Overview
On June 23, in Enanta Pharmaceuticals, Inc. v. Pfizer Inc., the Federal Circuit affirmed summary judgment ruling that all claims of Enanta’s U.S. Patent No. 11,358,953 (’953 patent) were invalid as anticipated. The Federal Cricut held that Enanta’s ’953 patent was not entitled to the priority date of its earlier-filed provisional application because the provisional application lacked adequate written description support for the claimed subject matter.
Background
The case involved Enanta’s ’953 patent, directed to antiviral compounds and methods for inhibiting coronavirus replication. The patent issued from a non-provisional application filed on November 9, 2021, and claimed priority from U.S. Provisional Patent Application 63/054,048 (’048 provisional) filed on July 20, 2020. A critical difference between the two disclosures was the definitions for the terms “substituted” and the chemical groups that qualify as “substituents.” Specifically, the ’048 provisional described a range of carbon atoms as C2–C12, whereas the ’953 patent expanded the range to C1–C12. Meanwhile, on April 6, 2021, Pfizer publicly disclosed nirmatrelvir, a compound falling within the broader C1–C12 range and later used in Paxlovid®.
The Priority Dispute
On July 9, 2021, Enanta contended that it realized the ’048 provisional contained a typographical error and should have read “C1” and not “C2” all along. Enanta sued Pfizer alleging Paxlovid® infringed the claims of the ’953 patent. The district court granted Pfizer’s motion for summary judgement that asserted the claims of the ’953 patent were invalid because they were not supported by the ‘048 provisional’s disclosure. Enanta appealed.
Federal Circuit Analysis
Here, the Federal Circuit focused on whether the ’048 provisional application satisfied the written description requirement of 35 U.S.C. § 112 to entitle the asserted claims to its priority date. The Federal Circuit rejected Enanta’s argument that the discrepancy was an obvious typographical error, emphasizing that the ’048 provisional specification did not specifically disclose the claimed C1-C12 substituent and referred only to C2–C12. Expert testimony suggesting a broader interpretation or identifying inconsistencies elsewhere in the document was unpersuasive because entitlement to priority depends on what was actually disclosed. The court concluded that a disclosure of one chemical compound is not necessarily a disclosure of a different compound, and Enanta did not invent what was not disclosed. Accordingly, the patent was not entitled to the earlier priority date, and Pfizer’s intervening disclosure anticipated the claims.
Key Takeaways
This case reinforces several key principles: (1) priority requires strict written description support for the claimed subject matter; (2) courts are reluctant to treat discrepancies as correctable errors unless they are indisputably obvious; (3) even small numerical changes in chemical ranges can materially alter claim scope; and (4) intervening public disclosures can invalidate patents when priority claims fail. For patent practitioners and owners, this case highlights the importance of careful drafting, consistency across applications, and early identification and correction of errors.
For more information on this topic, please contact Fitch Even associate Lindsay Boehme, author of this alert.
Fitch Even IP Alert®
Lindsay Boehme, Ph.D.
Lindsay Boehme, Ph.D., is a skilled Technical Writer with expertise in patent application preparation and prosecution across a range of scientific and engineering disciplines. Her work draws on more than a decade of experience in chemical engineering, materials science, and electrochemical technology development.