2-Ethyl-3,6-dimethylpyrazine (EDMP) was an alarm pheromone component isolated from\nthe mandibular gland of the red imported fire ant, Solenopsis invicta Buren. Several pyrazine analogues\nhave been previously found to elicit significant alarm responses in S. invicta workers. This study\naimed to separate the commercially available 2-ethyl-5(6)-methylpyrazine (EMP), i.e., a mixture of\n2-ethyl-6-methylpyrazine (2E6MP) and 2-ethyl-5-methylpyrazine (2E5MP), and to examine both\nelectroantennogram (EAG) and behavioral responses of S. invicta workers to EMP and the purified\nisomers. HPLC separations were achieved using a polysaccharide chiral stationary phase (Chiralpak\nAD-H) column with both mobile phases: Cyclohexane/isopropanol, and hexane/isopropanol. A ratio\nof 99:1 was selected for the separation of EMP at semipreparative level. The structures of the\nisomers obtained through the cyclohexane/isopropanol mobile phase were confirmed by detailed\nanalyses of 2D-HSQC- and -HMBC-NMR data. The two isomers showed differential methine Cââ?¬â??H\ncorrelations evidenced by 2D-HMBC-NMR spectra. The two concentrated fractions obtained through\nhexane/isopropanol mobile phase were subjected to EAG test and behavioral bioassay on S. invicta\nworkers. The two HPLCâË?â??purified isomers, 2E6MP and 2E5MP, and their mixture (1:1) at same\ndose elicited similar EAG and alarm responses, indicating that these two isomers are equally active.\nThe 2D-NMRâË?â??spectroscopic characterization, and electrophysiological and alarm activities of 2E6MP\nand 2E5MP were reported here for the first time.
Loading....