Structure, absolute configuration, and conformation of the antimalarial compound, Artemisinin

The crystal and molecular structure of the antimalarial compound Artemisini n (formerly known as Qinghaosu), C15H22-O-5, has been determined by direct methods. Crystals are orthorhombic colorless needles, space group P2(1)2(1) 2(1), Z = 4 D-c = 1.299 g cm(-3), with unit cell parameters a = 6.3543(9), b = 9.439(3), c = 24.066(4) Angstrom. The molecule incorporates a fused rin g system containing a six-membered ring C which includes an oxygen bridge a nd a peroxy-bridge. The ring C has a distorted boat conformation and the C- O-O-C torsion angle is 47.8(2)degrees. Rings A and D have symmetrical chair and distorted chair conformations, repectively. Ring junctions A/B, A/D, a nd C/D are cis, junction B/D is trans. All inter-molecular contacts are van der Waals. The absolute configuration of Artemisinin was determined from t he refined value of the Flack x parameter. [The atomic coordinates given in a previous structure analysis, "Crystal Structure and Absolute Configurati on of Qinghaosu," Qinghaosu Research Group, Institute of Biophysics, Academ ica Sinica, Scientia Sinica, Vol. XXIII No. 3, 380 (1980), do not display t he molecule in its absolute configuration.].