In developing evidence for a 20-year-old hypothesis about a toxin found in red tide, MIT chemists have worked out techniques that could also streamline the production of certain drugs.
Associate professor Tim Jamison devised a simple method for producing brevetoxin, a compound made by the microörganisms that cause red tides along the world’s coastlines. Scientists can’t predict the occurrence of these algal blooms, which poison marine animals and those who eat them; nor can they explain why they happen. And they have previously been able to synthesize the toxins only in small quantities, although algae produce them in abundance. But Jamison and his colleagues have provided strong support for the Nakanishi hypothesis, which outlines how the organisms might produce the compounds that make them so dangerous.
Jamison says he was “fascinated by the natural structure” of brevetoxin and drawn to the simplicity of the unproven hypothesis. It proposes that compounds like brevetoxin, which consist of ladders of carbon rings, are made in a cascade that begins when one ring is opened at a particular spot to allow the next ring to attach. But breaking the ring at the right place takes a lot of energy, so scientists have had trouble duplicating the reaction.
Others hoping to synthesize brevetoxin have tried to make the ring easier to open by adding atoms to one of the starting compounds, an epoxide group, at the crucial spot. “But this is clearly not what nature does,” says Jamison. He and his colleagues nudge the reaction forward with a template that resembles part of the structure of the brevetoxin they want to produce. “First we construct one of the rings found in the natural [end] product,” Jamison says. Then they attach a chain of epoxides. “This makes the formation of the next ring more favorable.”
Reactions like the synthesis of brevetoxin are normally carried out in oily solvents like dichloromethane or toluene. “Organic chemists tend to avoid water,” Jamison says. “It’s the old adage: oil and water don’t mix.” But Jamison and his colleagues noticed that the reactions worked better when the solvents were contaminated with small amounts of water. Entirely replacing the solvents with water made the reactions work better still.
Algae may not make ladder toxins the way the MIT group did. Still, Jamison guesses that the ring template might mimic enzymes that help cells make brevetoxin and other compounds in the presence of water.
He’s now applying the water-based technique to other biological reactions, including the synthesis of steroids. He’s also using it to try to make brevenal, a compound that shows promise as a therapy for cystic fibrosis but is costly to make. “If one could promote a reaction using just water, that’d be tough to beat economically–especially if it works better,” he says.
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