2-(4-Acetamidobenzenesulfonamido)-3-methylbutanoic acid

In the title compound, C13H18N2O5S, the benzene ring and the acetamide group are almost coplanar [dihedral angle = 5.6 (3)°], and the amine group projects almost vertically from this plane [C—C—S—N = −84.5 (7)°]. A short intramolecular C—H⋯O contact occurs. In the crystal, O—H⋯O, N—H⋯O and N—H⋯(O,O) hydrogen bonds lead to a three-dimensional network. One of the methyl groups of the isopropyl residue is disordered over two orientations in a 0.747 (16):0.253 (16) ratio.

In the title compound, C 13 H 18 N 2 O 5 S, the benzene ring and the acetamide group are almost coplanar [dihedral angle = 5.6 (3) ], and the amine group projects almost vertically from this plane [C-C-S-N = À84.5 (7) ]. A short intramolecular C-HÁ Á ÁO contact occurs. In the crystal, O-HÁ Á ÁO, N-HÁ Á ÁO and N-HÁ Á Á(O,O) hydrogen bonds lead to a threedimensional network. One of the methyl groups of the isopropyl residue is disordered over two orientations in a 0.747 (16):0.253 (16) ratio.

Comment
Sulfonamide drugs are widely used for the treatment of certain infections caused by Gram-positive and Gram-negative microorganisms, some fungi, and certain protozoa (Korolkovas, 1988;Mandell & Sande, 1992). In continuation of structural investigations of sulfonamides (Sharif et al., 2010;Khan et al., 2010), herein, the crystal structure of title compound, (I), is described.
The structure analysis of (I), Fig. 1, shows that the acetamide group is co-planar with the benzene ring to which it is attached; the dihedral angle = 5.6 (3) °. This conformation is stabilised by an intramolecular C-H···O contact, Table 1. While the S atom also lies in this plane [the S1-C1-C2-C3 torsion angle = 176.8 (7) °], the sulfonamido-O atoms lie to one side [being displaced by 0.386 (5) Å for atom O1 and 0.555 (6) Å for O2] and the amine substituent to project almost vertically to the other [the N2-S1-C1-C2 torsion angle = -84.5 (7) °]. Within the amine group, the carboxylic acid group is folded back to lie over the benzene ring; the dihedral angle between the two planes = 34.2 (5) °.
The crystal structure is stabilised by O-H···O and N-H···O hydrogen bonding interactions, Table 1. Thus, the carboxylic acid-hydroxyl group forms a donor interaction to the amide-carbonyl, and each of the N-H atoms forms a donor interaction to a sulfonamido-O; an intramolecular interaction formed between the N2-H and carboxylic acid-carbonyl group is also noted, Table 1. The result of the hydrogen bonding just described is the formation of a 3-D network, Fig. 2.

Experimental
To 2-amino-3-methylbutanoic acid (0.339 g, 2.8 mmol ) in distilled water (10 ml) was added 4-acetylaminobenzenesulfonyl chloride (0.7 g, 2.8 mmol) with stirring at room temperature, while maintaining the pH of the reaction mixture at 8 using 3% sodium carbonate. The progress of the reaction was monitored by TLC. On completion of reaction, the pH was adjusted to 3.0 by slow addition 3 N HCl. The precipitate formed in this way was washed with water, dried and recrystalized from methanol and ethyl acetate mixture (50:50 v/v) to yield colourless prisms of (I); m. pt. 510 K.