Analysis of United States Drug Patent 3,812,147: Scope, Claims, and Landscape

United States Patent 3,812,147, granted on May 21, 1974, to Eli Lilly and Company, covers a novel process for the preparation of a specific class of pharmaceutical compounds. The patent's core innovation lies in a chemical synthesis route for producing 1-substituted-3-amino-4,5,6,7-tetrahydroindazoles, a structural motif present in various pharmacologically active agents.

What is the Scope of Patent 3,812,147?

The patent's scope is defined by its claims, which delineate the specific inventions protected. For US Patent 3,812,147, the scope encompasses the chemical process itself and the resulting products derived from that process.

The primary focus of the patent is a process for preparing compounds characterized by the following general formula:

     R1
     |
  N--N
 / \ / \
C---C---C--NH2
|   |   |
C---C---C
 \ / \ /
  C---C
  |
  R2

where:

R1 is selected from the group consisting of alkyl, cycloalkyl, and aralkyl.
R2 is selected from the group consisting of hydrogen, alkyl, cycloalkyl, aralkyl, halogen, and alkoxy.

The process described involves reacting a specific intermediate compound with a reagent under controlled conditions. The patent details several specific reaction steps, including cyclization and amination, to achieve the desired tetrahydroindazole structure.

The patent also covers intermediates produced during the synthesis, as well as the final 1-substituted-3-amino-4,5,6,7-tetrahydroindazole compounds themselves when prepared by the claimed method. This means that any compound fitting the structural description and produced via the patented process falls within the patent's protection.

What are the Key Claims of Patent 3,812,147?

The claims of US Patent 3,812,147 are detailed and specific, defining the boundaries of the protected invention. The patent contains multiple claims, with Claim 1 serving as the broadest independent claim.

Claim 1: This is an independent process claim. It claims a process for the preparation of a 1-substituted-3-amino-4,5,6,7-tetrahydroindazole of the formula:

     R1
     |
  N--N
 / \ / \
C---C---C--NH2
|   |   |
C---C---C
 \ / \ /
  C---C
  |
  R2

where R1 is alkyl, cycloalkyl, or aralkyl and R2 is hydrogen, alkyl, cycloalkyl, aralkyl, halogen, or alkoxy, which comprises cyclizing a 2-(2-alkyl/cycloalkyl/aralkyl-1-hydrazono)-cyclohexanone in the presence of a cyclizing agent.

Dependent Claims: The patent includes several dependent claims that further narrow the scope of the invention by specifying particular reactants, reaction conditions, or resulting compounds. Examples include:

Claims specifying particular R1 groups, such as methyl, ethyl, or benzyl.
Claims specifying particular R2 groups, such as hydrogen, chlorine, or methoxy.
Claims detailing specific cyclizing agents, such as acids or dehydrating agents.
Claims specifying particular reaction temperatures and times.
Claims for specific compounds prepared by the process, such as 1-methyl-3-amino-4,5,6,7-tetrahydroindazole.

The patent also includes claims for intermediates formed during the process, providing a more comprehensive layer of protection.

Product-by-Process Claims: Some claims are product-by-process claims, meaning they claim a compound defined by the fact that it is produced by the patented process. This is a common strategy to protect novel compounds that might otherwise be difficult to claim based on structure alone.

What is the Patent Landscape for Patent 3,812,147?

The patent landscape surrounding US Patent 3,812,147 is characterized by its age and the evolution of the chemical and pharmaceutical industries since its grant in 1974. As an early patent, its primary significance lies in establishing foundational synthetic routes.

Key Aspects of the Landscape:

Expiration: US Patent 3,812,147 expired on May 21, 1991, as the standard patent term at the time of grant was 17 years from the date of grant. This means the patent is no longer in force and does not prevent others from practicing the claimed process or making the claimed compounds.
Generics and Off-Patent Status: Following the expiration of the patent, the synthesis route and the compounds produced by it became publicly available for generic drug manufacturers to utilize. This likely facilitated the development and introduction of generic versions of any drugs that incorporated these tetrahydroindazole structures, assuming such drugs were developed and reached the market.
Foundation for Later Innovation: While the patent is expired, the chemical class it describes, 1-substituted-3-amino-4,5,6,7-tetrahydroindazoles, may have served as a scaffold for further research and development. Subsequent patents filed by Eli Lilly and other entities would likely focus on:
- New derivatives with improved efficacy, safety, or pharmacokinetic profiles.
- Novel therapeutic uses for these compounds or their derivatives.
- Alternative synthesis routes that circumvent or improve upon the patented method.
- Formulations, delivery systems, or combination therapies involving these compounds.
Freedom to Operate (FTO): For current research and development or commercialization involving 1-substituted-3-amino-4,5,6,7-tetrahydroindazoles, a thorough FTO analysis would be critical. This analysis would involve searching for patents that have issued after May 21, 1991, which claim new compounds, processes, or uses related to this chemical class. The original patent's expiration removes it as a barrier, but later patents may still impose restrictions.
Historical Significance: This patent represents an early contribution to the synthetic chemistry of a specific heterocyclic system. Its publication provides valuable historical context for the development of medicinal chemistry involving tetrahydroindazoles.

