1,2-Dimethoxy-12-methyl-13H-[1,3]benzodioxolo[5,6-c]phenanthridine

The crystal structure of the benzophenanthridine alkaloid dihydrochelerythrine (1,2-dimethoxy-12-methyl-13H-[1,3]benzodioxolo[5,6-c]phenanthridine), C21H19NO4, was determined by single-crystal X-ray diffraction analysis. The alkaloid was isolated from the stem bark of Zanthoxylum usambarense (Engl.) Kokwaro (Rutaceae), collected from Nairobi, Kenya. In contrast to the earlier reported semisynthetic form, which crystallised in the monoclinic space group P21/c, the present natural isolate adopts the orthorhombic Pbca space group. The molecule displays an approximately planar benzophenanthridine framework, but with the dihydro group resulting in a distinctly puckered ring and an out-of-plane methyl group on the tertiary amine. Non-covalent interactions are responsible for the characteristic herringbone packing motif.