The isolation and structure of the novel cis-fused indolizidine 249H from frog skin: cis- vs. trans-fused indolizidines distinguished by NMR

A 5,6,8-trisubstituted indolizidine structure (1) is proposed for alkaloid 249H isolated from dendrobatid frogs based upon NMR and IR spectroscopy and MS spectrometry. It has an unusual (E)-3-hexen-3-yl side-chain, the first branched substituent reported among the simple indolizidines from frog skin , an unusual cis-fused indolizidine ring and finally an atypical E configur ation of H-5 relative to H-9.