(2R)-2-Cinnamoylamino-N-[5-(4-methoxyphenyl)-1,3,4-thiadiazol-2-yl]propanamide

The asymmetric unit of the title compound, C21H20N4O3S, contains two independent molecules. The dihedral angles between the two benzene rings are 47.6 (1) and 30.2 (1)°, the corresponding values between the p-methoxybenzene and thiadiazol rings are 12.3 (1) and 24.7 (1)°, respectively, for the two molecules. The conformations of the N—H and C=O bonds are anti with respect to each other. The enone groups show a trans configuration. The crystal structure is stabilized by N—H⋯O and N—H⋯N interactions. The absolute structure could not be determined from the X-ray data but the absolute configuration has been assigned by reference to an unchanging chiral centre in the synthetic procedure.

The asymmetric unit of the title compound, C 21 H 20 N 4 O 3 S, contains two independent molecules. The dihedral angles between the two benzene rings are 47.6 (1) and 30.2 (1) , the corresponding values between the p-methoxybenzene and thiadiazol rings are 12.3 (1) and 24.7 (1) , respectively, for the two molecules. The conformations of the N-H and C O bonds are anti with respect to each other. The enone groups show a trans configuration. The crystal structure is stabilized by N-HÁ Á ÁO and N-HÁ Á ÁN interactions. The absolute structure could not be determined from the X-ray data but the absolute configuration has been assigned by reference to an unchanging chiral centre in the synthetic procedure.

D-HÁ
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: IM2079).
In view of the importance of these organic materials, the title compound ( Fig. 1) was synthesized (Foroumadi et al., 1999;Levy & Palmer 1942;Song et al., 1992) and its crystal structure is reported here. The asymmetric unit of the title compound, C 21 H 20 N 4 O 3 S, contains two independent molecules. The dihedral angles between the p-methoxybenzene and thiadiazol rings is 12.2 (1) ° and 24.7 (1)°, the corresponding values between the two benzene rings are measured to 47.6 (1)° and 30.2 (1)°, respectively, for the two molecules. The conformations of the N-H and C=O bonds are anti with respect to each other. The enone groups are trans configurated. Bond lengths and angles are in normal ranges and comparable to those in related structures (Gowda et al., 2008;Fun et al., 2008;Thiruvalluvar et al., 2008). In the crystal structure, molecules are linked through intermolecular N-H···O hydrogen bonds forming a three-dimensional network (Table 1, Figure 2).
Experimental N,N-Dicyclohexylcarbodiimide (5.7 mmol) was added to a cooled solution of N-cinnamoyl-D-alanine (5.6 mmol) and Nhydroxysuccinimide (5.6 mmol) in freshly distilled dioxane (30 ml). The reaction mixture was stirred overnight at room temperature. The insoluble material was filtered off and washed with cold dioxane. 2-Amino-5-(4-methoxyphenyl)-1,3,4thiadiazole (5.5 mmol) was added to the filtrate and the reaction mixture was stirred for 48 hr at room temperature. The solvent was removed under reduced pressure. The residual was dissolved in EtOAc and the insoluble material was filtered off. The filtrate was washed successively with saturated Na 2 CO 3 solution (20 ml, x 3), water (20 ml, x 1), 0.1 M HCl (20 ml, x 3) and water (20 ml, x 1). The organic layer was evaporated in vacuo and the residue was recrystallized from methanol (30 ml), yield: 35.2%. 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 using SHELXL97 default values (U ĩso (H) = 1.2 U eq (C) for CH and CH 2 groups and U ĩso (H) = 1.5 U eq (C) for CH 3 ). Refinement with all data (Friedel opposites not merged) led to an unsuitably large error of the Flack parameter. The final refinement was therefore performed with a data set with merged Friedel pairs, hence the calculated Flack parameter is meaningless. The absolute configuration is nevertheless undoubtly as described since enantiomerically pure starting compounds were used and the reaction conditions are not condidered to lead to racemisation or inversion.

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 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. Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )