After 100 years of trying, scientists have found a way to create the pufferfish neurotoxin

Tetrodotoxin (TTX) is the most poisonous natural neurotoxin known to humanity. It is produced in the body of marine animals like pufferfish, snails, octopuses, newts, frogs, and worms. To study and harness the power of this mysterious biochemical, scientists in different parts of the world have been trying to synthesize TTX in lab settings for over a hundred years. It looks like a New York University (NYU) team has figured it out.

In a recently published study, the researchers have revealed a 22-step process using which biologically active, highly efficient tetrodotoxin (and its derivatives) can be created from commercially available materials. They claim to have discovered the most “concise” TTX synthesis method. One of the study's authors and Janice Cutler Professor of Chemistry at NYU, Dirk Trauner told IE, “Our synthesis is not the first synthesis of tetrodotoxin; however, it is the most efficient to date, improving on state of the art by 30 fold.” 

Why is the synthesis of TTX a big achievement? 

Tetrodotoxin is often referred to as an enigma by many scientists because they are still unsure how animals like pufferfish produce and store this poisonous substance in their bodies. Moreover, a great mystery surrounds the chemical’s properties being used for purposes other than self-defense. Professor Trauner and his team believe that TTX can be considered a “keystone molecule” because of the role it could play in defining the predator-prey relationship in our ecosystem. 

Plus, it is also believed to function as a pheromone or as a feeding stimulant in some organisms. As a potent paralytic neurotoxin, TTX can block sodium conductive ion channels in nerve cell membranes and silence signals within neural circuits. This brings us to the biggest reason why scientists have been fascinated with tetrodotoxin for so long. 

The researchers claim that the sodium channel blocking ability of TTX holds secrets related to developing a new class of effective painkillers. “There is an enormous medical need for painkillers with new modes of action, particularly ones that work differently from opioids. Tetrodotoxin has the interesting property of blocking nerve signals. These nerve signals are integral to the sensation of pain, and due to this, tetrodotoxin is thought to be a promising lead for the development of non-addictive, next-generation pain killers,” said Trauner.

Why did lab synthesis of TTX take so much time?

Tetrodotoxin is found in marine animals' liver and reproductive organs, such as toads, newts, and pufferfish. Japanese scientist Dr. Yoshizumi Tahara isolated TTX for the first time in 1894 and confirmed the same in 1909. Since then scientists have been studying and trying to synthesize the chemical in laboratory settings. 

However, creating a stable and pure version of tetrodotoxin has been challenging for biochemists because of its highly complex structure and chemical instability. Although scientists have been able to synthesize TTX in the past as well, most of those neurotoxins were either highly unstable or less efficient. 

Plus, many of those methods weren’t scalable as they involved numerous steps with their complications. “The main challenge in the synthesis of tetrodotoxin is its high-degree chemical complexity, chemical instability, and the challenge posed in its purification and isolation. This is reflected in the previous synthesis which required more steps and were less efficient overall,” Professor Trauner told IE.

Interestingly, the TTX synthesis approach suggested by NYU researchers starts with a glucose derivative, involves only 22 steps, and delivers an impressive 11% yield. Professor Trauner and his team claim that their approach is currently the most efficient and probably the only scalable method suited for producing tetrodotoxin and its derivatives. The researcher will now use their platform to further study the neurotoxin's analgesic properties. 

The study is published in the journal Science.

Abstract:

Tetrodotoxin (TTX) is a neurotoxic natural product that is an indispensable probe in neuroscience, a biosynthetic and ecological enigma, and a celebrated target of synthetic chemistry. Here, we present a stereoselective synthesis of TTX that proceeds in 22 steps from a glucose derivative. The central cyclohexane ring of TTX and its a-tertiary amine moiety were established by the intramolecular 1,3-dipolar cycloaddition of a nitrile oxide, followed by alkynyl addition to the resultant isoxazoline. A ruthenium-catalyzed hydroxylactonization set the stage for the formation of the dioxa-adamantane core. Installation of the guanidine, oxidation of a primary alcohol, and a late-stage epimerization gave a mixture of TTX and anhydro-TTX. This synthetic approach could give ready access to biologically active derivatives.