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Obviousness Based on Structural Similarity Generally Requires "Reasoned Identification" of a Lead Compound


In Eisai Co. v. Dr. Reddy's Laboratories, Ltd. (No. 07-1397, -1398; July 21, 2008), the Federal Circuit affirms a summary judgment that a patent for rabeprazole and its salts is not invalid and is enforceable, as well as a judgment following a bench trial that the defendants had failed to prove their remaining allegations of inequitable conduct. Rabeprazole's sodium salt is the active ingredient in Aciphex, an FDA-approved drug for treating duodenal ulcers, heartburn, and associated disorders.

Where obviousness is based on structural similarity of a chemical compound, a prima facie case generally must begin with a "reasoned identification" of a known compound, i.e., a lead compound, that a person having ordinary skill in the art would have selected and modified to obtain the claimed compound. In other words, the record must contain some reason known to one with ordinary skill in the art up to the time of invention to modify the lead compound in a particular way to achieve the claimed compound. The lead compound and claimed compound in this case were largely identical in structure. The Federal Circuit agrees, however, that the record lacked any evidence of a reason why a skilled artisan would have removed the only differentiating group from the former to produce anti-ulcer action, which was characteristic of the latter.

The Federal Circuit also holds that the district court properly rejected the defendants' inequitable conduct claims. Although prudence dictates the disclosure of closely related applications, the patentee's failure to disclose its own-copending application on the "ethyl homolog" of rabeprazole did not rise to inequitable conduct. The "ethyl homolog" label was misleading: there was no evidence that the patentee's scientists ever referred to it as such or considered it in close relation to rabeprazole. The record further lacked evidence of any intent to deceive the PTO and such evidence could not be inferred from the filing of separate patent applications for the two compounds. Finally, the patentee's failure to identify to the examiner a patent application for the lead compound also did not constitute inequitable conduct: the passing comment of an insider that the similarity of the lead compound and the claimed compound bothered him did not establish materiality nor intent.


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Mark Supko
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Phone: +1 202.624.2734