CRYSTAL-STRUCTURE AND ABSOLUTE-CONFIGURATION OF THE INDOLE ALKALOID ARBORESCIDINE-C

The structure and absolute configuration (3R, 17R) of the indole alkal oid arborescidine C were determined by x-ray diffraction. The six-memb ered ring assumes a half-chair conformation and the seven-membered rin g has a twist-like conformation. The crystal packing is characterized by intermolecular hydrogen-bonding between the hydroxyl group and nitr ogen atom N4 which leads to the formation of infinite chains of molecu les along the a-axis of the crystal. The absolute configurations of tw o related indole alkaloids, arborescidine B and arborescidine D are in ferred from the experimentally determined configuration of arborescidi n C molecule. A comparison of the present structure with that of a rel ated indole alkaloid akagerine showed significant conformational and c onfigurational differences. Crystal data: C16H19N2OBr, orthorhombic, P 2(1)2(1)2, a = 10.3376(8), b = 15.461(4), c = 9.2094(9)Angstrom, V = 1 471.9(6)Angstrom(3), Z = 4, D-calc = 1.510 g cm(-3), lambda = 1.54178 Angstrom.