New alkaloids from ants: Identification and synthesis of (3R,5S,9R)‐3‐butyl‐5‐(1‐oxopropyl)indolizidine and (3R,5R,9R)‐3‐butyl‐5‐(1‐oxopropyl)indolizidine, constituents of the poison gland secretion in Myrmicaria eumenoides (hymenoptera, formicidae)

The (3R,5S,9R) and (3R,5R,9R) stereoisomers of 3‐butyl‐5‐(1‐oxopropyl)indolizidine (9) were identified as major constituents of the poison gland secretion of the African ant, Myrmicaria eumenoides. Racemates of the four diastereomers of 9 were synthesized via the corresponding ethyl 5‐(5‐butylpyrrolidin‐2‐yl)pentanoates (6). Enantiomerically pure samples of the (3R)‐stereoisomers of 9 were obtained by starting from (2R)‐2,3‐O‐isopropylideneglyceric aldehyde (21) and 6‐methylpyridine‐2‐carboxaldehyde (20). In addition, the enantiomeric separation by chiral gas chromatography and unambiguous structure assignment of the target compounds are described.