(2S)-3-(1H-Indol-3-yl)-2-(4-methylbenzenesulfonamido)propionic acid monohydrate

In the title compound, C18H18N2O4S·H2O, the indole and toluene ring systems are oriented at a dihedral angle of 84.51 (9)°. In the crystal, the components are linked by N—H⋯O, O—H⋯O, C—H⋯O and N—H⋯π interactions. These include a short link from the α-C atom of the amino acid fragment.

In the title compound, C 18 H 18 N 2 O 4 SÁH 2 O, the indole and toluene ring systems are oriented at a dihedral angle of 84.51 (9) . In the crystal, the components are linked by N-HÁ Á ÁO, O-HÁ Á ÁO, C-HÁ Á ÁO and N-HÁ Á Á interactions. These include a short link from the -C atom of the amino acid fragment.

Related literature
For details of the synthesis, see: Deng & Mani (2006). For background to sulfonamides in biology, see: Parka et al.   Table 1 Hydrogen-bond geometry (Å , ).

D-HÁ
The configuration of the stereogenic carbon atom, C7, is S, which is consistent with that of the equivalent atom in the starting material.
In the crystal structure, the components are linked by a variety of interactions (Table 1). The carboxylic acid makes an O-H···O hydrogen bond to the water molecule, and the water molecule is involved in the same type of hydrogen bond to the sulfonyl group, to generate alternating [110] chains of the two species. The amino-acid N-H group forms an intermolecular link to the sulfonyl group. The indole N-H group forms an N-H···π bond to the six-membered ring of the indole system of an adjacent molecule. Two C-H···O interactions are also present; a strong link from the α-carbon atom, C7, as also seen in related structures (Khan et al., 2011) and a weaker link from the methyl group.

Experimental
The title compound was prepared following the literature method (Deng & Mani, 2006) and recrystalized from methanol by slow evaporation to yield colourless needles.

Refinement
The C-bound H-atoms were positioned with idealized geometry with C-H = 0.93 Å for aromatic, C-H = 0.96 Å for methyl, C-H = 0.97 Å for methylene, C-H = 0.98 Å for methine, and were refined using a riding model with U iso (H) = 1.2 U eq (C) but U iso (H) = 1.5 U eq (C) for methyl.
The hydroxyl H-atom of the carboxylic acid group was also positioned with idealized geometry, O-H = 0.82 Å, and refined as riding with U iso (H) = 1.5 U eq (O).
The H atoms of the water molecule were located in a difference map with O-H = 0.893-0.900Å, and refined as riding The H atoms attached to N were located in a difference map and refined freeely. Fig. 1. The molecular structure of the title compound, with displacement ellipsoids drawn at the 50% probability level. Hydrogen atoms are shown as spheres of arbitrary radius.