In Enanta Pharmaceuticals, Inc. v. Pfizer, Inc., [2025-1427] (June 23, 2026), the Federal Circuit affirmed that all claims of Enanta’s U.S. Patent No. 11,358,953 were invalid as anticipated.
The ‘953 patent claimed priority to a prior provisional patent application that disclosed NHC(O)-C2-C12-alkyl while the ‘953 patent claimed NHC(O)-C1-C12-alkyl. Enanta conteded that it discovered the typographical error in July 9, and filed the application for the ‘953 patent on July 19. The problem was that on April 6 Pfizer made a public disclosure of NHC(O)-C1-alkyl.
The Federal Circuit characterized the issue as “whether ‘2’ provides adequate written description support for ‘1’.” The Federal Circuit said that this was not a case of the correction of an obvious error, noting that the change from C2 to C1 had not been showed here to be a correction of an obvious error, and that the correction was certainly subject to reasonable debate.
The Federal Circuit concluded that the ‘048 provisional does not convey to a skilled artisan that the inventors possessed the NHC(O)-C1-alkyl at the time of filing of the provisional application. The Court observed that “C2 is simply different from C1.” The entitlement to a filing date extends only to that which is disclosed. The Federal Circuit found no genuine issue of material fact, and affirmed summary judgment in favor of Pfizer.