"[T]he same claim term can have different constructions depending upon the context of how the term is used within the claims and specification."

On May 20, 2013, in Aventis Pharms., Inc. v. Amino Chems. Ltd., the U.S. Court of Appeals for the Federal Circuit (Newman, Bryson, Reyna*) reversed and remanded the district court's judgment that Amino, Dipharma, Mylan and Teva did not infringe U.S. Patent No. 5,750,703, which related to various piperidine derivatives commonly used as active ingredients in antihistamines. The Federal Circuit stated:

"It is a bedrock principle of patent law that the claims of a patent define the invention to which the patentee is entitled the right to exclude." There is a heavy presumption that claim terms are to be given their ordinary and customary meaning. Courts are required therefore to "look to the words of the claims themselves . . . to define the scope of the patented invention." Claims, however, must be construed in light of the appropriate context in which the claim term is used. The written description and other parts of the specification, for example, may shed contextual light on the plain and ordinary meaning; however, they cannot be used to narrow a claim term to deviate from the plain and ordinary meaning unless the inventor acted as his own lexicographer or intentionally disclaimed or disavowed claim scope. The prosecution history too, as part of the intrinsic record, has an important role in claim construction by supplying context to the claim language. While the prosecution history "lacks the clarity of the specification and thus is less useful for claim construction purposes", it still provides evidence of how the inventor intended the term to be construed.

Claims 1, 6, and 7 of the '703 patent explicitly include the term "substantially pure regioisomer." The district court construed this language to require "at least 98% purity with respect to all impurities." This construction, however, conflates the purity required for the piperidine end product with that of the CPK [(cyclopropylketone)] intermediate. We agree with both parties that the claims themselves are insufficient to define the term "substantially pure." Therefore, we must turn to other sources of intrinsic evidence to determine "what the inventors actually invented and intended to envelop with the claim." The specification provides the "best source" for construing a claim term and determining the inventor's intent regarding use. In this case, the specification does not provide an explicit definition of the term "substantially pure" or "substantially pure regioisomer." The district court determined that because the term "substantially pure" is used indiscriminately with regards to the CPK intermediate and the piperidine derivative end product throughout the specification, "substantially pure" should have only one construction throughout the patent. The "one construction throughout the patent" rule adopted by the district court is incorrect. [T]he same claim term can have different constructions depending upon the context of how the term is used within the claims and specification. While "substantially pure" refers to both the CPK intermediate and the piperidine derivative end product in the specification, the term "substantially pure" is used only in reference to the CPK intermediate in relevant claims 1, 6, and 7. And unlike other patents in the family, there is no explicit "substantially pure" limitation placed on the piperidine derivative end product in the relevant claims of the '703 patent. The lack of any "substantially pure" limitation on the piperidine derivative end products in claims 1, 6, and 7 obviates any explicit requirement to apply a construction of "substantially pure" that is consistent for both the CPK intermediate and the piperidine derivative end product. Further, a person of ordinary skill in the art would recognize that an intermediate of the claimed chemical reaction would not be required to have the same purity as the end product. . . . Interpreting this specification in light of the knowledge of a person of ordinary skill in the art, we hold that a proper construction requires different interpretations of "substantially pure" when applied to the CPK intermediate and piperidine derivative end product.

The "one-size-fits-all" construction adopted by the district court incorrectly construes "substantially pure" separate from the very next word -- "regioisomer." The district court's artificial truncation of the claim term for the expediency of a single interpretation across different contexts was error. [The] uniform use of "substantially pure regioisomer," taken as a whole, exposes the error of the district court: by decoupling the modifier "substantially pure" from "regioisomer" for purposes of claim construction, the district court imposed a single interpretation even though that context requires separate definitions of "substantially pure" when applied to the CPK intermediate as opposed to the piperidine derivative end product. We thus conclude that the district court erred in requiring that "substantially pure" have the same interpretation when applied to the CPK intermediate and the piperidine derivative end product.

The presumption is that claim terms should be given their "ordinary and customary meaning," and not a restrictive construction unless there is clear evidence to support it in the intrinsic evidence, or a broader meaning is specifically disclaimed during prosecution. . . . We hold that the modifier "substantially pure," when construed in light of a person of ordinary skill in the art and in view of the claimed improvements over the prior art, only applies regioisomeric impurities, not all impurities.

With no explicit construction of the term "substantially pure" in the claims, specification, or prosecution history, we apply the "ordinary and customary" definition to the claim term. In other contexts, this court has interpreted "substantially" as a non-specific term of approximation that avoids a numerical boundary. . . . "Largely but not wholly" is consistent with a flexible approach to regioisomeric purity for an intermediate, is faithful to the specification's silence regarding numerical precision and, most importantly, is not arbitrarily tied to the FDA standard for pharmaceutical-grade end products. No one ingests the intermediate compound, so there is no reason to impose end-product purity on it. Therefore, we adopt the Appellants' proposed construction of "substantially pure regioisomer of the following formula" as used in the '703 patent and construe the term to mean "largely but not wholly the para regioisomer of the intermediate of the structure shown, as compared to the meta isomer." Because the district court erred in construing "substantially pure" as used in the '703 patent, we reverse and remand.