Chemical Patents and the Limitation of Markush Structures

Chemical patents tend to utilize Markush structures as illustrations and guidelines for chemical patents. There are limitations in the industry that deserve evaluation.

Attribution

Person Holding Laboratory Flask by Chokniti Khongchum on Pexels

Chemical patents hold an interesting place when backlit by patent law as it is known. They walk a thin line between scientific and technical patents, depending on the form they take and the purpose they serve. There is also a distinction to be made between a mixture, a compound, and an element with respect to chemistry and chemical applications. Elements are of a singular material that is considered a fundamental building block, composed of one type of atom which generally have the same relative number of protons and electrons (distinctions made for isotopes and other general uniformity questions). Elements, as a matter of law, are not patentable, as it falls under the qualification of “natural phenomena.” 

Compounds, while technically different from elements in that they are composed of one or more elements and therefore, atoms, are slightly more complicated. Compounds with naturally occurring counterparts will likely not receive patent consideration, as they are within the realm of natural phenomena. 

A second class of compound is more analogous, legally, with mixtures. The fundamental difference, chemically, is best analogized with the construction of a metaphoric house. While elements would best be represented by a log cabin, with uniform construction of material, and unaltered, raw material. Simpler compounds (of which all could be considered under the umbrella of natural phenomena) could be illustrated as a house composed of composite wood planks. While between planks there may be uniformity, within each individual piece, there exists multiple materials. This is a simple distinction and though it is a step up from the complexity of a log cabin, is still relatively rudimentary in its construction. This second class of compounds lends itself well to a composite brick. Here, there lay multiple types of stone, concrete, sediments, water, and so on and so forth. This complexity is enamored within each of these uniform composite bricks and outwardly, still demonstrates a uniformity, albeit within a more complex framework on a unit by unit basis. Mixtures take this composite brick a step further, where the house might be composed of several types of composite brick, with numerous types of brick, all of which have family members that are of the same composition, but where some classes of brick vary greatly from another, all within the same construction of a house, working with the non uniform array of bricks towards the common goal of house construction. 

Mixtures are also patentable, and subject to the same test. Mixtures of a few separate building blocks (compounds or elements) can be patented, so long as the proportions of compositions are not mimicked in nature. So long as there is a uniqueness to this measurement, their patenting is generally permissible.

The second class of compounds, as well as mixtures, become harder to define and thus, patentable. The existing challenges with respect to these two questions are: “how far can one take this patentability of a material, and where is the line drawn?” The problem at hand has a wide breadth, and a good example of this is the Markush problem, where compounds are patented, but with a “plug and play” style. In compounds, there are places where different atoms and compounds can find themselves interchangeable, and at these sites they are commonly referred to as “substituents.” In the Markush problem, for example, there can be six substituated sites (denoted Rn, Where n = the position number) where R6 allows for a wide range of substituents, while R1-R5may be single atom sites. Some of which are not particularly relevant to the same industry as others, but are patented nonetheless. The question created by these challenges is at what point are these sites still a function of the patent that a foreseeable structure still fall under the purview of the patent, and when can these be enforced should another claim to the patent arise. Markush representation in patents deserve evaluation, as of now, they create a broad interpretation that can stifle scientific innovation by creating patents that unintentionally limit fields of chemistry beyond what is permissible or even intended.

Figure 1 by Joe Rios

Figure 2 by John Trombley © Creative Commons Attribution 4.0 used with permission