(4S)-4-Benzyl-N-{[(4S)-4-benzyl-2-oxo-1,3-oxazolidin-3-yl]sulfonyl}-2-oxo-1,3-oxazolidine-3-carboxamide

The title compound, C21H21N3O7S, contains an oxazolidinone ring and a sulfonamide group, both characteristic for biologically and pharrmaceutically active compounds. Both stereogenic centres reveal an S absolute configuration. The two oxazolidinone rings are in an envelope conformation with the methylene carbon flap atoms deviating by 0.428 (1) and 0.364 (2) Å from the best least-square planes formed by the four other ring atoms. An intramolecular N—H⋯O hydrogen bond contributes to the folded conformation of the molecule. In the crystal, weak intermolecular C—H⋯O interactions connect the molecules into helices along the the twofold screw axes.

The title compound, C 21 H 21 N 3 O 7 S, contains an oxazolidinone ring and a sulfonamide group, both characteristic for biologically and pharrmaceutically active compounds. Both stereogenic centres reveal an S absolute configuration. The two oxazolidinone rings are in an envelope conformation with the methylene carbon flap atoms deviating by 0.428 (1) and 0.364 (2) Å from the best least-square planes formed by the four other ring atoms. An intramolecular N-HÁ Á ÁO hydrogen bond contributes to the folded conformation of the molecule. In the crystal, weak intermolecular C-HÁ Á ÁO interactions connect the molecules into helices along the the twofold screw axes.
N-Acylsulfonamide is an important functional group in organic chemistry and is present in many biologically active molecules. They has been incorporated into tested drugs and therapeutic agents for Alzheimer's disease, bacterial infection, osteoporolysis, and cancer (Kang et al. , 2009). Recently, it was reported on the in vitro activity of acylsulfonamide bisoxazolidinone against the virulent strain RH of Toxoplasma gondii and the human lymphocytes (Bouasla et al., 2010).
Those compounds have also been useful in studies of the physical chemistry and the mechanism of action of carbonic anhydrase because of their highly specific interaction with the active site (King & Burgen, 1976). Moreover, sulfonamides containing different donor atoms find use in coordination chemistry (Beloso et al. , 2005). They are also very interesting for studying hydrogen-bonding interactions (Adsmond & Grant, 2001).
Recently, many new heterocyclic sulfonamide derivatives have been synthesised (Yan et al., 2007) and some of them have been optimized as highly selective EP1 receptor antagonists (Naganawa et al., 2006). We report here the molecular structure of a new heterocyclic sulfonamide, (I), derived from R-phenyl alanine which was prepared in order to investigate its potential clinical application.
In the molecule C 21 H 21 N 3 O 7 S, (Fig. 1), the distances and angles around the sulfonamide group are within the expected range of values found in similar structures (Michaux et al. , 2001 -Cherif et al., 2002)suggesting that electronic delocalization is less important for the O atoms of the sulfonamide group in (I) than in the other sulfonamide derivatives. The geometric parameters of the oxazolidinone rings are in a good agreement with those reported in previous similar studies (Cheng et al. , 2005). The non-planarity of the heterocyclic rings is evidenced by the torsion angles of -12.0 (3)° and -12.2 (3)° for C2B-O1B-C1B-N2B and C2A-O1A-C1A-N1A, respectively.
The molecular structure is stabilized by an intramolecular N-H···O hydrogen-bond interaction (Fig. 2) involving the NH group and the carbonyl O atom. In the crystal packing (Fig. 3), molecules are linked by infinite chains of C-H···O hydrogen-bonds (Table 1) running parallel to the b axis and generating a C(9) graph-set motif (Bernstein et al., 1995).
supplementary materials sup-2 Experimental N,N'-acylsulfonamide bis-oxazolidinones are prepared in two steps: carbamoylationand sulfamoylation, from the condensation reaction of oxazolidin-2-one derived from S-phenylalanine with chlorosulfonyl carbamate. The synthesis carried out in two steps: carbamoylation and sulfamoylation, starting from chlorosulfonyl isocyanate and α-hydroxyester.
To a stirred solution of chlorosulfonyl isocyanate (1.62 g, 11.4 mmol) in 20 ml of anhydrous CH 2 Cl 2 at 0°C, was added dropwise 1 equivalent of -hydroxyester (1.34 g, 11.4 mmol) in 5 ml of the same of solvent. After 30 min, the carbamate was added to a solution of oxazolidinine (2.01 g, 11.4 mmol), in presence of 1.1 equivalent of triethylamine at 273 K. The reaction was stirred for less than 1 h at room temperature. The reaction mixture was washed with hydrochloride acid (0.1 N, 2x10 mL) and water (20 mL). Organic layers were dried over anhydrous magnesium sulfate, filtrated and concentrated under vacuum. The residue was purified by chromatography on silica gel eluted by CH 2 Cl 2 to give 17% of carboxylsulfamides and 46% of N-acylsulfonamide bis oxazolidinone as a white solid.
Single crystals suitable for X-ray structure analysis could be obtained by slow evaporation of a concentrated solution in ether at room temperature.

Refinement
All non-H atoms were refined with anisotropic atomic displacement parameters. H atoms were positioned with idealized geometry and refined using a riding model with C-H and N-H bond lengths constrained to 0.93-0.98 and 0.86 Å, respectively. Their isotropic displacement parameters were set equal to 1.2Ueq (parent atom). The title compound crystallizes in the non centrosymmetric space group P2 1 and the absolute configuration is determined from measured Friedel opposites. Fig. 1. ORTEP view of the asymmetric unit of (I) showing 50% probability displacement ellipsoids.

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.
supplementary materials sup-4 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.