Minnesota’s Claim 1 required a set of compounds having the following structure:

R₁ through R₇ are each a genus of identified compounds, with the result that the claims are broadly directed to a class of drugs, known as phosphoramidate prodrugs, that target tumor-growing viruses. Suffice it to say that given the number of R groups in these structures, the size of each genus of those R groups, and the options given elsewhere in the claims, the number of potentially infringing compounds was very broad indeed.

The filing date of the patent was March 28, 2014, but it claimed through a chain of priority back to a 2004 provisional patent. In its IPR petition, Gilead submitted that a prior art reference (Sofia), published in 2010, anticipated the claims. The parties agreed that Sofia anticipated claim 1 and all dependent claims. Therefore, the decision turned on whether Minnesota’s claim was entitled to the 2004 priority date of the provisional application (and, thus, made Sofia unavailable for use as prior art based on its later publication date). Because a patent claim must be supported by the written description of the earlier filed application in order to obtain the benefit of its filing date, Minnesota had to show that the claimed compound was adequately supported by the written description of the 2004 provisional application. (The intervening chain of priority claims through an international application and two nonprovisional applications did not materially modify the scope of the disclosure.)

From the above discussion, it would seem that this is a case of whether the genus was sufficiently described in the provisional application to permit Minnesota to claim particular species. In such cases, the Federal Circuit has held that the genus must be described by “either a representative number of members of the genus or structural features common to the members of the genus” such that a person of ordinary skill could visualize or recognize the members of the genus(see Ariad Pharms., Inc. v. Eli Lilly & Co., 598 F.3d 1336, 1350-52 (Fed. Cir. 2010) (en banc). But Minnesota did not argue that it had sufficiently disclosed a genus. Rather, it argued that it had actual support in the provisional application for the claimed set of compounds by either literally describing the claimed compounds or providing “blaze marks” to them. A blaze mark is a colored mark or signpost marking the direction of a hiking trail.

Now, a patent claim is often likened to the “metes and bounds” of a real estate deed, or the fence on a land boundary, marking off what the patentee claims as his own exclusive right. To be granted that right, the patentee must also sufficiently describe the invention and its context within the art to demonstrate his possession of the inventive concept. This is like describing the landscape within the borders of the fence. By blaze marks, then, the parties, PTAB, and Federal Circuit mean that the patentee cannot merely run off an exhaustive list of every subcompound that might conceivably be used with the claimed genus, as if naming every tree in the Minnesota Northwoods property that has been purchased. Something more is required: blaze marks directing the artisan to that particular claimed compound, or that particular tree in the woods, such that the artisan can have a reasonable belief that the person making the patent claim actually recognized it as part of the invention.

Returning to the case, the Federal Circuit affirmed the PTAB’s finding that Minnesota failed to make the necessary disclosures in the provisional application to provide that reasonable belief. First, the Federal Circuit rejected Minnesota’s argument that the claimed compounds were literally described in the provisional application. Minnesota relied on the fact that claim 47 in the provisional application, which claimed “the compound of any one of claims 1-46” wherein R₇ was a relevant compound (hydrogen or a particular alkyl group), was the literal equivalent of claim 1 of the later filed 2014 patent. The problem, according to the Federal Circuit, was that the number of dependent claims and the “maze-like path” between them gave no assurance that the inventor recognized in 2005 what the patent claimed in 2014 as being particularly inventive.

Minnesota then claimed that even if this was not a literal description, the claim path did provide the necessary blaze marks. Again, the Federal Circuit disagreed, finding that “even if…. claim 47 blazes a trail through the forest that runs close by the later-claimed tree, the priority applications do not direct one to the proposed tree in particular, and do not teach the point at which one should leave the trail to find it.” The Federal Circuit then affirmed the decision to invalidate the Minnesota patent.

This case is important for patentees and patent lawyers for two reasons. First, it continues a trend dating back about 10-15 years whereby the Federal Circuit has required patentees to be more explicit in the specification about the nature of the inventor’s conception of the invention. It is not enough to describe a small number of compounds and then claim a large genus, or alternatively, to rattle off every potential hypothetical compound to try to support a large genus claim. Rather, the Federal Circuit wants to see that the disclosure reflects what the inventor believed to be his invention. While this case involves the written description requirement of Section 112, it is similar to an analogous question about the enablement requirement currently before the Supreme Court in Amgen, Inc. v. Sanofi. The courts want to see what the inventor knew and when he knew it.

This leads to the second point. Minnesota filed the original provisional application in 2004, and the patent in issue was filed 10 years later. The intervening prior art was only published in 2010. Therefore, if there are questions about the sufficiency of the disclosure, it may be worthwhile to file a new patent application with additional disclosure (either as a completely new case or as a continuation in part application) directing the Office to the particularly desired inventive concepts. Had Minnesota filed an adequately supported patent claim any time between 2004 and 2010, it likely would have survived this challenge.

The Federal Circuit’s trend towards requiring more of patent disclosures is not likely to be reversed any time soon. That means that inventors who are blazing trails in their respective technical fields need to make sure to leave enough marks in their patent disclosures for others to follow behind.