Federal Circuit Develops The 'At Once Envisage' Standard Of Anticipation And Affirms The Importance Of Specialized Considerations In The Chemical Arts

• Published date: 14 November 2022
• Subject Matter: Intellectual Property, Patent
• Law Firm: BakerHostetler
• Author: Michael Schwartz Ph.D.

Anticipation of a claim generally requires that a single prior art reference explicitly discloses each and every claim element.¹ However, absent an express teaching in the prior art, a claim may also be anticipated if it is directed to a member of a limited class that a person of ordinary skill in the art would "at once envisage" from the teachings of the reference.² The U.S. Court of Appeals for the Federal Circuit recently provided more guidance on the bounds of its "at once envisage" standard in affirming a notable Patent Trial and Appeal Board (PTAB) decision.

In Mylan Pharms. Inc. v. Merck Sharp & Dohme Corp.,³ Mylan appealed a PTAB decision finding the claims of Merck's U.S. Patent No. 7,326,708 ('708 patent) novel over a single prior art reference. The claims at issue relate to a 1:1 sitagliptin dihydrogenphosphate (DHP) salt.⁴ Claim 1 of the '708 patent is directed to:

A dihydrogenphosphate salt of 4-oxo-4-[3-(trifluoromethyl)-5,6-dihydro[1,2,4]triazolo[4,3-a]pyrazin-7(8H)-yl]-1-(2,4,5-trifluorophenyl)butan-2-amine of structural formula I:

or a hydrate thereof.

During the inter partes review, Mylan argued that one of Merck's prior art publications⁵ - describing (R)-sitagliptin hydrochloride among 33 other exemplified compounds - anticipated the 1:1 sitagliptin DHP salt because the reference provides two closed lists containing both 33 compounds and eight preferred acids for forming the salts. Mylan asserted the prior art's disclosure "collapse to form a single comprehensive list of all the compounds and salts."⁶ However, relying on the testimony of Merck's expert, the PTAB disagreed, finding that Mylan's position did not account for the numerous potential stoichiometric ratios of the salts, which could result in approximately 957 salts.⁷ The PTAB also found that Mylan's position was undermined by its own experts, who did not "at once envisage" each member of sitagliptin phosphate salts and whose testimony contradicted the evidence which "undeniably shows that non-1:1 sitagliptin phosphate salts do exist."⁸ As a result, the PTAB found that the claims directed to sitagliptin DHP were not anticipated due to both a lack of express disclosure and the inability of a person of skill in the art to envisage all the possible salts that could be generated from the prior art's disclosure.

On appeal, the Court stated that in the context of anticipation where a skilled artisan may "at once envisage each member of [a] limited class" that "[t]he key term here is...