Molecular and crystal structures of (C)-homochelidonine, (C)-chelamine, and (K)-norchelidonine

The molecular and crystal structures of three hexahydrobenzo[c]phenanthridine alkaloids (C)-homochelidonine (1), (C)-chelamine (2), and (K)-norchelidonine (3) have been examined by X-ray single crystal diffraction and by CD spectroscopy. All alkaloids 1–3 possess the cis-junction of B/C rings and the C11-hydroxyl in axial position on the half-chair-conformated B ring. The dihedral angles between the aromatic planes A, D are 51.9, 55.0/44.8, and 22.08 in 1, 2, and 3, respectively. In all compounds 1–3, there is intramolecular H-bonding between C11–OH group and nitrogen. Using a combined approach of X-ray diffraction and CD spectra correlations the absolute configurations of the title alkaloids have been determined as (C)-11S,13R,14S-homochelidonine (1), (C)-11R,12R,13R,14S-chelamine (2), and (K)-11R,13S,14R-norchelidonine (3). q 2004 Elsevier B.V. All rights reserved