Histrionicotoxins: Roentgen-Ray Analysis of the Novel Allenic and Acetylenic Spiroalkaloids Isolated from a Colombian Frog, Dendrobates histrionicus

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Abstract
The structures and absolute configuration of two unique alkaloids isolated from the Colombian frog, Dendrobates histrionicus , have been elucidated by Roentgen-ray (x-ray) crystallography. Histrionicotoxin is (2 p R, 6S, 7 p S, 8 a S)-7-( cis -1-buten-3-ynyl)-8-hydroxy-2-( cis -2-penten-4- ynyl)-1-azaspiro[5.5] undecane, while in dihydro-isohistrionicotoxin the acetylenic 2-pentenynyl side chain is replaced by an allenic 2-(3,4 pentadienyl) substituent. Dendrobates histrionicus exhibits remarkable interpopulational variations in amounts and composition of skin toxins, in behavior, and in phenotypic characters, aspects of which are illustrated in a color plate. The histrionico-toxins are the third class of alkaloids isolated from the defensive skin secretions of Neotropical (Dendrobatidae) frogs.