Enantiomer Patents: Innovative or Obvious?

Katten Muchin Rosenman LLP

I. Introduction -

Stereochemistry relates to the spatial organization of atoms in a molecule. Often molecules having the same chemical makeup can exist in different spatial arrangements. These related molecules are known as stereoisomers. While stereoisomers have been studied since the 19th century, their impact on the safety and efficacy of pharmaceutical compounds was not readily appreciated until the 1970s. In fact, until a series of public health catastrophes forced the issue, isolating and administering a single stereoisomer was not a focus of research. Of particular interest were enantiomers. Enantiomers are a subset of stereoisomers, wherein two molecules exist as mirror images of each other, much like our right and left hands. As the potential benefits of administering a single enantiomer over a mixture of enantiomers were more understood, their popularity in the pharmaceutical industry grew. Today, enantiomeric drugs, constitute a significant portion of the prescription medications available to consumers, and are the active ingredients in such major brands as Lipitor, Plavix, Nexium, Azilect, and Nuvigil.

As the market value of enantiomeric drugs has grown, so too has the focus on the patents protecting them. In recent years, the validity of several patents claiming a single enantiomer have been challenged in the courts. Generally, the most germane issue in these cases turns on whether the claimed invention is an obvious variant of what previously existed. When assessing the obviousness of a patent claim, courts focus on four factors: (1) the scope and content of the prior art; (2) the level of ordinary skill in the pertinent art; (3) the differences between the claimed subject matter and the prior art; and (4) objective evidence such as commercial success, long-felt need, and the failure of others. Graham v. John Deere Co., 383 U.S. 1, 17-18 (1966). These factors are considered in order to determine whether a particular advance in technology is true innovation or the result of the normal progress, which is not subject to exclusive rights under the patent laws. KSR Int’l Co. v. Teleflex Inc., 127 S. Ct. 1727, 1746 (2007). In this article, we navigate recent obviousness challenges of enantiomer patents to determine how courts have applied these complex factual analyses in practice. Because these cases necessarily turn on intricate factual issues, the brief scientific primer below provides some context for the later legal discussion.

Originally published in the Pharmaceutical Law & Industry Report, 12 PLIR 184, (February 7, 2014).

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