Around 170 species of poison arrow
frogs exist in the rainforests of South America, from
which 400 toxins have been extracted and classified
today. The frogs range from bright blue to startling
yellow in colour, and one species has shot to scientific
prominence since the isolation of its skin toxin 1974.
The tiny red frog smaller than a fingernail may provide
an invaluable implement in the modern medical toolkit
in coming years.
What's in a frog?
Equadorian poison arrow frog
chemical name (chloropyridyl)-azabicycloheptane,
is a toxin derived from the skin of the equadorian
poison tree frog, Epipedobates
Tricolor, and named in the
honour of the frog. The frogs are red and green
stripped, and the toxin they produce was used
by the frogs themselves against predators, and
also by native Indians to tip their arrows. The
frogs were so toxic, arrow tips only had to be
rubbed across the back of a frog to coat them
The poison's toxicity causes paralysis
even in the minute doses secreted by the frog
and a dose of just 2 miligram can kill a person.
Biosynthesis of Epibatidine does
not occur in the frog, and amazingly, the frogs
are not affected by the poison. Over millions
of years, the frogs have evolved to become resistant
and use it to their advantage.
Why is epibatidine so important?
Other than for coating the arrowheads of natives and
causing their enemies to suffer a convulsive,
paralysed, albeit painless death, it was discovered
that the toxin also held potent analgesic (painkilling)
effects, surpassing even opioids such as morphine.
Most painkillers operate via the same
pathway as morphine, and act on opioid receptors,
whereas epibatidine has a similar structure to
nicotine, and compete
with nicotine receptors. This sparked interest,
and research followed to derive non-toxic compounds
with the same effect. Current research is concentrating
on ABT-594, a promising analogue.
Epibatidine is a alkaloid (nitrogen
containing compound) consisting of 2 ring structures.
The compound is displayed on the right.
For more on synthetic routes
for epibatidine and derivatives, click