CRYSTAL AND MOLECULAR PACKING OF SIX RYANIA ALKALOIDS: THE PREDOMINANCE OF A MULTI-DIMENSIONAL H-BOND NETWORK. Marc Drouin, Marco Dodier and Luc Ruest. Département de Chimie, Université de Sherbrooke, Sherbrooke, Québec, Canada, J1K 2R1.

Originally extracted from Ryania speciosa Vahl plant, the natural insecticide ryanodine is also a calcium release channel modulator in mammalian muscle. In order to identify structural features which are necessary to keep biological activity, several polyhydroxylated diterpene compounds were isolated from the plant or synthesized upon testing their biological activity. Their respective crystal structures were elucidated to confirm their stereochemistry and exact molecular structure. The general aspect of the molecules show a highly polar face with many OH groups opposite to a relatively hydrophobic face. The molecular packing are dominated by a two- or a three-dimensional hydrogen bonding network with many intra- and intermolecular hydrogen bonds. Elaborate crystal packing are presented, highlighting minor changes in molecular structures inducing major differences in H-bond network systems. As example, the cinnzeylanol compound (R1=OH, R2=H) display a highly disordered water channel whereas 2-deoxy 3-epiryanodol (R1=H, R2=OH) contains no solvent molecules.