By Kevin E. Noonan –

Measurement of the hydrogen ion concentration in an aqueous solution is represented (on a logarithmic scale) as the pH, wherein water under ambient conditions (a temperature of 25°C) has a neutral pH of 7 and the solution becomes more acidic as the pH value trends towards 1 and more basic as it trends towards 14.  Characterizing such solutions as elements of patent claims has a long judicial history (being critical in the seminal case on the doctrine of equivalents, Warner-Jenkinson Co., Inc. v. Hilton David Chemical Co.) and the property was recently the basis of the Federal Circuit’s decision in Biofer S.P.A. v. Vifor (International) AG (non-precedential).

The case arose in patent infringement litigation wherein Biofer filed suit asserting U.S. Patent No. 8,759,320, directed to trivalent iron complexes with various forms of sugars (specifically dextrins and dextrans).  Claim 1 was set forth in the opinion as being representative:

1.  A process for the preparation of an activated sugar comprising the step of reacting a sugar having an aldehyde end group with bromine in a solution at a pH between 7.0 and 9.0 with the specific oxidation of the end aldehyde, wherein

i) said sugar is selected from the group consisting of dextrins and dextrans and wherein

ii) said bromine is produced in situ through the addition of a hypochlorite and an alkaline or earth alkaline metal bromide to said solution, said hypochlorite being added in stoichiometric quantities with respect to the aldehyde end groups, wherein said hypochlorite is added instant by instant, such that  an excess of hypochlorite in solution is never present.

The invention provided an improvement on prior art processes for producing complexes for treating iron deficiencies that accommodate required “fundamental characteristics, such as physical and chemical stability, low toxicity, and good bioavailability” necessary for therapeutic use.  Of the four synthetic steps required in the process, the claims (and appeal) were directed to activating the sugar for producing an iron complex.  This activation step was illustrated in the diagram:

which was accomplished by performing the claimed oxidation reaction with bromine in solution.  The opinion also explains that specific aldehyde moieties in dextrins and dextrans are advantageous (i.e., at the ends of the sugar polymer) because permitting the reaction to proceed elsewhere in the sugar molecule was associated with undesirable instabilities.  In practice, correct oxidation required a solution pH “in the range between 5.0 and 12.0, preferably, between 7.0 and 9.0.”

The District Court construed the pH limitation and practice of the synthetic methods falling within the scope of claim 1 to mean that the pH range of 7.0 to 9.0 must be maintained throughout the process, based on the intrinsic evidence and in particular the disclosure in the specification (see below).  Because discovery revealed that Vifor’s process only maintained a pH within the construed range “approximately 90% of the time,” Biofer stipulated that the accused process did not infringe (while informing the District Court of its intention to appeal).

In that appeal the Federal Circuit affirmed, in an opinion by Judge Reyna joined by Judges Linn and Dyk.  Beginning with the claim language, the opinion asserts that the plain meaning of the phrase “at a pH between 7.0 and 9.0” modifies “the step of reacting a sugar” and that this “step” refers to “the entire oxidation step” of the disclosed synthetic process.  The disclosure of the specification is consistent with this interpretation, in the panel’s view, wherein it recited that “to avoid undesirable depolymerization, ‘it is important to maintain the reaction pH in the range between 5.0 and 12.0, preferably, between 7.0 and 9.0′” (albeit this phrase could just as easily be reasonably construed to mean that the reaction be maintained in the range of pH 5.0 to 12.0).  Elsewhere in the specification, however, the “maintain” limitation is restricted to a pH range of 7.0 to 9.0, supporting the District Court’s construction, further supported by the three examples expressly directed to performance of the oxidation step being achieved between pH 7.0 and 9.0.  The Federal Circuit relied upon GPNE Corp. v. Apple Inc., 830 F.3d 1365, 1370 (Fed. Cir. 2016) (quoting VirnetX, Inc. v. Cisco Sys., Inc., 767 F.3d 1308, 1318 (Fed. Cir. 2014)), for the principle that when a patent “‘repeatedly and consistently’ characterizes a claim term in a particular way” that is the proper way the term should be construed.  Finally, the prosecution history was consistent with this conclusion, wherein Biofer had submitted an expert declaration attesting that performing the oxidation reaction between pH 7.8 and 8.2 was “highly selective without increasing depolymerization,” while performing the reaction between 9.8 and 10.2 “led to a depolymerizing attack on the sugar.”

Biofer argued that the District Court’s construction improperly relied upon a preferred embodiment (pH 7.0 to 9.0) instead of construing the pH range throughout it entire scope (pH 5.0 to 12.0).  The panel acknowledged the broader pH range, but the claim having only recited the narrower pH 7.0 to 9.0 range was dispositive for the Court.  Further (oral) argument that the process could be construed to permit the pH to encounter “brief excursions” outside the narrower range but within the broader range was precluded by Biofer’s failure to raise this argument below according to the opinion, citing Conoco, Inc. v. Energy & Env’t Int’l, L.C., 460 F.3d 1349, 1358–59 (Fed. Cir. 2006) (it not helping Biofer’s argument that it had raised what appeared to the panel to be an opposite argument before the District Court).

Biofer S.P.A. v. Vifor (International) AG (Fed Cir. 2026)
Nonprecedential disposition
Panel: Circuit Judges Dyk, Linn, and Reyna
Opinion by Circuit Judge Reyna