The Markush patent claim arose as a solution to the challenging problem of describing inventions that could not be defined any other way than by a list of the members of a group. The original Markush group, claimed in 1923, listed only three alternatives; in the years since, the populations of these groups have swelled to totals beyond calculation, as pharmaceutical companies took advantage of the opportunity to claim multitudes of alternative chemical compounds by systematically iterating the functional groups at various molecular positions. However, without completing the now-impossible task of synthesizing and testing each of innumerable chemical compounds for patentable utility, how can a patent applicant realistically have fulfilled the statutory requirements to obtain a patent? Is the United States now protecting the mere ability to conceive of possible compounds that may never be synthesized or tested? As the AIA converts our patent system to a first-to-file structure, and the numbers of Markush group members threaten to bloat even more in the rush to preserve priority, we must reconsider and reform the Markush claim before the ability to invent chemical compounds becomes synonymous with the ability to conceive.
Adam Sussman, Million-Card Monte: Reforming the Markush Claim Post-AIA to Save Synthetic Chemical Innovation, 12 J. Marshall Rev. Intell. Prop. L. 720 (2013)