Since I’ve been practicing chemical patent law, I’ve always been taught that a new chemical compound is prima facie obvious over an old compound when the new and old compounds are homologs. Thus, if the new compound includes a methyl where the old compound included a hydrogen, an examiner would refuse to allow a claim to the new compound without an experimental comparison of the two compounds, and evidence of unexpected results. Examiners have been applying this logic for years based on the presumption that homologs will have similar properties, and the following language from section 2144.09 of the Manual of Patent Examining Procedure:
“A prima facie case of obviousness may be made when chemical compounds have very close structural similarities and similar utilities. An obviousness rejection based on similarity in chemical structure and function entails the motivation of one skilled in the art to make a claimed compound, in the expectation that compounds similar in structure will have similar properties. In re Payne, 606 F.2d 303, 313, 203 USPQ 245, 254 (CCPA 1979).”
That simple logic took a hit recently at the Patent Trial and Appeals Board (“Board”) in In re Remick, 2017 Pat. App. LEXIS 12839 (P.T.A.B. Dec. 28, 2017), based on the Federal Circuit’s lead compound analysis. The lead compound analysis has been applied by the courts since at least the Federal Circuit’s 2007 decision in Takeda Chem. Indus., Ltd. v. Alphapharm Pty., Ltd., 492 F.3d 1350, 1357 (Fed. Cir. 2007). Under the lead compound analysis, an old compound can serve as the basis for an obviousness finding only if the old compound was a natural choice for further development. As explained by the Board:
“A lead compound is defined as a compound in the prior art that would be most promising to modify in order to improve upon its . . . activity and obtain a compound with better activity. Otsuka Pharm. Co., Ltd. v. Sandoz, Inc., 678 F.3d 1280, 1291 (Fed. Cir. 2012). Stated another way, a lead compound is a natural choice for further development efforts. Id.”
In In re Remick, the prior art homolog (“compound 280”) was described in an earlier patent (the “Suzuki” patent) alongside 286 other compounds, but it had no data to support it. According to the Board:
“Suzuki provides IC50 data for 176 of the 286 exemplified compounds, but not for compound 280. … Suzuki does not identify compound 280 as a preferred compound, highlight compound 280, or otherwise indicate that compound 280 provides any ‘benefit or special property’ as compared to any of the other compounds disclosed. [No] biological data is provided for compound 280.”
In other words, compound 280 was not the most promising compound to modify in the Suzuki patent, or a natural choice for further development. Because compound 280 was not a natural choice fo further development, a worker of ordinary skill would not have been motivated to modify compound 280 to arrive at Remick's homolog, and the Suzuki patent did not render Remick’s methyl homolog prima facie obvious. The Board reversed the Examiner’s rejection.