolation and Characterization of an Impurity Obtained During the Synthesis of the Antibiotic Drug Sparfloxacin

Abstract

During the synthesis of Sparfloxacin, a fluoroquinolone antibiotic drug, an unknown impurity (SF5-IMP) was identified in the fifth stage of the synthetic process. The impurity has been isolated from the mother liquor of intermediate SF5. The mother liquor was concentrated to dryness added dichloromethane and stirred for 1 h and filtered to generate SF5-IMP and the molecular structure was elucidated as 7-amino-1-cyclopropyl-5,6,8-trifluoro-4-oxo-1,4-dihydroquinoline-3-carboxylic acid by 19 F NMR and single crystal X-ray diffraction studies. The structural features of SF5-IMP and SF5 have been discussed here.

Isolation and structure elucidation of unexpected in‐process impurities during tetrazole ring formation of an investigational drug substance

“…The addition of the NH to the top part of the molecule would support the fact that the isolated in-process impurity B with [M+H] + at 477 Da has two distinct carbonyl carbons (δ, 155.6 and 169.3 ppm) ( Fig. 10) for the two dimethylcarbamoyl moieties by contrast to the isolate in-process impurity A with [M+H] + at 462 Da, which is symmetrical in the 2,8-bis(dimethylcarbamoyl)-10,11-dihydro-5H-dibenzo[a,d] [7]annulen-5-yl portion of the molecule. The NMR data supported the structure presented in Fig.…”

“…However, the pseudo-symmetry of the isomers shown in Figs 15 and 16 and the near identity of the chemical shifts of the (Tables 3 and 4) make exact determination of whether the additional NH groups are located on the left-side or right-side phenyl rings. As the pseudo-symmetry of the N,N,N′,N′-tetramethyl-10,11dihydro-5H-dibenzo[a,d] [7]annulene-2,8-dicarboxamide-5-yl is broken by the addition of an NH in one of the dimethylcarbamoyl groups, the structure of the minor isolated in-process impurity D with [M+H] + at 577 Da was proposed as depicted in Fig. 16 with the NH in the other dimethylcarbamoyl group.…”

“…The knowledge of the structures of in-process impurities may provide a better understanding of the reactions and their mechanistic formations with the potential to design better the synthesis of the product of interest. [3][4][5][6][7][8] An investigational drug substance for the treatment of diabetes was being scaled-up to support Phase 2 clinical trials. In one of the steps of the synthesis that required the formation of a tetrazole ring in an intermediate ( Fig.…”

“…Isolation of in‐process impurities from the mother liquor is not trivial because of complex mixtures of numerous components of the reaction. The knowledge of the structures of in‐process impurities may provide a better understanding of the reactions and their mechanistic formations with the potential to design better the synthesis of the product of interest …”