Eisai Inc v. Crystal Pharmaceutical Suzhou Co Ltd

1. Case Identification

• Case #: PGR2021-00047
• Patent #: 10,759,779
• Filed: February 3, 2021
• Petitioner(s): Eisai Inc.
• Patent Owner(s): Crystal Pharmaceutical (Suzhou) Co., Ltd.
• Challenged Claims: 1-4, 7-8

2. Patent Overview

• Title: Crystalline Form of (1R,2S)-2-{[(2,4-Dimethylpyrimidin-5-yl)oxy]methyl}-2-(3-fluorophenyl)-N-(5-fluoropyridin-2-yl)cyclopropanecarboxamide
• Brief Description: The ’779 patent discloses and claims a specific crystalline form of the compound lemborexant, designated "crystalline form CS2." The claims define this polymorph by its characteristic peaks in an X-ray powder diffraction (XRPD) pattern. Lemborexant is an orexin receptor antagonist used for the treatment of insomnia.

3. Grounds for Unpatentability

Ground 1: Inherent Anticipation of Claims 1-4 under 35 U.S.C. §102

• Prior Art Relied Upon: Eisai (Patent 9,416,109).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner argued that the procedures for synthesizing lemborexant disclosed in Example G of the ’109 patent inherently and inevitably produce the claimed crystalline form CS2. The ’109 patent describes two detailed methods for preparing lemborexant: a "first procedure" and an "alternate procedure." Petitioner contended that the final purification step in both procedures—dissolving lemborexant in ethyl acetate and precipitating it with the anti-solvent n-heptane—is a crystallization process that necessarily results in the specific polymorph claimed in the ’779 patent. To support this, Petitioner submitted declarations and experimental evidence from its experts, who replicated both procedures from the ’109 patent. The resulting material was analyzed via XRPD, and the data allegedly demonstrated a direct match with the characteristic peaks of the claimed crystalline form CS2. Petitioner also presented evidence from its own internal manufacturing records, showing that batches of lemborexant produced as early as 2010 using procedures consistent with the ’109 patent also resulted in the claimed crystalline form CS2.

Ground 2: Obviousness of Claims 7 and 8 under 35 U.S.C. §103

• Prior Art Relied Upon: Eisai (’109 patent) in view of Eisai (International Publication No. WO 2016/063995, the “’995 publication”).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner asserted that the ’109 patent teaches efficient and cost-effective methods for preparing crystalline lemborexant, which inherently results in the form CS2 claimed in the ’779 patent. The ’995 publication, which published before the ’779 patent’s priority date, discloses using lemborexant to treat insomnia. Specifically, it teaches formulating a "therapeutically effective amount" of lemborexant with pharmaceutically acceptable carriers into oral dosage forms (e.g., tablets) and provides positive clinical study results demonstrating its efficacy. Claim 7 recites a pharmaceutical composition comprising a therapeutically effective amount of crystalline form CS2, and Claim 8 recites a method of treating insomnia by administering it. Petitioner argued these claims are obvious by combining the teachings of the two references.
  • Motivation to Combine: A person of ordinary skill in the art (POSA), seeking to develop a drug for insomnia, would have been motivated to use the efficient synthesis method for the active pharmaceutical ingredient (crystalline lemborexant) from the ’109 patent and formulate it as taught by the ’995 publication for its demonstrated therapeutic use.
  • Expectation of Success: The favorable clinical trial data disclosed in the ’995 publication would have provided a POSA with a strong and reasonable expectation that a pharmaceutical composition containing lemborexant made via the ’109 patent's methods would be successful in treating insomnia.

Ground 3: Obviousness of Claims 1-4 under 35 U.S.C. §103

• Prior Art Relied Upon: Eisai (’109 patent).
• Core Argument for this Ground:
  • Prior Art Mapping: As an alternative to its anticipation argument, Petitioner argued that claims 1-4 are obvious over the ’109 patent alone. A disclosure that anticipates also renders a claim obvious. Petitioner asserted that even if the Patent Owner were to identify minor, unstated process details to argue against inherent anticipation, it would have been obvious for a POSA to practice the detailed, step-by-step procedures described in Example G of the ’109 patent to prepare lemborexant.
  • Motivation to Combine (Rationale): The motivation was simply to prepare the known and useful compound, lemborexant, using the precise and enabling methods disclosed in the prior art for its synthesis.
  • Expectation of Success: Given the detailed and routine nature of the chemical synthesis and purification techniques described in Example G of the ’109 patent, a POSA would have had a high expectation of successfully preparing lemborexant by following the disclosed procedures. The natural and obvious result of this successful preparation is the claimed crystalline form CS2.

4. Arguments Regarding Discretionary Denial

• Petitioner argued that the Board should not exercise its discretion to deny institution under 35 U.S.C. §325(d). The petition asserted that the core arguments and evidence were never substantively considered by the USPTO. Specifically, the Examiner was only presented with the number of the Chinese counterpart to the ’109 patent as part of an Information Disclosure Statement (IDS) and made a generalized statement of allowance without any substantive analysis of its teachings. Furthermore, Petitioner’s inherent anticipation argument and the crucial supporting experimental evidence (XRPD data) demonstrating the inevitable result of the ’109 patent's procedures were entirely new and not before the Examiner during the expedited prosecution.

5. Relief Requested

• Petitioner requests institution of post-grant review and cancellation of claims 1-4, 7, and 8 of the ’779 patent as unpatentable.