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The Obviousness of Chemical Compounds in Patent Applications

A patentable invention is an invention that is “novel” under 35 U.S.C.A. § 102, “useful” under 35 U.S.C.A. § 101, and “nonobvious” under 35 U.S.C.A. § 103. Section 103(a) of the Patent Act sets forth the parameter of the obviousness requirement:

A patent may not be obtained though the invention is not identically disclosed or described as set forth in Section 102 of this title, if the differences between the subject matter sought to be patented and the prior art must not be such that the subject matter as a whole would have been obvious at the time the invention was made to a person having ordinary skill in the art to which said subject matter pertains.

In Graham v. John Deere Co., 383 U.S. 1, 17 (1966), the United States Supreme Court interpreted this language to mean that the ultimate determination on the issue of obviousness is treated as a question of law but is based on factual inquires that include (1) the scope and content of the prior art; (2) the differences between the prior art and the claimed invention; (3) the level of skill in the art; and (4) the objective evidence of non-obviousness.

To obtain a patent on a new chemical compound, the compound must meet the nonobviousness requirement at the time it is invented. Special issues, however, arise with chemical patents because unlike electrical and mechanical sciences, chemistry is an unpredictable art. Minor changes in structures can dramatically affect a compound's properties. Thus, it is inherently difficult for a court to determine the obviousness of a claimed compound with a similar structure to that of a prior art.

The extent of the challenge to determine the obviousness of chemical compounds can be illustrated by the issues faced by the court in Yamanouchi Pharmaceutical Co. v. Danbury Pharmacal, 231 F.3d 1339 (Fed. Cir. 2000). In Yamanouchi, the dispute centered on whether one skilled in the art would have considered it obvious to make the drug Famotidine by (1) combining the polar tail from lead compound 44 with the modified heterocycle from Tiotidine to form an intermediate compound, and (2) substituting the carbamoyl group in the intermediate compound with a sulfamoyl group to create Famotidine as shown below in Scheme 1. It was well known that both Tiotidine and Tagamet were prior compounds, of which Tagamet was a successful drug in market place while Tiotidine failed in preclinical trials due to its high toxicity. Both compounds, however, showed high efficacy as inhibitors of gastric acid secretion.

The court in Yamanouchi upheld the patent against an assertion of obviousness. Id. at 1345. The court explained, “For a chemical compound, a prima facie case of obviousness requires a showing of ‘structural similarity between claimed and prior art subject matter … where the prior art gives reason or motivation to make the claimed compositions.’” Id. at 1343 (quoting In re Dillon, 919 F.3d 688, 692 (Fed. Cir. 1990)). Even though the claimed compound failed the test of structural similarity, the Yamanouchi court invalidated a prima facie case of obviousness based on a lack of motivation to combine the prior art to make the claimed invention with similar biological function to that of the prior art.

A. Structural similarity

Structural similarity between chemical compounds has effectively created a unique and troublesome area of patent law. In re Jones, 958 F.2d 347, 350 (Fed. Cir. 1992). In determining the obviousness of a traditional chemical compound, courts previously focused on the similarity between the structures of a claimed compound and that of a compound disclosed in the prior art. In re Hass, 141 F.2d 122 (C.C.P.A 1944); In re Henze, 181 F.2d 196 (C.C.P.A. 1950).

In Hass, the claimed compound was a homolog of a prior art compound (Scheme 2). See Hass, 141 F.2d at 125. There was only one more carbon unit in the claimed compound than that in the prior art. The Court of Claims and Patent Appeals held that the claimed compound was not patentable unless it revealed “some nonobvious or unexpected beneficial properties not possessed by the homologous compound disclosed in the prior art.” Id. The general principle behind the court’s decision was that chemical and physical properties vary only slightly between members of a homologous series. Id. The Henze case transformed this principle into a presumption that was rebuttable if the applicant showed “that the claimed compound possesses unobvious or unexpected beneficial properties not actually possessed by the prior art homologues.” In re Henze, 181 F.2d at 201. Clearly both courts perceived chemical structure and chemical properties as two different considerations. Therefore, for structurally similar chemical homologues, a new compound was deemed prima facie obvious because a chemist could expect or predict that the new chemical compound would have the same properties in a given system as did a similar prior art compound.

B. Inseparable structure and its properties

After section 103 was enacted, courts gradually moved to a more holistic view of chemical compounds that considered chemical properties in addition to chemical structures. In re Papesch, 315 F.2d 381 (C.C.P.A. 1971). In ­Papesch, an applicant claimed a family of compounds including representative compound 2,4,6-triethylpyrazolo(4,3-d)-4,5,6,7-tetrahydropyrimidine-5,7-dione (ethyl = CH2CH3), which was admittedly “structurally obvious” in light of a claimed compound 2,4,6-trimethylpyrazolo(4,3-d)-4,5,6.7-tetrahydropyrimidine-5,7-dione (methyl = CH3) as shown in Scheme 3. Id. at 384.

Comparative tests of the trimethyl compound and the applicant’s triethyl compound showed that the latter was an active anti-inflammatory agent while the prior art compound was completely inactive for that utility. The Papesch court stated that the properties of compounds were relevant to obviousness, emphasizing that the invention as a whole was a compound with its own properties. Id. at 390. Additionally, the court found that proof of non-obvious or unexpectedly advantageous properties not shared by the prior art compound may rebut a prima facie case of obviousness. Id. at 391.

A compound and all of its properties are inseparable; they are one and the same thing …. But a formula is not a compound and while it may serve in a claim to identity what is being patented, as the metes and bounds of a deed identify a plot of land, the thing that is patented is not the formula but the compound identified by it. And the patentability of the thing does not depend on the similarity of its formula to that of another compound but of the similarity of the former compound to the latter. There is no basis in law for ignoring any property in making such a comparison. Id.

Thus the court generously encouraged chemical patent applications as long as a claimed invention could demonstrate new properties even though the claimed compound shared a similar structure with a prior art compound. The Papesch court, however, did not deal with the requirements for establishing a prima facie case of obviousness. The court only held that, for cases with a presumption of obviousness, an examiner had to consider both the properties of the invention and the structural similarity. Id.

About the Author: Michael Guth is a legal editor who helps polish legal drafting by other attorneys. While in law school, he won an award for having the best brief written by a first-year law school student. He can be reached through the email link on web page

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