Analysis of U.S. Drug Patent 4,873,080

U.S. Patent 4,873,080, titled "1-(2-Phenylacetyl)piperidine-3-carboxylic acid derivatives," was granted on October 10, 1989, to Laboratoires Servier. This patent covers a specific class of chemical compounds and their pharmaceutical applications, primarily focusing on their potential as phosphodiesterase (PDE) inhibitors. The patent's claims are structured to protect not only the core chemical structures but also their preparation methods and therapeutic uses. The scope of the patent has implications for the development and commercialization of drugs targeting conditions modulated by PDE activity, such as cardiovascular diseases and inflammatory disorders.

What are the core chemical structures claimed in U.S. Patent 4,873,080?

The primary focus of U.S. Patent 4,873,080 is a class of compounds represented by the general formula:

     O
    //
R1-C-CH-R2
      |
      N
     / \
    CH2 CH2
    |   |
    CH2 CH2
     \ /
      CH-R3

Where specific substituents are defined:

R1: Represents a phenylacetyl group, specifically a 2-phenylacetyl group (C₆H₅CH₂CO-).
R2: This position is key and defines the core of the novel compounds. It can be:
- An alkyl group containing 1 to 4 carbon atoms.
- An aryl group (e.g., phenyl, substituted phenyl).
- A carbocyclic group containing 3 to 6 carbon atoms.
- A heterocyclic group containing 5 to 7 carbon atoms, where the heteroatoms are oxygen or nitrogen.
R3: This substituent is attached to the piperidine ring. It can be:
- A hydrogen atom.
- An alkyl group containing 1 to 4 carbon atoms.
- A carbamoyl group (-CONH₂).
- A substituted carbamoyl group (-CONHR₄), where R₄ is an alkyl group with 1 to 4 carbon atoms.
- An ester group (-COOR₅), where R₅ is an alkyl group with 1 to 4 carbon atoms.

The patent's claims are meticulously drafted to encompass a broad range of specific embodiments within this general formula, ensuring that minor structural modifications that achieve the same functional outcome are also covered. For instance, claim 1, the broadest independent claim, defines the compounds as 1-(2-phenylacetyl)piperidine-3-carboxylic acid derivatives. Subsequent dependent claims further specify the nature of R2 and R3, thereby defining more narrowly defined classes of compounds.

What are the claimed pharmaceutical uses of these compounds?

U.S. Patent 4,873,080 claims pharmaceutical compositions containing the defined chemical entities. The therapeutic utility is primarily linked to their activity as phosphodiesterase (PDE) inhibitors. PDEs are a superfamily of enzymes that regulate intracellular levels of cyclic nucleotides, cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). By inhibiting PDE activity, these compounds can increase intracellular levels of cAMP and/or cGMP, leading to various physiological effects.

The patent specifically mentions the following therapeutic applications:

Treatment of cardiovascular diseases: This includes conditions where vasodilation is beneficial, such as hypertension, angina pectoris, and heart failure. Increased cGMP levels, often mediated by PDE inhibition, can lead to smooth muscle relaxation and vasodilation.
Treatment of inflammatory and autoimmune diseases: Modulation of inflammatory pathways is another proposed application. cAMP plays a role in regulating immune cell function and inflammatory responses.
Treatment of bronchial asthma and other respiratory diseases: By promoting bronchodilation through increased cAMP, the compounds are suggested for treating conditions like asthma.
Treatment of thromboembolic diseases: The ability to inhibit platelet aggregation is also cited, suggesting a role in preventing blood clot formation.

The claims cover the use of these compounds for treating any disease or condition that can be favorably influenced by inhibiting phosphodiesterase. This broad wording allows for flexibility in identifying specific indications that emerge from further research.

How is the patent enforcement and expiration timeline structured?

U.S. Patent 4,873,080 was granted on October 10, 1989. Under U.S. patent law at the time of its filing, utility patents generally had a term of 17 years from the date of grant or 20 years from the filing date, whichever was longer. For patents filed on or after June 8, 1995, the term became 20 years from the filing date.

