Structure of Alkaloid 275A, a Novel 1-Azabicyclo[5.3.0]decane from a Dendrobatid Frog, Dendrobates lehmanni: Synthesis of the Tetrahydrodiastereomers
摘要:
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.
Hydroformylation of terminal alkenes in alcohol solvents leads to the selective formation of the corresponding acetals. The Xantphos ligand gave the best results as well as acetal selectivities higher than 99% and linear/branched ratios of up to 52 were obtained. The scope of the reaction was studied. Acetals were found to be unreactive under hydroaminomethylation conditions.