A simple sweet from an Aztec herb.

In the 1570s, Spanish physician Francisco Hernandez described a remarkably sweet plant known to the Aztecs as Tzonpelic xihuitl or "sweet herb." This reference, accompanied by an accurate description and illustration of the plant, now has led pharmacologists to a previously unrecognized, intensely sweet chemical that they expect to be useful in their modern mission -- creating new substances that satisfy the sweet tooth without causing tooth decay.

A. Douglas Kinghorn, graduate student Cesar M. Compadre and collaborators at the University of Illinois Medical Center in Chicago isolated the newly identified sweet compound from leaves and flowers of plants, now called Lippia dulcis Trev., collected in central Mexico. The researchers determined the chemical structure of the pure, colorless oil, which they have named hernandulcin after the 16th century physician. By subtly modifying the structure, they identified two chemical groups that are essential for the sweet taste -- the carbon-oxygen (carbonyl) group at carbon 1 and the hydrogen-oxygen (hydroxyl) group on carbon 1'.

"This is a very simple structure," Kinghorn says. "It should be useful in studies on the relationship between chemical structure and sweetness, and in the rational design of sweeteners."

The purified compound will not go directly into the sugar bowl, however. Although a panel of 17 trained volunteers found hernandulcin to be more than a thousand times sweeter than sucrose, it has some taste drawbacks. It was considered to be "somewhat less pleasant than sucrose and to exhibit perceptible off- and after-tastes as well as some bitterness," the scientists report in the Jan. 25 SCIENCE.

But hernandulcin continues to show promise in its health effects. It did not cause bacterial mutations in the standard test for indications of cancer-causing potential, and, even at a high dose, it did not harm mice. Further tests have indicated that the chemical should not cause dental cavities, Kinghorn says.

The scientists plan to modify hernandulcin in the hope of making it more palatable. They have filed a patent application on the sweetener and are currently negotiating with a food company.