Abstract
The asymmetric unit of the title compound, C28H38N4O8·C2H6OS, contains one tetrapeptide and one disordered dimethyl sulfoxide (DMSO) molecule. The central five-membered ring (Pro2) of the peptide molecule has a disordered envelope conformation [occupancy ratio 0.879 (2):0.121 (2)] with the envelope flap atom, the central C atom of the three ring methylene groups, lying on alternate sides of the mean ring plane. The terminal five-membered ring (Pro4) also adopts an envelope conformation with the C atom of the methylene group closest to the carboxylic acid function as the envelope flap, and the six-membered tetrahydropyrane ring shows a chair conformation. The tetrapeptide exists in a helical conformation, stabilized by an intramolecular hydrogen bond between the amide N-H group of the heterocyclic [alpha]-amino acid Thp and the amide O atom of the 4-methoxybenzoyl group. This interaction has a graph set motif of S(10) and serves to maintain a fairly rigid [beta]-turn structure. In the crystal, the terminal hydroxy group forms a hydrogen bond with the amide O atom of Thp of a neighbouring molecule, and the amide N-H group at the opposite end of the molecule forms a hydrogen bond with the amide O atom of Thp of another neighbouring molecule. The combination of both intermolecular interactions links the molecules into an extended three-dimensional framework.
Stoykova, Svetlana A