Claim Construction Of An Enantiomeric Chemical Structure
In Sumitomo Dainippon Pharma Co. V. Emcure Pharm. Ltd., the Federal Circuit affirmed the district court’s decision that construed a chemical structure as reading on the lurasidone enantiomer that is the active ingredient of Latuda®. While the decision was in favor of the patentee, the required analysis suggests that applicants may want to consider using other nomenclature to expressly recite specific enantiomers of a new chemical entity.
The Patent At Issue
The patent as issue was Sunovion’s (a U.S. subsidiary of Sumitomo Dainippon) U.S. Patent 5,532,372, which is listed in the Orange Book for Latuda®. The claims are generally directed to specific imide compounds and their acid addition salts. Claim 14, the claim at issue for infringement, recites an imide compound of the formula:
Lurasidone, the (–)-enantiomer of the above imide compound, is the active ingredient in Latuda®.
Example 1-(a) of the specification illustrates the above imide compound as Compound No. 101. Examples 1(b) and 1(c) detail the process for obtaining the (+)-enantiomer (Compound No. 102) and (–)-enantiomer (Compound No. 103), respectively, in the tartrate salt form. Example 1(d) produces the hydrochloride salt form of (+)-enantiomer (Compound No. 104), and Example 1(e) produces the hydrochloride salt form of the (–)-enantiomer (Compound No. 105), from Compound Nos. 102 and 103, respectively. Compound No. 105 is lurasidone.
The District Court Proceedings
According to the Federal Circuit decision, the district court’s claim construction analysis centered on “what combination of enantiomers claim 14 encompassed.”
Appellants sought to limit claim 14 to “a racemic mixture of two enantiomers of which the structural formula is representative,” relying on the structure’s similarities to Compound No. 101 (which Appellants alleged to be a racemic mixture), representations of racemic mixtures in organic chemistry textbooks, and the patent’s prosecution history. The district court rejected that construction, finding that resemblance to Compound No. 101 did not justify importing a “racemic” limitation from the specification into the claim. Instead, the court adopted Sunovion’s proposed construction, whereby claim 14 encompassed any enantiomer or mixture thereof, i.e., “lurasidone, lurasidone’s enantiomer, as well as mixtures of these enantiomers.”
The Federal Circuit Decision
The Federal Circuit opinion was authored by Judge Stoll, and joined by Judges Moore and Mayer.
The Federal Circuit started its analysis with the plain language of the claims:
Both parties agree that the structure shown in the claim is the (–)-enantiomer; moreover, Appellants do not dispute that a person of ordinary skill looking at claim 14’s structure in a vacuum would understand it to be one way of depicting the (–)-enantiomer. Of equal importance is the lack of anything in the claim language limiting its scope to a “racemate” or “racemic mixture.”
Then, the Federal Circuit looked to the specification:
Instead of suggesting that the (–)-enantiomer should be excluded, the specification describes it as a preferred embodiment. Although its structure is not shown, Example 1(e) details the steps for obtaining Compound No. 105, the (–)-enantiomer, from Compound No. 101 and even provides data on Compound No. 105’s physical properties.
The Federal Circuit concluded,“[T]he intrinsic record supports including the (–)-enantiomer…within claim 14’s scope.”
In support of its analysis, the Federal Circuit cited the precedential decision in Pfizer, Inc. v. Ranbaxy Laboratories Ltd., 457 F.3d 1284, 1288–89 (Fed. Cir. 2006), where the it had rejected Ranbaxy’s arguments to limit a claim depicting a specific three-dimensional orientation to a racemic mixture, and instead construed it to cover the R- and S-trans enantiomers as well as any mixtures of the two, but not the cis isomers which were specifically disclaimed in the specification.
With regard to Appellants’ arguments based on Compound No. 101, the Federal Circuit explained:
In our view, the specification is inconclusive regarding whether Compound No. 101 is a racemic mixture. …. Even if Compound No. 101 is a racemic mixture, the specification neither defines claim 14’s structure as Compound No. 101 nor disclaims scope in a way that confines claim 14 to a racemic mixture.
The Federal Circuit also dismissed Appellants’ extrinsic evidence from textbooks and expert testimony as being “less significant than the intrinsic record in determining ‘the legally operative meaning of claim language.’” The Federal Circuit noted that “while Appellants’ expert contends that it is conventional in the art to use a single enantiomer as shorthand for a racemic mixture, he does not state that a person of ordinary skill would always understand the depiction of single enantiomer to exclude the very enantiomer depicted.” Thus, the Federal Circuit concluded:
The district court did not err in construing claim 14 to cover the (–)-enantiomer. Determining whether claim 14 covers additional scope is unnecessary to the disposition of this appeal.
What’s in a name?
The Federal Circuit summarized the case as follows:
The district court construed the claim to cover the two three-dimensional orientations in isolation—both the one shown in the claim and its mirror image—as well as mixtures of the two in any ratio. The parties then stipulated to infringement and the entry of an injunction. We agree that, at a minimum, the claim encompasses the specific
orientation depicted. Because this orientation is the active pharmaceutical ingredient in each party’s commercial product, we need not determine what else falls within the claim’s ambit to resolve the present dispute.
Even with this positive outcome for the patent owner, this case highlights that while presenting chemical structures with three-dimensional notations can be helpful, it also can be useful to use nomenclature–labels and/or descriptive text–to describe specific enantiomers. This case demonstrates that graphical representations of stereochemistry may be open to interpretation, and suggests that using words or labels to identify stereochemical configurations (R, S, d, l, (-), (+) etc.) may help avoid doubt as to claim scope.