Crystal and molecular structure of voacangine: An alkaloid fromStemmadenia Donnell-Smithii

C₂₂H₂₈N₂O₃,M _r=368.5, orthorhombic, D ₂ ⁴ -P2₁2₁2₁. Unit cell dimensions at 293 K area=8.753(3),b=9.252(2),c=24.422(7) Å,V=1978(1) ų,D _c=1.24 g cm^–3, andZ=4. The structure has been determined from single-crystal data collected with a four-circle diffractometer and refined from 1562 reflections down toR=0.050 andwR=0.055. The structural features determined from chemical and spectroscopic studies are confirmed and extended. The stereochemistry at C(4) and C(18) is 4S and 18S. The indole ring is not planar and the seven-membered nitrogen-containing ring adopts a distorted-chair conformation. The indole and seven-membered rings lie on the same plane with a dihedral angle of 0.7 (1)°, while the C(5)-N(6)-C(19)-C(2) atoms of the central axis of the iso-quinuclidine tricyclic structure is perpendicular to seven-membered ring dihedral angle is 92.7 (1)°]. The packing in the crystal is entirely due to van der Waals forces.