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ARTICLE · 16 JULY 2026

Federal Circuit: Provisional Application Must Support Later Claims

Lerner David Littenberg Krumholz & Mentlik, LLP
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The Federal Circuit addressed whether a patent claiming priority to a provisional application can maintain that earlier filing date when the provisional disclosed a C2-C12 alkyl substituent but the issued patent broadened the claim to C1-C12 alkyl. This case examines the written description requirement and its impact on priority dates in pharmaceutical patent disputes, particularly where an intervening public disclosure by a competitor falls between the two filing dates.

United StatesIntellectual Property
Hayley Yang
Hayley Yang
Nicholas Bougher
Nicholas Bougher
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In Enanta Pharmaceuticals, Inc. v. Pfizer Inc., No. 2025-1427 (Fed. Cir. June 23, 2026), the Federal Circuit affirmed that a patent is not entitled to its provisional application’s priority date where the provisional application fails to provide adequate written description support for what is claimed in the patent.

Enanta accused Pfizer’s Paxlovid® of infringing U.S. Patent No. 11,358,953, which is directed to compounds and methods for inhibiting coronavirus replication. The ’953 patent issued from a non-provisional application filed on November 9, 2021 and claimed priority to a provisional application filed on July 20, 2020. The provisional application disclosed a substituent as —NHC(O)—C2–C12-alkyl, but the non-provisional recited —NHC(O)—C1–C12-alkyl. Between the two filings, Pfizer publicly disclosed nirmatrelvir, the active ingredient in Paxlovid®, which bears a C1-alkyl group.

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