A MAS-NMR study of the location of (+)-totarol, a diterpenoid bioactive molecule, in phospholipid model membranes.

(+)-Totarol, a diterpenoid isolated from Podocarpus spp., is a potent antioxidant and antibacterial agent. Although the mechanism of action of this hydrophobic molecule is poorly understood, recent work from our laboratories suggests that it could be due to membranotropic interactions. The location of (+)-totarol in membranes and its interaction with membrane components is therefore of considerable interest. High resolution magic angle spinning (MAS) natural abundance 13C nuclear magnetic resonance studies were undertaken to assess the location of (+)-totarol in model membranes composed of egg yolk phosphatidylcholine (EYL). 13C spin-lattice relaxation times (T(1)) of both the phospholipid and (+)-totarol molecules in the presence of Gd(3+) were measured to obtain information on molecular distances. Our results indicate that (+)-totarol is situated in the upper region of the membrane, with its hydroxyl group located in the vicinity of the C-3/4 carbon atoms of the phospholipid acyl chain, and nearly perpendicular with respect to the phospholipid acyl chain axis. Such a location of (+)-totarol in the membrane would be expected to compromise the functional integrity of the membrane and account, at least in part, for its antibacterial effects.