7-[(7S)-7-Azaniumyl-5-azaspiro[2.4]hept-5-yl]-8-chloro-6-fluoro-1-[(1S,2R)-2-fluorocyclopropyl]-4-oxo-1,4-dihydroquinoline-3-carboxylate methanol monosolvate

Sitafloxacin is a newly developed fluoroquinolone antibacterial drug. The crystal studied, C19H18ClF2N3O3·CH3OH, consists of one molecule of sitafloxacin and one methanol solvent molecule. The molecule of sitafloxacin is a zwitterion with a protonated primary amine group and a deprotonated carboxylate group. The cyclopropane ring and the CO2 group make dihedral angles of 79.5 (3) and 35.4 (4)°, respectively, with the fused ring system. The supramolecular structure is defined by N—H⋯O and O—H⋯O hydrogen bonds.

Sitafloxacin is a newly developed fluoroquinolone antibacterial drug. The crystal studied, C 19 H 18 ClF 2 N 3 O 3 ÁCH 3 OH, OH, consists of one molecule of sitafloxacin and one methanol solvent molecule. The molecule of sitafloxacin is a zwitterion with a protonated primary amine group and a deprotonated carboxylate group. The cyclopropane ring and the CO 2 group make dihedral angles of 79.5 (3) and 35.4 (4) , respectively, with the fused ring system. The supramolecular structure is defined by N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds.
supplementary materials Acta Cryst. (2012). E68, o2794 [doi:10.1107/S160053681203632X]  Three hydrate forms (hemihydrate, monohydrade and sesqiuhydrate) and three anhydrate forms (alpha,beta and gamma forms) of sitafloxacin crystals have been found so far. The polymorphic and pseudopolymorphic crystals show different physicochemical properties (Yamazaki et al., 1998, Suzuki et al., 2000. The crystal structures of the beta form, the monohydrate and the sesquihydrate have been already reported (Yamazaki et al., 1998, Suzuki et al., 2000. Preparation of the title compound has been reported earlier (Suzuki et al., 2010). In this paper, we report the X-ray crystal structure of the title compound. All donor H atoms are involved in the hydrogen bonding as well as all acceptor O atoms with exception made for O1, Table 1.

Experimental
The preparation of the titled compound was made following a similar procedure described earlier (Suzuki et al., 2010). Slow evaporation gave needle-like crystals suitable for X-ray analysis.

Refinement
The asymmetric unit was selected so that the molecule and the methanol solvent form a hydrgen bonded unit. All  The molecular structure of the title compound showing the atom numbering scheme. Hydrogen bonds are shown as dashed lines and displacement ellipsoids are drawn at the 50% probability level.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 R-factors(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.