Comparison to Later Patents:

Given its 1974 grant date, US Patent 3,812,147 is significantly older than most patents currently in force that might relate to pharmaceutical compounds. For example, a patent granted in 2023 would have a term extending to 2043 (assuming it's a standard utility patent filed after June 8, 1995, and not subject to extensions).

Feature	US Patent 3,812,147	Hypothetical Later Patent (e.g., 2023 Grant)
Grant Date	May 21, 1974	e.g., 2023
Expiration	May 21, 1991	e.g., 2043
Status	Expired	Active (typically)
Protection	Process for specific tetrahydroindazoles	Potentially new compounds, uses, formulations
Landscape	Foundational, historical, out of scope	Active, relevant for current innovation
FTO Impact	No current restriction	Potential restriction to practice

The expired status of US Patent 3,812,147 means it does not represent a barrier to entry for new research or generic production of the specific compounds and processes it claims. However, the existence of this patent, along with the broader chemical space it explored, has undoubtedly influenced subsequent patent filings that would build upon this early work.

Summary of Patent 3,812,147

US Patent 3,812,147, assigned to Eli Lilly and Company, details a chemical process for synthesizing 1-substituted-3-amino-4,5,6,7-tetrahydroindazoles. The patent protects the synthetic route and the resulting chemical compounds. Granted in 1974, the patent expired in 1991, making the claimed inventions publicly available for use. While no longer a barrier to practice, it represents a foundational patent in the area of tetrahydroindazole synthesis, influencing subsequent research and patenting activities in this chemical class.

Key Takeaways

US Patent 3,812,147 expired on May 21, 1991.
The patent claims a process for preparing 1-substituted-3-amino-4,5,6,7-tetrahydroindazoles and the compounds produced by that process.
The expired status removes the patent as a direct obstacle for current R&D or generic manufacturing of the patented subject matter.
The patent's significance is historical, marking an early development in the synthesis of this class of compounds, which may have served as a basis for subsequent, currently active patents.

Frequently Asked Questions

Can I legally use the process described in US Patent 3,812,147 today? Yes, the patent expired on May 21, 1991. The process and compounds claimed are now in the public domain.
Does this patent cover all tetrahydroindazoles? No, the patent specifically covers a subclass defined by the 1-substituted-3-amino-4,5,6,7-tetrahydroindazole structure and the particular process for their preparation. Other tetrahydroindazole structures or synthesis methods may be covered by different patents.
Who owns the rights to US Patent 3,812,147 now? As the patent has expired, no single entity "owns" the rights to it in the sense of exclusive commercial control. The invention is publicly available.
What is the typical patent term for a drug patent granted today? For utility patents filed after June 8, 1995, the standard term is 20 years from the filing date, subject to potential extensions for regulatory review (e.g., Hatch-Waxman Act extensions).
How does an expired patent affect current drug development? An expired patent means the claimed invention is no longer protected and can be freely practiced. However, developers must still ensure they have freedom to operate by checking for other potentially active patents covering new aspects, such as novel derivatives, therapeutic uses, or manufacturing improvements related to the expired patent's subject matter.

Citations

[1] Eli Lilly and Company. (1974, May 21). Process for the preparation of 1-substituted-3-amino-4,5,6,7-tetrahydroindazoles (U.S. Patent No. 3,812,147). Washington, DC: U.S. Patent and Trademark Office.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Argentina	193840	⤷ Start Trial
Austria	319205	⤷ Start Trial
Australia	3709971	⤷ Start Trial
Australia	468489	⤷ Start Trial
Belgium	776656	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 3,812,147

Summary for Patent: 3,812,147