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The crystal structures of three solvates of zafirlukast [systematic name: cyclopentyl N-{1-methyl-3-[2-methyl-4-(o-tolylsulfonylaminocarbonyl)benzyl]-1H-indol-5-yl}carbamate], viz. the monohydrate, C(31)H(33)N(3)O(6)S.H(2)O, (I), the methanol solvate, C(31)H(33)N(3)O(6)S.CH(3)OH, (II), and the ethanol solvate, C(31)H(33)N(3)O(6)S.C(2)H(5)OH, (III), have been determined by single-crystal X-ray diffraction analysis. All three compounds crystallize in the monoclinic crystal system. Zafirlukast adopts a similar Z-shaped conformation in all three solvates. The methanol and ethanol solvates are isostructural. The packing of the zafirlukast molecules in all three crystal structures is similar and is expressed by hydrogen-bonded molecules that are related by translation, along (101) in (I) and along the b axis in (II) and (III). The methanol and ethanol solvent molecules are hydrogen bonded to two molecules of zafirlukast. The water molecule, on the other hand, acts as a connector via hydrogen bonds between three molecules of zafirlukast. The solvent molecules are not released at temperatures below the melting points of the solvates.

The preparation of the compounds (II) and (VIII) has been described earlier.

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