Advanced SSNMR techniques, FTIR and XRD applied to polymorphism in a pharmaceutical compound.

GARRO LINCK YAMILA; CHATTAH ANA KARINA; ROMAÑUK CAROLINA BEATRIZ; OLIVERA MARIA EUGENIA; BAGGIO ROBERTO; GARLAND MARÍA TERESA; CUFFINI SILVIA LUCIA; MANZO RUBEN HILARIO; MONTI GUSTAVO

Angra dos Reis

Encuentro; 12th Nuclear Magnetic Resonance Users Meeting / 3rd Iberoamerican NMR Meeting; 2009

Nuclear Magnetic Resonance Meeting

Polymorphism has been recognized as an important element of drug development.1 The fluoroquinolone (FQ) Ciprofloxacin (CIP) is a widely prescribed broad-spectrum oral antibiotic. Saccharin (SAC) is one of the best known and most widely used artificial sweetening agents.  Also, it has been proposed that it could be used to improve organoleptic properties of drugs. New pharmaceutical derivatives of fluoroquinolones with SAC having sweet taste, have been recently reported.2 In the present work we characterize the CIP-SAC form II, which is compared with the previously reported form (I).2 CIP-SAC (II) was successfully obtained as a single-crystal. FTIR patterns of CIP-SAC (II) display the characteristic absorption bands of SAC and each FQ, showing their multicomponent crystalline composition. The N(21)-H band and the bathocromic shift of C(29)=O are a good insight of salt formation by proton transference from SAC amide to the FQ. In the case of CIP, the C(3a)=OOH band is not present. However, this band is present in CIP-SAC and also in the physical mixture. Then, the zwitterionic character of CIP is reverted by proton transference from SAC after salt formation. CIP-SAC (I) and (II), present similar behavior in DSC curves. Fusion is followed by decomposition in both cases. TGA curve gives evidence that there is no loss of weight before fusion in both cases. Then we can conclude that the compounds are obtained as pure and anhydrous solids, without presence of precursors. Comparing CIP-SAC XRPD with their respective precursors new reflections can be observed as well as the absence of characteristic intense reflections of SAC and CIP in the saccharinates. The analysis of the diffraction diagrams reveals that CIP-SAC (II) is a different crystalline form than the previously reported form (I). From Single crystal x-ray diffraction we can see that the structure of CIP-SAC (II) is characterized by conventional (O-H…O, N-H…O and N-H…N) and non-conventional (C-H…O) hydrogen bonds, as well as  interactions. The first one is intramolecular, the second connects the two reference molecules into a single unit. The remaining two interactions involve the positively charged piperazinium N atom in CIP and the two oxygens of the SO2 group in the saccharinate ion, to define a columnar structure. These columnar structures, in turn, approach each other with interleaved aromatic rings pertaining to the CIP unit, in a typical interaction defining 2D structures.  13C CPMAS CIP spectrum gives evidence that it is a zwitterionic crystal.3,4 CIP-SAC (I and II) spectra display narrower lines than CIP, giving evidence of high degree of crystallinity and order. CIP-SAC (II) spectrum confirms that there is only one molecule per asymmetric unit.  This fact marks a difference with the previously reported form I where the multiplicity for each carbon resonance is indicative of more than one molecule per asymmetric unit (see Fig. 1). CIP-SAC spectra show that it is not the physical mixture of CIP and SAC and there are not residues of the precursors. The resonance shifts observed in CIP-SAC (I) can also be observed in CIP-SAC (II): for example the shifts in C(3), C(10), C(28), C(29). Then the interactions found for the single crystal (form II) with the combination of RX and NMR data, can be extrapolated to form I. 2D 1H–13C heteronuclear correlation (HETCOR) spectra in solid state were recorded for all the samples.  The 1H–13C correlations allowed us to make the tentative assignment of the 1H spectra. In agreement with the FTIR data, the proton of the carboxylate group H(3a), does not appears in the solid state 1H spectra of CIP which is in agreement to the zwitterionic character of this compound. On the other hand, this carboxylate proton appears in CIP-SAC 1H spectrum (see Fig. 2), confirming that the zwitterionic character was reverted by salt formation. The polar environment in the piperazine ring of zwitterionic CIP is not significantly affected after salt formation. This fact is supported by the minor changes observed in the protons positions of CIP-SAC spectrum. Besides, protons in the aromatic rings H(2), H(5) and H(8), show clear shifts in all FQ-SACs suggesting new interactions occurring in the saccharinate. A similar behavior was observed by other authors and attributed to changes in hydrogen bonds or – interactions. CIP-SAC (II) was studied and compared with form I previously reported. The solid state techniques used in this work allow the successful characterization of polymorphic forms of pharmaceutically relevant compounds in solid state.