Claiming a Compound: Markush Groups, Ranges, and the Chemistry of Patent Scope
By Casey Scott McKay ·
Chemical and materials inventions are claimed in a language of genus and species that no other field uses, and the whole of their commercial value turns on how much of that genus a court will let the patentee keep. This article works through Markush practice, the enablement and written description limits the Supreme Court restated in the antibody context and that apply with equal force to chemistry, and the obviousness analysis that treats structural similarity as a presumption to be rebutted by unexpected results. It then covers ranges and criticality, polymorphs and salt forms, product-by-process claiming, and inherent anticipation. The second half turns to the choice between patenting and secrecy, which in chemistry is decided by analytical chemistry rather than by doctrine, and to the regulatory filings that can destroy secrecy without anyone intending it. It closes on freedom to operate, where broad Markush claims make clearance uniquely difficult.
IP and Technology > Patent Counseling Transactions | Article | Published 3 January 2024 - Updated 6 July 2025 | Casey Scott McKay - marksy.us
Summary. Chemical and materials inventions are claimed in a language of genus and species that no other field uses, and the whole of their commercial value turns on how much of that genus a court will let the patentee keep. This article works through Markush practice, the enablement and written description limits the Supreme Court restated in the antibody context and that apply with equal force to chemistry, and the obviousness analysis that treats structural similarity as a presumption to be rebutted by unexpected results. It then covers ranges and criticality, polymorphs and salt forms, product-by-process claiming, and inherent anticipation. The second half turns to the choice between patenting and secrecy, which in chemistry is decided by analytical chemistry rather than by doctrine, and to the regulatory filings that can destroy secrecy without anyone intending it. It closes on freedom to operate, where broad Markush claims make clearance uniquely difficult.
Keywords: chemical patents · Markush claims · genus and species · enablement · written description · unexpected results · lead compound analysis · overlapping ranges · criticality · polymorphs and salts · product-by-process claims · inherent anticipation · formulation trade secrets · analytical reverse engineering · TSCA confidential business information · safety data sheets · freedom to operate in chemistry · selection inventions · doctrine of equivalents · prosecution history estoppel
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