Occurrence and significance of decahydroquinolines from dendrobatid poisonfrogs and a myrmicine ant: Use of H-1 and C-13 NMR in their conformationalanalysis

Structures for 2,5-disubstituted decahydroquinolines (DHQs) are reported fo r the two diastereomeric pairs cis-275B (14) and cis-275B' (15) and 5-epi-t rans-269AB (18) and trans-269AB (19), all isolated from skin extracts of de ndrobatid frogs, and for 5-epi-cis-275B' (16) and 5-epi-trans-275B (17) fou nd in the extracts of virgin queens of a myrmicine ant [Solenopsis (Diplorh optrum) azteca]. Detection of such DHQs in an ant, their first reported occ urrence, strengthens a dietary hypothesis for the origin of the approximate ly 30 DHQs that have been detected in extracts of frog skin. NMR data on th e two conformers of cis-decahydroquinoline permit assignment of ring confor mations and stereochemistry to cis-DHQs of the "N-endo" type or the "N-exo" type. These conformations are also assigned on whether H-8a is equatorial or axial as determined with E-COSY or 1D-HOHAHA spectra.