A novel (5E,9Z)-dialkylindolizidine from the ant Monomorium smithii.

The alkaloidal venom of Monomorium smithii was found to contain (5E,9Z)-3-butyl-5-(4-penten-1-yl)indolizidine [1b], a novel indolizidine, its monocyclic analogue trans-2-butyl-5-(8-nonen-1-yl)pyrrolidine [2], (5E,8Z)-3,5-di(5-hexen-1-yl)pyrrolizidine [3], and trans-2-(5-hexen-1-yl)-5-(8-nonen-1-yl)pyrrolidine [4]. The structure of 1b was based on the results of two independent syntheses. Reductive amination of the appropriate triketone confirmed the carbon-nitrogen skeleton of 1b and suggested its stereochemistry, which was verified by the results of a stereoselective synthesis based on pyrrole hydrogenation. The chemotaxonomic implications of this first report of the concomitance of a 3,5-dialkylindolizidine and a 3,5-dialkylpyrrolizidine in an ant venom are discussed.