Structure of alkaloid 275A, a novel 1-azabicyclo[5.3.0]decane from a dendrobatid frog, Dendrobates lehmanni: Synthesis of the tetrahydrodiastereomers

The principal alkaloid 275A in skins of the Colombian poison frog Dendrobat es lehmanni has been identified as the pyrrolo[1,2-alpha ]azepane (1), the first occurrence in nature of this "izidine" system. Tetrahydro-l proved id entical to one of the four synthetic diastereomers, 2a-2d, thereby establis hing that 1 has the 5Z,10E relative stereochemistry. Alkaloid 1 is often ac companied by other congeners, in particular a 5Z,10Z diastereomer 15, a dih ydro analogue 16, and a ketone 17. Such izidines in frogs may arise from di etary ants, as do other classes of izidines.