The US Court of Appeals for the Federal Circuit affirmed a lower court ruling that a claim must at a minimum include the recited enantiomer. Sumitomo Dainippon Pharma Co., Ltd. v. Emcure Pharmaceuticals Ltd., et al., Case No. 887 F.3d 1153 (Fed. Cir., Apr. 16, 2018) (Stoll, J). 

The case arose under the Hatch-Waxman Act and involved a patent covering lurasidone, the active ingredient in the schizophrenia and bipolar depression drug LATUDA. Appellants sought approval to market generic versions of LATUDA. Plaintiffs initiated the lawsuit and asserted claim 14 of the patent, which recites an imide compound of a particular formula or an acid additional salt thereof.

The parties agreed that the specific formula depicted in the claim is lurasidone, a (-) enantiomer. Enantiomers can be of the (-) or (+) type, and a mixture with 50 percent of each of the (-) and (+) enantiomer is known as a racemate or racemic mixture. Appellants sought to limit claim 14 to “racemic mixture of two enantiomers of which the structural formula is representative.” The district court rejected appellants’ construction, explaining that such a construction would exclude the (-) enantiomer depicted in claim 14. Thereafter, the district court construed the claim as covering “lurasidone, lurasidone’s enantiomer as well as mixtures of these enantiomers.” Appellants appealed.

On appeal, the Federal Circuit affirmed the district’s court finding that the claim covered at a minimum the (-) enantiomer. The Federal Circuit, however, declined to address the rest of the lower court’s construction, explaining that appellants had conceded infringement under such a construction.

The Federal Circuit began its analysis by examining the claim language. The Court noted that appellants did not dispute that a skilled artisan “looking at claim 14’s structure in a vacuum would understand it to be one way of depicting the (-) enantiomer.” By contrast, nothing in the claim language limited the claim scope to a racemate, the Court explained. 

Turning next to the patent specification, the Court noted that the specification describes the enantiomer as a preferred embodiment and does not disclaim the (-) enantiomer. The specification does not disparage the (-) enantiomer, nor does it refer to the racemic mixture as forming the basis for the invention or all the patent’s embodiments. As for appellants’ argument that the claimed structure was the same as compound 101, which appellants contended was a racemate, the Court disagreed that compound 101 was a racemic mixture and further concluded that the specification does not define claim 14’s structure as compound 101.

The Court also did not find appellants’ extrinsic evidence in the form of textbooks and expert testimony compelling. Noting that extrinsic evidence is in general “less significant than intrinsic evidence,” the Court explained that even though the appellants’ expert had argued that it was conventional in the art to use a single enantiomer to depict a racemate, the expert did not state that a person of ordinary skill in the art would understand a “depiction of a single enantiomer to exclude the very enantiomer depicted.”

Practice Note: A claim construction that excludes the recited structure is likely to be rejected.