Did I Write That? Enanta and the Written Description Requirement
The recent decision by the U.S. Court of Appeals for the Federal Circuit in Enanta Pharmaceuticals, Inc. v. Pfizer Inc.,[1] demonstrates the importance of fully complying with the written description requirement[2] for patent applications and correctly capturing each aspect of an invention in an initial disclosure. A patent application lacking critical details of an invention may suffer a variety of consequences including loss of priority date and, consequently, invalidation of the granted patent in litigation.
In Enanta, the Federal Circuit affirmed a district court judgment invalidating Enanta’s patent claims to a group of coronavirus protease inhibitor compounds containing an —NHC(O)—C1-C12-alkyl group, i.e., a group containing from 1 to 12 carbon atoms. In July 2020, Enanta filed a provisional application which described compounds containing C2-C12 (i.e., not C1-C12) alkyl groups. Subsequently, in July 2021, they filed a non-provisional utility application that claimed the priority benefit of the filing date of the earlier-filed provisional application. The non-provisional utility application extended the claimed compound to include C1-C12 alkyl groups. After multiple continuations, Enanta’s patent claiming C1-C12 alkyl groups (i.e., not C2-C12 as disclosed in the provisional application) was granted.
However, in April 2021, between the filing dates of the provisional and non-provisional utility applications, Pfizer disclosed the drug nirmatrelvir, which includes a one-carbon (i.e., C1) alkyl group.
Enanta sued Pfizer in June 2022 for infringement of its patent based on Pfizer’s drug nirmatrelvir. Pfizer asserted in defense that Enanta’s patent was invalid for anticipation because the “new” subject matter disclosed and claimed in the non-provisional application – that is, the compound with a C1 alkyl group -- was not entitled to the priority benefit of the provisional application’s filing date, because the provisional application only disclosed compounds having C2-C12 alkyl groups. Although Enanta alleged that the disclosure of C2-C12 in the provisional application was a typographical error that was subsequently corrected in the non-provisional utility application, the trial court agreed with Pfizer that the disclosure of “C2-C12” was not an obvious, and correctable, error and that the change of “C2” to “C1” would broaden the scope of the provisional application’s disclosure. Enanta’s patent claims were, therefore, not entitled to the claimed priority date and Pfizer’s intervening disclosure of the drug nirmatrelvir anticipated the patent claims in suit, rendering them invalid.
On appeal, the Federal Circuit affirmed the district court, further commenting on the requirements for written description in patent applications. The court noted that C2 is, in fact, different from C1 and that the disclosure of C2 did not meet the Section 112 written disclosure requirement of conveying to one skilled in the art that the inventors had possession of the C1 variant at the time of filing the provisional application. Furthermore, the Federal Circuit observed that the provisional application was “highly detailed, providing dozens of specific chemical moieties presumably described with great care” (emphasis added) and offered no indications that a skilled artisan would readily recognize “C2” as being a typographical error of “C1”. Analogizing, the court offered the example that the two-carbon alcohol, ethanol, is regularly consumed by people while the one-carbon alcohol, methanol, is highly toxic to humans. This example illustrates why a difference of one consecutive number – 1 instead of 2 – could not be considered sufficiently similar that the disclosure of “C2” supports the implicit disclosure of “C1.”
Enanta serves as a reminder to practitioners and inventors that it is critical to ensure that the original, first filing of a patent application – even as a provisional application – contains a clear and complete and accurate description of the full scope of the invention for which protection is desired. While it is possible in very narrow circumstances to correct errors in filed provisional and non-provisional applications, the frequency of such circumstances is exceptionally low. Moreover, the error being corrected must be of such a nature that one skilled in the art would consider the correction to be “obvious” and “not subject to reasonable debate.” It is especially important when including ranges for features and properties that the values encompassed by the ranges be reviewed to ensure that the ranges encompass at least the invention itself, but also conceivable variants of the invention prior to filing an application. Failure to include a description of the full scope of the invention, as well as any possible variants, for which future protection may be sought, may result in the loss of patent rights, as happened to Enanta in this case.
