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 Dendrobates lehmanni has been identified as the pyrrolo[1,2-alpha ]azepane (1), the first occurrence in nature of this izidine system. Tetrahydro-l proved identical to one of the four synthetic diastereomers, 2a-2d, thereby establishing that 1 has the 5Z,10E relative stereochemistry. Alkaloid 1 is often accompanied by other congeners, in particular a 5Z,10Z diastereomer 15, a dihydro analogue 16, and a ketone 17. Such izidines in frogs may arise from dietary ants, as do other classes of izidines.