N,N,N-Trimethyl-N-(methyl 5-deoxy-2,3-O-isopropylidene-β-d-ribofuranosid-5-yl)ammonium 4-methylbenzenesulfonate sesquihydrate

The structure of the title compound, [C12H24NO4][C7H7O3S]·1.5H2O, contains alternating layers parallel to (001) of hydrophobic and polar character, stabilized by C—H⋯O hydrogen bonding. The furan ring adopts an envelope conformation with the C(OMe) atom as the flap, and the dioxolane ring is twisted about one of the O—C(methine) bonds. A comparison to related compounds is presented. The tosylate-O atoms were disordered over two positions with the major component having a site occupancy factor = 0.566 (12). The structure was refined as a rotary twin with regard to rotation about the c axis with the contribution of the second component being 0.0048 (6). Solvate water molecules are highly disordered and were removed using the SQUEEZE procedure; the unit cell characteristics take into account the presence of the disordered solvent. High-resolution 1H and 13C NMR spectroscopic data are also presented.

Without doubt, QACs are used worldwide in industry, agriculture, healthcare and the home. Recent years have witnessed a resurgence of interest in the synthesis of QACs, especially their sugar derivatives, which have potential biological properties (Abel et al., 2002;Blizzard et al., 2002;Honda et al., 1988;Thomas et al., 2009;Maslov et al., 2010).
One of our current research objectives is to find a correlation between the structure of the substituents around the quaternary nitrogen atom and the biological activity of the compounds concerned (Dmochowska et al., 2011;Pellowska-Januszek et al., 2004). The synthesis of QACs possessing a substituent that would increase the solubility of these salts appears to be interesting, and the incorporation into the QAC molecule of such a natural entity as a sugar unit could be very effective.
Their structures were determined by NMR. Here we report the X-ray structure of the product with NMe 3 .

Description of the X-ray structure
Crystals belong to the monoclinic system, space group P2 1 . The asymmetric unit of (4) contains one tertiary ammonium cation and one tosyl anion and one and half molecules of solvate water (Fig. 2). The charged parts of both ions are directed towards the middle of the cell, forming a hydrophilic layer, perpendicular to the c axis (Fig. 3). The structure is reinforced by non-conventional C-H···O hydrogen bonds, which are formed perhaps due to the strong acceptor properties of anionic oxygen atoms (see Table 1). The region of disordered solvent is located in the hydrophilic layer and use of SQUEEZE recovered 16.8 efrom a void of volume V = 101.8 Å 3 . Electron density, found in the void, was interpreted as coming from one and half molecules of water per one ionic pair. Naturally, this leads to formation of additional hydrogen bonds in the hydrophilic layer.
Noteworthy, C1 atom is substituted by the methoxy group which may be the reason for increased stability of the conformation. In the analogous compound, substituted by hydrogen at position 1, not a carbon atom but an oxygen atom defined the envelope (see Table 2). Apparently, the opposite is true for compounds without the protection of OH groups.
However, electrostatic forces also contribute significantly to the free energy balance, leading in the case of iodide to formation of the twisted furan ring.

Refinement
All hydrogen atoms were refined as riding with C-H distances in the range 0.95-1.00 Å and thermal ellipsoids U iso (H) = 1.5 U iso (C) for methyl groups or U izo (H) = 1.2 U iso (C) for aromatic or tertiary hydrogen atoms. Oxygen atoms of the tosyl group were refined as disordered over two positions with occupancies of 0.434 (12) and 0.566 (12). Bonds S-O in the tosyl group were constrained to be all equal. The structure was refined as a rotary twin with regard to rotation about the c axis with a small contribution of the second component of 0.0048 (6); R-indices with no twinning were wR 2 = 0.143 and R 1 = 0.052. Structure contains voids at x,y,z (0, 0, 1/2) filled with a disordered solvent, which is difficult to model. Use of program SQUEEZE (Spek, 2009) revealed electron density in that place equivalent to 16.8 e -, and volume of the void of ca 102 Å 3 . It can be attributed to the presence of one and half strongly disordered water molecule positioned in the hydrophilic layer. Three peaks in the asymmetric unit in the region could be found which may mean that position of water molecules can be coupled with the local disorder of the tosyl group oxygen atoms. The original reflection data were corrected for this electron density by the mentioned program. The formula, formula weight, F(000), density and absorption coefficient were corrected for water content in the CIF file. Conformational analysis parameters were calculated using PLATON program by Spek (2009).

Special details
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (