(2R,3R)-N-(4-Chlorophenyl)-2,3-dihydroxy-N′-(5-phenyl-1,3,4-thiadiazol-2-yl)succinamide

In the structure of the title compound, C18H15ClN4O4S, the dihedral angle between the two benzene rings is 1.4 (3)°. The angle between the phenyl ring and thiadiazole ring is 5.8 (4)°. The conformations of the N—H and C=O bonds are anti with respect to each other. In the crystal structure, molecules are linked by intermolecular O—H⋯N, N—H⋯O and O—H⋯O hydrogen bonds, forming a three-dimensional network.

In the structure of the title compound, C 18 H 15 ClN 4 O 4 S, the dihedral angle between the two benzene rings is 1.4 (3) . The angle between the phenyl ring and thiadiazole ring is 5.8 (4) . The conformations of the N-H and C O bonds are anti with respect to each other. In the crystal structure, molecules are linked by intermolecular O-HÁ Á ÁN, N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds, forming a three-dimensional network.

Comment
The present tartaric acid derivate is in continuation to our previously reported crystal structure of thiadiazole scaffold compounds (Li et al., 2008). The title compound ( Fig. 1) was synthesized according to literature procedures (Marson & Melling 2005;Tu et al., 2008;Shriner & Furrow 1995) and crystallized in the monoclinic crystal system. The dihedral angle between the two benzene rings is 1.4 (3)°; the angle between the benzene ring (C7-C12) and thiadiazole ring is 5.8 (4)°. The conformations of the N-H and C=O bonds are anti with respect to each other. Bond lengths and angles are in normal ranges and comparable to those in related structures (Watadani et al., 2005). In the crystal structure, molecules are linked by intermolecular O-H···N, N-H···O and O-H···O hydrogen bonds forming a three-dimensional network (Table 1, Figure 2).
After the mixture was stirred at room temperature for 16 h, N,N-dicyclohexylcarbodiimide (9 mmol) and p-chloroaniline (9 mmol) in THF were added to the mixture. The reaction mixture was stirred at room temperature overnight. After insoluble material was filtered off the filtrate was evaporated in vacuo. The residual was hydrolyzed by a solution of K 2 CO 3 in methanol at 65°C for 2 h and recrystallized from THF to afford the target compound. Yield: 3.06 g, 81%, m.p. 221-222°C.
Colorless block-shaped single crystals of the title compound suitable for X-ray diffraction analysis precipitated after several days.

Refinement
H atoms were positioned geometrically and refined using a riding model, with C-H = 0.93-0.96 Å, O-H = 0.82-0.85 Å and N-H = 0.86 Å, U iso (H) = 1.2U eq (C,N), and 1.5U eq (O). The absolute configuration is undoubtly as described since enantiomerically pure starting compounds were used and the reaction conditions are not considered to lead to racemisation or inversion.

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.