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The Holton Process

What brought Taxol into the marketplace and possibly saved the extinction of the Pacific yew tree—until 1990 the only source for it—was this ingenious lab process developed by a team of FSU synthetic organic chemists led by Robert Holton.

The process starts with the large molecule 10-Deacetylbaccatin III (or 10-DAB), a natural compound found in abundance in the needles of the English yew, a common European shrub. 10-DAB is the “heart” of the Taxol molecule, which has a distinctive appendage known as an ester side-chain. Until Holton's breakthrough, attaching this side-chain of just 34 atoms to the 10-DAB mother molecule in the lab had never been practical.

Holton's team first found a way to bind the ester side-chain so that it would be small enough to enter a particular cavity within the convoluted body of the 10-DAB molecule where it could attach to a key site, known as the C-13 hydroxyl group, shown here as “OH.”

The team subsequently discovered a way to greatly speed up the process and make it far more efficient by treating the combination process with a metal alkoxide catalyst. This MAP (metal alkoxide process) catapulted Taxol into the world's best-selling anti-cancer drug by 1994, generating world-wide sales approaching $10 billion by 2000.

Out of the Park
Holton Process
Beyond Taxolog