Enanta Pharmaceuticals, Inc.

Federal Circuit Rules Typographical Error in Provisional Application Spoils Priority Date, Invalidating Enanta Patent Against Pfizer's Paxlovid

- The Federal Circuit affirmed that Enanta's US11358953 patent is not entitled to its July 2020 provisional priority date due to inadequate written description support. - The provisional application disclosed a substituent as —NHC(O)—C2–C12-alkyl, while the issued patent claimed —NHC(O)—C1–C12-alkyl, adding the one-carbon species matching nirmatrelvir. - Because the C1 group was never disclosed in the provisional filing, Pfizer's April 2021 public disclosure of nirmatrelvir constituted intervening prior art that anticipated the claims. - The court rejected Enanta's argument that "C2" was an obvious typographical error, holding that C2 does not provide written description support for C1.