Pyridine alkaloids in the venom of imported fire ants

Authors: Chen, Jian; WANG, LIKUN - Zhejiang University; ZHAO, JIN-HAO - Zhejiang University

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/20/2019
Publication Date: 10/16/2019
Citation: Chen, J., Wang, L., Zhao, J. 2019. Pyridine alkaloids in the venom of imported fire ants. Journal of Agricultural and Food Chemistry. 41:11388-11395.

Interpretive Summary: In the past two decades, solid-phase microextraction (SPME) has been getting more and more popular in chemical analysis. In SPME, analytes in the sample are adsorbed/absorbed onto a fiber that is coated with a liquid or solid extracting phase. The fiber is then transferred to the injection port of separation instruments, such as gas chromatography–mass spectrometry (GC-MS). In SPME-GC-MS, thermal desorption of the analytes takes place in the inject port. Although the type of extracting phase may determine what analytes can be preferentially extracted from the sample, the separation is mainly achieved by chromatography. In this study, we studied the venom alkaloids of imported fire ants using SPME-GC-MS. We demonstrated that the thermal desorption process can be manipulated to facilitate the separation and identification of analytes that co-eluted with interfered compounds if the target analyte was slower to be desorbed. Using this approach, ten 2-methyl-6-alkyl (or alkenyl)pyridines were found the first time from the venom of imported fire ants, which opens a new research avenue on the toxicological and pheromonal property of fire ant venom. This innovation may significantly extend the application of SPME in chemical analysis.

Technical Abstract: Due to its simplicity and solvent free extraction capability, solid phase microextraction (SPME) has gained its wide popularity in the field of analytical chemistry. In SPME, analytes are adsorbed /absorbed onto a fiber that is coated with a liquid or solid extracting phase. The fiber is then transferred to the injection port of separation instruments, such as gas chromatography coupled with mass spectrometry (GC-MS). In SPME-GC-MS, thermal desorption of the analytes takes place in the inject port. Although the type of extracting phase may determine what analytes can be preferentially extracted from the sample, the separation is mainly achieved by chromatography. In this study, we studied the venom alkaloids of the red imported fire ant, Solenopsis invicta Buren, the black imported fire ant, Solenopsis richteri Forel, and the hybrid, S. invicta × S. richteri, using SPME-GC-MS. All these ants are serious pests to the public health, agriculture and ecosystems. We demonstrated that the thermal desorption process can be manipulated to facilitate the isolation and identification of analytes that co-eluted with interfered compounds if the target analyte was slower to be desorbed. After SPME extraction of ant venom, we conducted a series of consecutive GC-MS injections, each with a partial desorption. Several hidden peaks were revealed after the interfered analytes with larger GC peaks had been desorbed. Using this method, ten 2-methyl-6-alkyl (or alkenyl)pyridines were found the first time from the venom of imported fire ants. Structures of three pyridine alkaloids were confirmed by synthesis, including 2-methyl-6-undecylpyridine, 2-methyl-6-tridecylpyridine, and 2-methyl-6-pentadecylpyridine.