N-{(2S)-3-Hydroxy-4-[(5-methyl-1,3,4-thiadiazol-2-yl)sulfanyl]-1-phenyl-2-butyl}-4-methylbenzenesulfonamide

The thiadiazoyl and sulfonyl-benzene rings in the title compound, C20H23N3O3S3, are aligned to the same side of the molecule, forming a twisted ‘U’ shape [dihedral angle = 77.6 (5)°]. The benzyl-benzene ring is orientated in the opposite direction from the molecule but projects approximately along the same axis as the other rings [dihedral angle between benzene rings = 28.2 (5)°] so that, overall, the molecule has a flattened shape. The hydroxy and amine groups are almost syn which enables the formation of intermolecular hydroxy-OH⋯N(thiadiazoyl) and amine-H⋯O(sulfonyl) hydrogen bonds leading to a supramolecular chain aligned along the a axis.

The thiadiazoyl and sulfonyl-benzene rings in the title compound, C 20 H 23 N 3 O 3 S 3 , are aligned to the same side of the molecule, forming a twisted 'U' shape [dihedral angle = 77.6 (5) ]. The benzyl-benzene ring is orientated in the opposite direction from the molecule but projects approximately along the same axis as the other rings [dihedral angle between benzene rings = 28.2 (5) ] so that, overall, the molecule has a flattened shape. The hydroxy and amine groups are almost syn which enables the formation of intermolecular hydroxy-OHÁ Á ÁN(thiadiazoyl) and amine-HÁ Á ÁO(sulfonyl) hydrogen bonds leading to a supramolecular chain aligned along the a axis.

N-{(2S)-3-Hydroxy-4-
In (I), Fig. 2, the thiadiazoyl and sulfonyl-benzene rings are orientated to the same side of the molecule but are not aligned in a parallel fashion as seen in the dihedral angle of 77.6 (5) ° formed between the rings. The benzyl-benzene is directed away from the rest of the twisted U-shaped molecule and forms a dihedral angle of 28.2 (5) ° with the sulfonyl-benzene ring. The key stereochemical feature of the molecule is the almost syn alignment of the hydroxyl and amine groups. This has an important consequence in the crystal packing.
As seen from Fig. 3, molecules assemble into a supramolecular chain via hydroxyl-OH···N(thiadiazoyl) and amine-H···O(sulfonyl) hydrogen bonds, Table 1. The chains are aligned along the a axis and assemble in the crystal structure without any specific interactions between them, Fig. 4.

Experimental
Referring to Fig. 1, trifluoroacetic acid (1.5 ml, 20 mmol) was added to a solution of 2 (2 mmol), prepared from 1 and 5-methyl-1,3,4-thiadiazole-2(3H)-thione, in CH 2 Cl 2 (6 ml). The mixture was stirred for 6 h, rotary evaporated to leave a residue, which was dissolved in EtOAc (20 ml), successively washed with 5% NaHCO 3 aqueous solution, water and brine, and dried over MgSO 4 . The solvent was removed to afford the corresponding free amine, which was dissolved in EtOAc (10 mL) to which were added triethylamine (2.2 mmol) and N,N-dimethylformamide (0.2 mmol). The system was stirred for 30 minutes under nitrogen and p-toluenenesulfonyl chloride (2.0 mmol) was slowly added. The mixture was stirred for 8 h, successively washed with 5% HCl aqueous solution, water and brine, and dried over MgSO 4 . The solvent was removed in high vacuum and the title product 3 was obtained in 68% yield after recrystallization from hexane. The crystals used in the structure determination were grown from EtOH solution.  1330, 1161 (O═S═O); 686 (C-S).
The O-and N-bound H atoms were located from a difference map and refined with the distance restraints O-H = 0.84 ± 0.01 and N-H = 0.88±0.01 Å, and with U iso (H) = zU eq (carrier atom); z = 1.5 for O and z = 1.2 for N. The refinement of the Flack absolute sturcture was ambiguous [refined value = 0.24 (19)] and 1482 Friedel pairs were averaged in the final refinement and the absolute configuration was assigned on the basis of the chirality of the L-serine starting material. The small (0.02 x 0.02 x 0.14 mm) needle was weakly diffracting but it was not deemed necessary to secure a data set with synchrotron radiation. The poor nature of the sample is also reflected in the relatively high values of R int and in the residuals. However, the structure has been determined unambiguously.

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 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.