A General and Efficient Approach to the Proposed Structures of Frog Toxins: The 5-Alkylindolizidines

The structural assignments of a number of bicyclic alkaloids isolated from frogs have been reassigned or questioned after synthesis of the proposed structures. Herein we report a practical and short formal synthesis of the 5-alkylindolizidine core, from readily available α-amino acids or homoserine that could be utilized to support structural assignments.