Detection of a new piperideine alkaloid in the pygidial glands of some Stenus beetles.

Rove beetles of the genus Stenus produce and store bioactive alkaloids like stenusine (3), 3-(2-methylbut-1-enyl)pyridine (4), and cicindeloine (5) in their pygidial glands to protect themselves from predation and microorganismic infestation. The biosynthesis of stenusine (3), 3-(2-methylbut-1-enyl)pyridine (4), and cicindeloine (5) was previously investigated in Stenus bimaculatus, Stenus similis, and Stenus solutus, respectively. The piperideine alkaloid cicindeloine (5) occurs also as a major compound in the pygidial gland secretion of Stenus cicindeloides. The three metabolites follow the same biosynthetic pathway, where the N-heterocyclic ring is derived from L-lysine and the side chain from L-isoleucine. The different alkaloids are finally obtained by few modifications of shared precursor molecules, such as 2,3,4,5-tetrahydro-5-(2-methylbutylidene)pyridine (1). This piperideine alkaloid was synthesized and detected by GC/MS and GC at a chiral phase in the pygidial glands of Stenus similis, Stenus tarsalis, and Stenus cicindeloides.