KATTEN MUCHIN ROSENMAN LLP
Enantiomer Patents: Innovative or Obvious?
Reproduced with permission from the Pharmaceutical Law & Industry Report, 12 PLIR 184, (February 7, 2014).
Copyright 2014 The Bureau of National Affairs, Inc. (800-372-1033) www.bna.com.
– By Brian Sodikoff, Christopher B. Ferenc and Patrick Abbott
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.
II. Scientific Background: A Primer for Non-Scientists
A molecule is a group of atoms held together by covalent bonds. Different molecules have different physical and
chemical properties depending on their constituent atoms, the strength of the bonds between them, and their spatial
arrangement. For instance, drinking pure water (H2O) will keep you alive, drinking pure hydrogen peroxide (H2O2) could
kill you, and drinking pure alcohol (C2H5OH) will do something else altogether.
Molecules that have the exact same formula, but different spatial arrangements, are known as isomers. For example,
butane (C4H10) has two constitutional isomers: n-butane, where the four carbons are linked in a single chain, and
isobutane, where three carbons are each linked to a central carbon.
