Crystal and molecular structure of 1-epi-delphisine and nmr assignments for delphisine, 1-epi-delphisine and delphinine

Abstract

The crystal and molecular structure of the norditerpenoid alkaloid 1-epi-delphisine (5), C₂₈H₄₃NO₈, M_r 521.66, has been confirmed by as X-ray diffraction study using the SIR 88 analysis program. The alkaloid crystallizes in the space group P2₁ with cell parameters: a = 11.853(1)Å, b = 10.511(1)Å, c = 11.854(1)Å, β= 112.58(1), V = 1363.61(0)ų, Z = 2, D_calc = 1.27 g/cm³, λ (Cu Kα) = 1.54184 Å, μ(Cu Kα = 7.2 cm⁻¹, F(000) = 564, temperature 23°C, R = 0.052, for 2907 reflections. Ring A of 1-epi-delphisine exists in a chair conformation. By comparison, delphisine which bears a C-1 α hydroxyl group, has ring A in a boat conformation stabilized by an intramolecular N----H-O hydrogen bond. Ring D of both of these alkaloids exists in a boat form. Unambiguous proton and carbon-13 nmr assignments for delphisine, 1-epi-delphisine and delphinine have been made by a detailed analysis of the DEPT, COSY, HETCOR, COLOC, DIFNOE, and selective INEPT nmr techniques.