October 17, 2022by Jacob Doughty

Mylan Pharm. v. Merck Sharp & Dohme Corp., No. 2021-2121 (Fed. Cir. Sep. 29, 2022), is a recent decision of the Federal Circuit considering, inter alia, whether a prior art disclosure of a genus of salts was sufficient to anticipate or render obvious a single salt species.

In an Inter Partes Review proceeding before the PTAB, Mylan asserted that claims of a Merck patent were anticipated by or obvious over a prior Merck patent publication, Edmondson. The PTAB concluded that Mylan failed to prove unpatentability, and Mylan appealed. The claims of the Merck patent at issue were directed to sitagliptin dihydrogenphosphate (DHP). Exemplary claims include claims 1, 2, and 4:

1. A dihydrogenphosphate salt of a 4-oxo-4-[3-(trifluoromethyl)-5,6-dihydro [1,2,4]tria-zolo[4,3-a]pyrazin-7(8H)-yl]-1-(2,4,5-tri-fluorophenyl)butan-2-amine… or a hydrate thereof.

2. The salt of claim 1 of structural formula II having the (R)-configuration at the chiral center marked with an *


4. The salt of claim 2 characterized in being a crystalline monohydrate.

Edmondson disclosed sitagliptin in a list of 33 compounds. Edmondson further disclosed acids forming pharmaceutically acceptable salts including phosphoric acid in a list of eight preferred acids. Mylan argued that this was sufficient to anticipate claim 1, relying on the reasoning of In re Petering, 301 F.2d 676, 681 (C.C.P.A. 1962) (prior art may be deemed to disclose each member of prior art genus when skilled artisan can “at once envisage each member of this limited class”).

Merck countered that the combined list of 33 compounds and eight preferred salts, taking into account various stoichiometric possibilities, encompassed  957 salts, which was not sufficient for a skilled artisan to “at once envisage” the salt of claim 1.

The Federal Circuit agreed with Merck that Edmondson did not “expressly disclose a 1:1 sitagliptin DHP salt.” The Federal Circuit credited expert testimony (including testimony of Mylan’s own expert) that Edmondson did not direct a skilled artisan to sitagliptin among the list of 33 compounds and did not single out phosphoric acid or any phosphate salt among the enumerated salts. The Federal Circuit noted particularly that the 957 salts of Edmondson was “a far cry from the 20 compounds ‘envisaged’ by the narrow genus in Petering.”

As to obviousness, interestingly, Merck was able to eliminate Edmondson as a reference as to claims 1 and 2 by proving prior invention and relying on the obviousness exception for commonly owned prior art of pre-AIA 35 USC 103(c). However, this approach was not effective as to claim 4, which was limited to a crystalline monohydrate of the (R)-configuration of 1:1 sitagliptin DHP.

As to claim 4, Mylan relied on Edmondson’s indication that the described salts may exist in more than one crystal structure and in the form of hydrates. Mylan further relied on the disclosure in a secondary reference of the pharmaceutical importance and prevalence of crystalline hydrates of pharmaceutical compounds.

The CAFC agreed with the PTAB and Merck that the general teachings of the secondary reference would not have led a skilled artisan to prepare a crystalline monohydrate of the (R)-configuration of 1:1 sitagliptin DHP based on the teachings of Edmondson with a reasonable expectation of success, noting the unpredictability of hydrate formation and function for specific compounds.

The Federal Circuit briefly noted the PTAB’s consideration of Merck’s evidence of unexpected results, but also noted that “there is no need to reach objective indicia of nonobviousness where the petitioner has not made a showing necessary to prevail on threshold obviousness issues.”

Takeaway: During examination, claims directed to chemical compounds and compositions are often rejected over prior art disclosing generic chemical formulae or separate lists of components. The numbers of specific compounds or compositions encompassed by such prior art can be astronomical. The Mylan case provides some tips for arguing over such rejections (preferably without the need to rely on additional experimental results). Possible arguments include identifying the large number of species encompassed by a prior art genus, emphasizing the lack of direction in the prior art toward the specific selections necessary to obtain a claimed compound or composition, and pointing out the difficulty of applying general teachings regarding selection (e.g., of substituents, subcomponents, etc.) to specific compounds or compositions.

Judges: Lourie, Reyna, Stoll



March 19, 2021by Matthew Barnet

Chemical compounds in patent claims often include variables representing different possible substituent groups. For example, a chemical formula may include a variable R1 representing a hydrogen atom or an alkyl group, a variable R2 representing an alkenyl group, and a variable X representing a halogen atom. This notation allows for a compact representation of many different specific compounds (species) within a generic formula (genus).

