Implicit in a rejection for obviousness based on similarity of structure to prior art structures is the assumption that close chemical structures should have similar chemical properties such that a change in a chemical structure should yield a some what predictable result, the smaller the change, the more similar the expected molecular properties. In an absolutely predictable art, one might be able to calculate the effect that a given change will have on the function or performance of the object or material being modified, for example, an increase in serial resistance in an electrical circuit yields a proportionate decrease in current. Therefore, a prior art disclosure of an electrical circuit might render a later claimed circuit obvious where the only thing that was changed in the claimed circuit was the resistance, where that change would be expected to yield a highly predictable result. In contrast, an art that is highly unpredictable would make the predicted effect of any given change less obvious. We have already been introduced to the notion in chemical patent law that compounds that are similar in structure are predicted to have similar properties; this is the core basis for aprima facie obviousness challenge on similar structures. Assuming the prior art disclosed a meaningful utility for the disclosed structures, one of ordinary skill in the art ismotivated to make close structural analogs to make additional active compounds. However, chemistry-related arts are often unpredictable due to the fact that small modifications in a molecule’s structure or components of a composition can very often lead to large and unpredictable changes in the molecule or composition’s function .Notice a contradiction here? If not a contradiction, clearly these two principles are in tension to each other.

How can this tension be reconciled? First, it’s clear that a more nuanced approach is necessary. In this regard, it is always preferable to refer more specifically to the predictability (or lack there of) where enough is known about the particular chemical subject matter being discussed. For example, it is often the case that a class of drugs are known to relate to their target receptor or enzyme in a particular way.It may be understood in the art that certain areas of the compound can be varied considerably without greatly affecting compound activity, whereas other areas of the compound may be highly sensitive to small structural changes. A PHOSITA would expect the variation in the less critical region to yield compounds possessing the priorart disclosed activity whereas the changes in the critical or sensitive area would be less predictable since the art taught that even small variations could lead to inactive compounds. In real-world patent prosecution, the more nuanced analysis will often

An azatetracyclic compound formula

FIGURE :Claimed azatetracycle.

be offered and explained by the patent applicants themselves since they will be most familiar with the prior art and also because they will be advocating their position. For example, a patent office examiner might allege that a claimed structure is prima facie obvious and will point to the structural similarities between the claimed compound or genus and the structure(s) disclosed in the prior art. The applicants may then argue that the specific art the examiner is relying on is actually highly unpredictable and may point to additional teaching in that or other references that support their assertion.
To see how the specific un predictability of the art can argue in favor of non obviousness,consider a case heard before the USPTO Board of Appeals that dealt with this issue. Ex parte Blattnerconcerns a set of claims that were rejected by an examiner at the USPTO. The rejected claims were subsequently appealed to the Board. The claimed subject matter in dispute concerned compound claims and methods directed to a set of azatetracyclic compounds for which the abbreviated claim 17, shown in Figure above , was considered representative. Additional claims were directed to various structural sub embodiments and pharmaceutical compositions containing the compounds of the invention as well as particular methods of use of the compounds including the treatment of agitation in a mammal.
The examiner rejected applicant’s claimed invention for obviousness, citing U.S.4,002,632 (the ’632 patent), which was prior art to applicant’s claimed invention and disclosed the genus in Figure above as having antide pressant activity.

Claimed azatetracycle.

FIGURE : Prior art genus from ’632 patent reference having described antide pressant activity.

The prior art genus differs primarily from applicant’s claimed genus by virtue of the fused six-membered piperidine ring instead of the fused seven-membered homopiperidinering claimed by the applicant. The ’632 reference further discussed the surprising finding that their piperidine-fused compounds demonstrated antidepressant activity in pharmacological assays whereas five-membered pyrrolidine-fused compounds had depressive effects in those same assays. Thus the prior art taught that going from the five-member pyrrolidine-fused ring to the six-member piperidine-fused ring caused the activity to switch from depressive to anti depressive activity. The examiner, by asserting that the claimed genus disclosed in U.S. 4,002,632 rendered the applicant’s later claimed genus prima facie obvious was relying on the axiom that similar structures should result in similar activities. While this might be persuasive in the absence of additional information, the prior art cited by the examiner actually indicated that a small structural change in the exact same area of the compound that was the source of the difference between the applicant’s claimed invention and the genus cited against it resulted in a complete reversal in the compound’s functional activity. If a five-membered ring and a six-membered ring resulted in compounds with very different activities, what would one predict for a seven-membered ring? While the examiner wished to rely on a generality regarding the structural similarity of six- and seven-membered, nitrogen-containing ring structures, the Board was more persuaded by the specific unpredictability demonstrated by the very art that the examiner used to support his argument. As a result, the Board overruled the examiner, and the claims were allowed.

What is worth appreciating here is that the Board of Appeals was not looking at the activity of applicant’s claimed compounds. This was not a case in which the properties of the claimed compounds were being used to demonstrate a surprising or unexpected result. Rather, this decision by the Board was specifically focused on the motivation to modify prior art compounds. The actual activity of the claimed compounds was not relevant to the Board’s decision, as they believed that the motivation to make the applicant’s claimed genus was absent from the prior art given the cited unpredictability in the art, specifically with respect to a change in the modified region of the compound’s structure. As the Board put it when rejecting the examiner’s finding: “What motivation would a person of ordinary skill in the art have expected for the azepine or 7-membered ring compound? A tranquilizer?An anti-depressant?
A compound which is neither because the depressant and anti-depressant effects counteract each other?” The Board’s pointed questions on this point are very important as they help sharpen our own understanding of what motivation means. When we use the term motivation in the obviousness/patentability sense, we are referring to a specific motivation to make that compound or that genus with the reasonable expectation that such a change will be successful. In the instant case, one could see a general motivation to make additional homologues to explore what effect the change might have on the compound’s activity. However, since the art already teaches that as mall change could lead to a very different activity, one would not have the specific motivation necessary to pursue any of the utilities alleged in the literature as any number of activities (or none at all) could be the result.

Finally we should not confuse the motivation issue in this case with the previous discussion of In re Dillon. Recall that for In re Dillon, the applicant filed a claim for a composition comprising a hydrocarbon fuel with a tetra-orthoester, with the motivation being to reduce particulate emissions. Prior art taught compositions of hydrocarbon fuel with tri-orthoesters for de watering fuels, and also taught the equivalence oftri-orthoesters and tetra-orthoesters for de watering hydraulic fluids. In Dillon, the Board held that there was a reasonable expectation that the tri-orthoesters and tetra-orthoesters would behave similarly in hydrocarbon fuels as well. So the priorart “provided the motivation to make the claimed compositions in the expectation that they would have similar properties.” In Ex parte Blattner, no such equivalence was taught, in fact, the prior art taught that a small change in ring size could greatly change the activity of the compound, thus making the results of additional modifications to the ring size unpredictable.

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