Synthesis of Isotopically Labelled Disparlure Enantiomers and Application to the Study of Enantiomer Discrimination in Gypsy Moth Pheromone‐Binding Proteins

To study the binding mechanism of disparlure (7,8)-epoxy-2-methyloctadecane enantiomers with pheromone-binding proteins (PBPs) of the gypsy moth, oxygen-17 or 18 and 5,5,6,6-deuterium labelled disparlure enantiomers were prepared in an efficient, enantioselective route. Key steps involve the asymmetric α-chlorination of dodecanal by SOMO catalysis and Mitsunobu inversion of a 1, 2-chlorohydrin. The pheromone, (+)-disparlure (7R, 8S), was tested in two infested zones, demonstrating that it is very attractive towards male gypsy moths. Studies of the binding of (+)-disparlure and its antipode to gypsy moth PBPs by 2H &17O NMR at 600 MHz are reported. Chemical shifts, spin-lattice relaxation times and transverse relaxation times of deuterium atoms of disparlure enantiomers in 2H NMR show that binding of disparlure enantiomers to PBP1 differs from binding to PBP2, as expected from their opposite binding preferences (PBP1 binds (-)-disparlure, and PBP2 binds (+)-disparlure more strongly). Models of the disparlure enantiomers bound to one internal binding site and two external binding sites of both PBPs were constructed. The observed chemical shift changes of deuterated ligand signals, from non-bound to bound, T1 and T2 values are correlated with results from the simulations. Together these results suggest that the disparlure enantiomers adopt distinct conformations within the binding sites of the two PBPs and interact with residues that line the sites.