CAMBRIDGE, Mass. ( TheStreet) -- GlaxoSmithKline ( GSK) has cracked down on two of its U.S. executives for selling the anti-aging supplement resveratrol without the company's knowledge or permission, and by doing so, conceivably undermining Glaxo's nearly $1 billion investment in resveratrol drug research. The U.K.-based pharmaceutical giant ordered Cristoph Westphal and Michelle Dipp Thursday to cease selling a resveratrol dietary supplement through a nonprofit venture known as the Healthy Lifespan Institute that the two executives helped establish last year, TheStreet has learned. Westphal and Dipp were both principal executives at Sirtris Pharmaceuticals when Glaxo acquired the company in 2008 for $720 million. Glaxo bought Sirtris for its expertise in developing drugs based on resveratrol, a chemical found in red wine which some research suggests may ramp up the metabolic activity in cells and could one day be used to treat diabetes, cancer and many other diseases. Westphal and Dipp joined Glaxo after the Sirtris acquisition and continued to direct Glaxo's continuing efforts into resveratrol drug development. Unbeknownst to Glaxo, the two executives were also moonlighting as purveyors of their own custom-made dietary formulation of resveratrol. The resveratrol sold by Westphal and Dipp is formulated differently and is less potent than Glaxo's resveratrol drugs, according to the company. Consumers could purchase resveratrol online from the Healthy LifeSpan Institute run by Westphal and Dipp at a cost of $540 for a one-year supply. The web site Xconomy first reported on Westphal and Dipp's extra-curricular activities Thursday. Westphal and Dipp informed Glaxo about the formation of the Healthy Lifespan Institute, but "GSK Glaxo was not aware that the Healthy Lifespan Institute was selling a resveratrol formulation on the Internet. The company has instructed the GSK employees to cease their association with this activity and Michelle Dipp and Christoph Westphal will be resigning their positions on the board of Healthy Lifespan," said Glaxo spokeswoman Sarah Alspach in a statement emailed to TheStreet. Westphal, who is also a partner in a venture capital firm based in Boston, would not answer questions, according to his spokeswoman. Dipp could not be reached. Resveratrol is a natural compound and can therefore be sold via retail channels as a dietary supplement without regulatory approval. Glaxo, however, spent $720 million to acquire Sirtris with the hope that a prescription drug made from resveratrol would one day be approved by U.S. or European regulators with a specific medical claim to treat or cure a disease like diabetes or cancer.