Novel pseudopolymorph of the active metabolite of perindopril

The dimethyl sulfoxide hemisolvate of perindoprilat [sys­tem­atic name: (1S)-2-((S)-{1-[(2S,3aS,7aS)-2-carb­oxy­octahydro-1H-indol-1-yl]-1-oxopropan-2-yl}aza­nium­yl)pentanoate di­methyl sulfoxide hemisolvate], C₁₇H₂₈N₂O₅·0.5C₂H₆OS, an active metabolite of perindopril, has been synthesized, structurally characterized by single-crystal X-ray diffraction and compared with its ethanol disolvate analogue [Pascard et al. (1991). J. Med. Chem. 34, 663–669]. Both compounds crystallize in the ortho­rhom­bic P2₁2₁2₁ space group in the same zwitterionic form, with a protonated alanine N atom and an anionic carboxylate group at the n-alkyl chain. The three structural units present in the unit cell (two zwitterions and the solvent mol­ecule) are held together by a rich system of O—H...O, N—H...O and C—H...O hydrogen-bond con­tacts.