Chemists have found that the seeds of the sweetgum fruit contain significant amounts of shikimic acid, the starting material used to produce the main antiviral agent in a much-heralded drug for fighting bird flu. Their findings, which could help increase the global supply of the drug, were described today at the 231st national meeting of the American Chemical Society, the world’s largest scientific society.
Shikimic acid is used to make a generic drug called oseltamivir — best known commercially as Tamiflu® — which is used to fight many types of flu viruses. Some health experts believe that this and similar antiviral drugs could help save lives by slowing the spread of the virus in the absence of a bird flu vaccine, which is still in development.
The drug, which blocks the replication of the flu virus, is being stockpiled worldwide to slow or stop a possible bird flu pandemic that some experts predict could kill millions — if the virus mutates into a form that can spread from person to person. The virus, a strain known as H5N1, primarily afflicts birds at present but has been known to kill a small but growing number of humans who have had close contact with infected birds.
There is a skyrocketing demand for Tamiflu, but some experts fear there won’t be enough of the drug to treat everyone if a worldwide pandemic occurs. The supply problem resides in the drug’s source: The shikimic acid used to make it is obtained almost exclusively from the Chinese star anise, a fruit that is found mainly in China and whose supply has dwindled due to high demand for the flu drug. Although shikimic acid is found in many plants, star anise has been considered the most abundant plant source, until now.
"Our work gives the hearty sweetgum tree another purpose, one that may help to alleviate the worldwide shortage of shikimic acid," says study leader Thomas Poon, Ph.D., a professor of chemistry from the W.M. Keck Science Center at The Claremont Colleges in Claremont, Calif. "They have lots of potential for fighting bird flu."
The sweetgum tree grows widely throughout the United States and other parts of the world. In this country, it is particularly common in the South, including the Carolinas, Georgia and Alabama, but also can be found as far west as Missouri, Arkansas and Oklahoma and northward in parts of Illinois.
Although shikimic acid is found in the leaves and bark of the tree, it is most abundant in the fruit, Poon says. In the mature tree, the fruit emerges as a green seedpod that later dries into a brown, spiny husk, which releases an abundance of tiny, grain-like seeds. To optimize shikimic acid extraction, the gumballs need to be harvested when they are still green and before the seeds have been dispersed, Poon says. Each tree can hold hundreds, if not thousands, of seedpods.