Solution Conformation of [D-Pen2,D-Pen5]enkephalin in Water: A NMR and Molecular Dynamics Study

The solution conformation of [D -Pen²,D -Pen⁵] enkephalin (DPDPE), a highly potent δ-selective opioid agonist, was examined by means of NMR, molecular mechanics and molecular dynamics methods. The structural information in the solvent water was obtained employing one- and two-dimensional methods of ¹H and ¹³C-NMR spectroscopy. Based on the distance geometry technique using the ROE data as input, 400 conformers were obtained and considered in the structure analysis. Alternatively, about 2000 conformers were stochastically generated and related to the NMR data after energy minimization. The structure analysis provides one conformer in agreement with all NMR data, which belongs to the lowest energy conformation group. This structure may serve as a reference conformer for DPDPE analogues synthesized with the aim of activity increase.