Pharmaceutical Compound Nonobvious Absent Evidence Suggesting Specific Modification to Prior Art Compound

By Wanli Tang, Ph.D. and J. Patrick Elsevier, Ph.D.

The PTAB issued a final written decision in IPR2016-00204, upholding the validity of claims 1–13 of Patent RE38,551 E (“the ’551 patent”), which covers the antiepileptic drug VIMPAT® (lacosamide).

The petitioner, Argentum argued that a prior art publication by the inventor of the ’551 patent (“Kohn 1991”) identified compound 31 as a lead antiepileptic compound, and that only a single substitution of compound 31—a biosteric replacement of a methoxyamino group with a methoxymethyl group—was required to arrive at lacosamide. Argentum further argued, relying on expert testimony, that an ordinary artisan would have been motivated to make this replacement because compound 31’s methoxyamino group is an uncommon moiety among commercial pharmaceuticals that presents potential synthetic and stability issues, and the proposed substitute, a methoxymethyl group, is a more common acceptable moiety for pharmaceutically active compounds.

Although the PTAB credited Argentum’s expert’s testimony that “an ordinary artisan may have had a reason to replace [a methoxyamino group] with a more common and acceptable moiety, such as a methoxymethyl group, in chemical compounds generally,” the PTAB nonetheless found that Petitioner did not persuade it that the prior art of record would have suggested making the specific modification to compound 31 required to yield lacosamide.

The PTAB also examined the evidence submitted by the patent owner, Research Corporation Technologies, Inc. (“RCT”), supporting that “replacement of [the methoxyamino group in compound 31] with other substituents would have led to a reduction in activity,” as well as “result in a compound with a significantly different conformation and biological activity.” Assessing evidence from both sides, the PTAB found that “the weight of the evidence significantly favors [RCT’s] position,” as RCT’s evidence specifically suggests that an ordinary aritisan would have not have viewed the posited substitution as being desirable, despite Argentum’s evidence of a more general motivation to the contrary.

As such, the PTAB concluded that Argentum failed to meet its burden to establish by a preponderance of evidence that the challenged claims were obvious, because it did “not explain sufficiently why those factors would have led an ordinary artisan to modify compound 31 in the specific manner required to yield lacosamide, particularly given the evidence to the contrary.” The PTAB further found that certain objective indicia of nonobviousness proffered by RCT supported its determination.