Moxifloxacinium chloride monohydrate

The title compound {systematic name: 7-[(1S,6S)-8-aza-2-azoniabicyclo[4.3.0]non-8-yl]-1-cyclopropyl-6-fluoro-8-methoxy-4-oxo-1,4-dihydroquinoline-3-carboxylic acid chloride monohydrate}, C21H25FN3O4 +·Cl−·H2O, crystallizes with two moxifloxacinium cations, two chloride ions and two uncoordinated water molecules in the unit cell. The crystal structure has a pseudo-inversion center except for the chloride ions. In both moxifloxacinium cations, the quinoline rings are approximately planar, the maximum atomic deviations being 0.107 (3) and 0.118 (3) Å. The piperidine rings adopt a chair conformation while the pyrrolidine rings display a half-chair conformation. In the crystal, the carboxyl groups, the protonated piperidyl groups, the uncoordinated water molecule and chloride anions participate in O—H⋯O, O—H⋯Cl and N—H⋯Cl hydrogen bonding; weak intermolecular C—H⋯O and C—H⋯Cl hydrogen bonding is also present in the crystal structure.


Comment
Moxifloxacin hydrochloride, a new fluoroquinolone with a broad spectrum of antibacterial, anaerobes and atypical oranisms (Seidel et al., 2000), is approved by the Food and Drug Administration in December 1999 for use in the treatment of acute bacterial sinusitis, acute bacterial exacerbations of chronic bronchitis, and community-acquired pneumonia caused by susceptible microorganisms (Culley et al., 2001). The crystal structure of moxifloxacin hydrochloride methanol solvate have been reported (Ravikumar & Sridhar, 2006). In the present study, we report the crystal structure of moxifloxacin hydrochloride monohydrate.
The asymmetric unit consists of two independent moxifloxacin cations protonated at the terminal piperidyl N atom, two chloride ions and two lattice water molecules (Fig. 1). The important different of asymmetric unit is the orientation of its piperidinopyrrolidine side chain. In the cation A, the torsion angle of C9-C8-N2-C7 is 35.9 (5)°, while in the cation B, the torsion angle is 168.4 (3)°. So, we can see that the two cations adopt conformations that differ by an almost 180°r otation with respect to the piperidinopyrrolidine side chain. Conformation of the moxifloxacin cations in the structure of title compound and moxifloxacinium chloride-water-methanol solvate (Ravikumar & Sridhar, 2006) shows not much different.
In both moxifloxacin cations of the title compound, the quinoline rings are approximately planar, the maximum atomic deviations being 0.107 (3) and 0.118 (3) Å, respectively. The peridine rings adopt chair conformation with the exposed N atom participating in the hydrogen-bonding interactions, and the pyrrolidine rings favour a half-chair conformation twisted on atoms C1-C5, which is similar to that of moxifloxacinium methanol solvate (Ravikumar & Sridhar, 2006). The cyclopropyl rings are not coplanar with the quinoline ring system, forming the dihedral angles with quinoline ring systems of 73.9 (2) and 74.3 (2)° for cation A and B respectively. The C17-O1 methoxy group is almost perpendicular to the plane of the quinoline ring system [torsion angle of C17-O1-C9-C8 is 94.2 (4)° and -84.1 (4)° for the A and B cations, respectively].
In the crystal structure, different modes of hydrogen-bonding interactions, cation-cation, cation-water, cation-chloride ion and water-chloride ion, stablizing the molecules. Carboxyl atom O3 forms an intramolecular hydrogen bond with carbonyl group O2. This hydrogen bond forms a quasi-six-membered ring. The two H atoms at atom N1 of piperidine ring participate in intramolecular and intermolecular hydrogen bonding with chloride ion. The water molecule acts as a donor in hydrogen bonds with the carbonyl O atom of the carboxylic acid group of cation A, while in the cation B, water molecule forms hydrogen bonds with a chloride ion and the the carbonyl O atom of the carboxylic acid group. In this way, the hydrogen bonds link all of the components of the structure into extented two dimensional networks (Fig.2). Weak intermolecular C-H···O and C-H···Cl hydrogen bonding is also present in the crystal structure.

Experimental
The crude product is supplied by Zhejiang Jingxin Pharmaceutical Co., LTD. It was recrystallized from ethanol solution, giving yellow crystals suitable for X-ray diffraction.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.