Anticipation of Salt Selection Patents After Mylan Pharms. Inc. v. Merck Sharp & Dohme Corp.

Mylan Pharms. Inc. v. Merck Sharp & Dohme Corp., 2022 WL 4541687 (Fed. Cir. Sept. 29, 2022)

Are species claims important to your business and has the genus encompassing your species been disclosed? Are you considering invalidating a species claim based on a prior disclosure of that species in a relatively broad genus? If you answered yes to either question, this Federal Circuit decision will have an impact on you.

It is black letter law that a prior art disclosure of a chemical species anticipates a chemical genus encompassing that species. However, the opposite is not necessarily true. For the purpose of anticipation, a genus will be found to anticipate, i.e. disclose each species of that genus, only if a person of ordinary skill can “at once envisage each member of this limited class.” In re Petering, 301 F.2d 681 (C.C.P.A. 1962).

Recently, the Court in Mylan v. Merck addressed the boundaries of “limited” in the context of the Petering holding. The Court found that a 1:1 stoichiometric salt form of a prior art compound, sitagliptin DHP salt, described within a genus of 957 potential salt forms was not anticipated. Various articles describing this Decision have focused on the “limited” term, but perhaps there is more here than meets the eye.

In an attempt to market a generic version of JANUVIA®, a drug product used to treat non-insulin-dependent (i.e., Type 2) diabetes which generates multiple billions in sales, Mylan petitioned for inter partes review (IPR) of Claim 1 of Merck’s U.S. Patent 7,326,708 (the “’708 patent”), which recites:

1. A dihydrogenphosphate salt of a 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 Formula I:

or a hydrate thereof.

In the IPR Petition, and at the Federal Circuit, Mylan argued that a 1:1 sitagliptin DHP salt, a species of Claim 1, was anticipated or rendered obvious based on an earlier genus disclosure. That earlier disclosure included a list of 33 compounds, one of which was sitagliptin. That disclosure also recited eight “preferred salts,” one of which was a phosphate salt, the salt used in 1:1 sitagliptin DHP. This list of compounds and salts results in 264 different chemical compounds, which when taken in combination with the varying stoichiometric ratios of sitagliptin to phosphate, results in a disclosed genus of 957 different salts. Claim 1 of the patent-at-issue is one of those 957 possible salt compounds.

Merck argued that the genus disclosure of 957 salt compounds did not make it possible for one of ordinary skill to be able to “at once envisage each member” (emphasis added) of that genus. The Court noted that Mylan unsuccessfully attempted to focus “on whether skilled artisans could have envisaged 1:1 sitagliptin DHP among the members of the class instead of envisaging each member of the disclosed class.” (emphasis added). And that one of ordinary skill was not able to envisage each of the 957 possible salt compounds, some of which the Court notes may not even be possible to make under experimental conditions. Notably, the Court relied on Mylan’s own expert admission that salt formation based on the disclosed genus is “an unpredictable art” that requires a “trial-and-error process.” Due to the inability to form some of the possible species, and due to the unpredictability of performing a trial-and-error discovery process, those of skill in the art would not be able to imagine “each member” of that disclosed genus.

Mylan’s argument that a skilled artisan could imagine the one specific salt at issue was rejected. It appears that to succeed, Mylan would have had to show that a prior genus disclosing one species and multiple possible salt forms would have led one of ordinary skill in the art to envision all the individual salt forms. So, Mylan would have had to establish that, not only is the number of species in the genus “limited”, but also that a skilled artisan could envision “each member” of that genus.


If you own an issued patent directed to a chemical species, it would be prudent to review prior genus disclosures (especially from the same Applicant and same Inventors) to ensure that (1) earlier genus disclosures do not establish a roadmap to “each member” of a predictably formed, small number of easily created species; and (2) earlier genus disclosures are sufficiently broad such that there is no “limited” class of species disclosed by the genus.

If you are challenging the validity of a patent based for anticipation by a prior art, disclosed genus, be prepared to show (1) that the disclosed genus has a limited number of species, and (2) that one of ordinary skill would have an easy, straight forward task to envision and create all species members experimentally.

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