When evaluating a genus of chemical compounds for obviousness, U.S. examiners often find a disclosed genus of chemical compounds sharing species with the claimed genus. The question then is whether the disclosed genus of chemical compounds is sufficient to render obvious the claimed genus of compounds. This issue is illustrated in the recent Patent Trial and Appeal Board (“Board”) case of Ex parte Alig.

Independent claim 1 recited a method for controlling animal pests with an N-arylamidine substituted trifluoroethyl sulfoxide derivative of formula (I):


n represents the number 1,

X represents fluorine, chlorine, bromine, or iodine,

Y represents (C1-C4)-alkyl or (C1-C4)-haloalkyl,

R2 represents hydrogen, (C1-C4)-alkyl or (C1-C4)-haloalkyl, and

R1 and R3 together with the atoms to which they are attached represent the group

where the arrow points to the remainder of the molecule.

The examiner rejected claim 1 on the ground of non-statutory obviousness-type double patenting over claims 1-20 of U.S. Patent No. 9,642,363 (“the ‘363 patent”) in view of WO 2007/131680. As articulated by the Board, “[t]he Examiner’s position, essentially, [was] that the pending claims would have been obvious over the reference claims because the reference claims disclose a genus of compounds that encompasses the compounds recited in the pending claims.”

The applicant explained that to arrive at the compounds in the pending claims, a person of ordinary skill in the art would need to make several specific choices to narrow the genus recited in the reference claims. For example, the person would need to choose the specific ring structure formed by R1 and R3 in pending claim 1 from among 14 ring systems recited in claim 1 of the ‘363 patent and 16 groups recited in claim 8 of the ‘363 patent. Additionally, the person would need to choose fluorine, chlorine, bromine, or iodine for the variable X in pending claim 1, from among 41 substituents (many of which could contain further substitutions) in the claims of the ‘363 patent. The person also would need to choose (C1-C4)-alkyl or (C1-C4)-haloalkyl for the variable Y in pending claim 1, from among 41 substituents (many of which could contain further substitutions) in the claims of the ‘363 patent. The applicant argued that pending claim 1 was not obvious because the “claims of the ‘363 patent provide no teaching whatsoever that would suggest the specific choices that would lead to the claimed compounds.”

The Board agreed with the applicant. The Board explained that “[t]he fact that the pending claims recite compounds encompassed within the genus disclosed in the prior art is not, by itself, sufficient to establish a prima facie case of obviousness” (citing In re Baird, 16 F.3d 380 (Fed. Cir. 1994) and In re Jones, 958 F.2d 347 (Fed. Cir. 1992)). The Board noted that “[i]n both Baird and Jones, our reviewing court reversed rejections similar to the present rejection, in which the rejected compounds were encompassed by large genera that included millions of compounds, but the prior art did not suggest selecting from those genera the particular compound, or subgenus of compounds, recited in the claims at issue.”

The Board found that the examiner did not “provid[e] a sufficient evidentiary basis explaining why, out of the enormous number of possibilities encompassed within the genus described in the ‘363 patent, a skilled artisan would have made the particular set of selections and modifications that would be required to arrive at the compounds recited in the pending claims.” The Board concluded that “[t]he mere fact that one might arrive at Appellant’s claimed compounds by a hindsight-guided selection of appropriate substituents from the large genus disclosed in the reference claims does not persuade us that the pending claims would have been obvious to a skilled artisan.” Thus, the Board reversed the double patenting rejection.

Takeaway: When claims recite a sub-genus of chemical compounds, and the examiner rejects the claims as obvious over a broader genus of compounds, it is important to analyze the selections necessary to arrive at the sub-genus. If the applied references do not provide guidance for making such selections, then a strong argument can be made against obviousness.

Judges: Fredman, Cotta, Hardman


September 7, 2020by Richard Treanor

On July 14, 2020, the Patent Trial and Appeal Board issued a decision in Ex parte Park (Appeal 2019-006050) in which a rejection over an overlapping prior art genus was determined to be insufficient to establish a prima facie case of obviousness under both a lead compound analysis and an obvious equivalents/overlapping genus analysis. In addition, the Examiner’s initial rejection of subject matter beyond the elected specie was determined to be a withdrawal of the election requirement.


In assessing the obviousness of chemical species when prior art teaches an encompassing genus, Section 2144.08 of the MPEP advises us to consider any teaching or suggestion in the reference of a preferred species or subgenus that is significantly different in structure from the claimed species or subgenus—because such a teaching may weigh against selecting the claimed species or subgenus.  See M.P.E.P. § 2144.08, para. II.A.4(c).