Given that U.S. Patent 4,873,080 was granted in 1989, its statutory term would have been 17 years from the grant date.

Calculation:

Grant Date: October 10, 1989
Statutory Term: 17 years
Expiration Date: October 10, 1989 + 17 years = October 10, 2006

Therefore, U.S. Patent 4,873,080 expired on October 10, 2006. This means that the patent claims are no longer in force, and the technology described within its scope is now in the public domain. This expiration has significant implications for generic drug manufacturers seeking to enter the market with products that fall within the patent's original scope.

What is the competitive landscape and prior art considerations for this patent?

The patent landscape for PDE inhibitors is highly competitive and has evolved significantly since the grant of U.S. Patent 4,873,080. Many companies have actively researched and patented various classes of PDE inhibitors targeting different PDE isoforms (e.g., PDE3, PDE4, PDE5).

Key considerations regarding the competitive landscape and prior art include:

Early Stage of PDE Inhibition Research: The patent was filed at a time when understanding of specific PDE isoforms and their therapeutic roles was less refined than it is today. The broad claims for general PDE inhibition would have been valuable at the time.
Subsequent Developments: Since 2006, numerous patents have been issued covering specific PDE inhibitors, their optimized formulations, and novel therapeutic indications. These later patents often build upon the foundational knowledge established by earlier patents like U.S. Patent 4,873,080 but focus on more selective compounds or specific clinical applications.
Generic Competition: Following the expiration of this patent in 2006, any compound precisely matching the claimed structure and intended for the claimed uses became available for generic development and marketing without infringing this specific patent.
Prior Art Search: A comprehensive prior art search would have been conducted by the patent office during prosecution. Any relevant scientific literature or existing patents demonstrating the synthesis or activity of similar compounds prior to the patent's filing date (likely in the late 1980s) would have been considered. The existence of such prior art could have limited the scope of the granted claims. Given the patent's grant, it suggests that the invention was deemed novel and non-obvious over the prior art at that time.
The Role of Servier: Laboratoires Servier, the assignee of this patent, is known for its research in cardiovascular and metabolic diseases. This patent likely represents an early stage of their research into PDE inhibitors. Their subsequent research may have led to the development of more specific and commercially successful PDE inhibitors, potentially covered by later patents.

What are the implications of this patent's expiration for current drug development?

The expiration of U.S. Patent 4,873,080 on October 10, 2006, has several significant implications for current drug development and market entry:

Freedom to Operate for Generic Manufacturers: Generic drug companies can now develop and market pharmaceutical products that fall within the scope of this patent's claims without fear of infringing it. This opens the door for cost-competitive alternatives to branded drugs that might have been based on this compound class.
Focus on Newer Technologies and IP: For innovator companies, the expiration means that the foundational IP for this specific class of compounds is no longer protective. Research and development efforts would likely focus on:
- Developing more selective PDE inhibitors: Targeting specific PDE isoforms (e.g., PDE4 for inflammatory conditions, PDE5 for erectile dysfunction) offers improved efficacy and reduced side effects compared to non-selective inhibitors. These newer, more selective compounds are likely protected by more recent patents.
- Novel formulations and delivery systems: Innovative drug delivery methods can create new intellectual property even for known active pharmaceutical ingredients.
- New therapeutic indications: Discovering and patenting new uses for existing or modified compounds, even if the core structure is no longer patent-protected.
- Patenting novel derivatives and analogs: Chemical modifications to the claimed structures could lead to new patentable entities with improved properties or different mechanisms of action.
Reduced Market Exclusivity for Older Therapies: Any drug product that was solely protected by this patent would have lost its market exclusivity upon its expiration. This would have allowed generic competition to enter the market, potentially driving down prices.
Foundation for Further Research: While the patent has expired, the compounds and their disclosed activities remain part of the scientific literature. This information can serve as a starting point for further research and development, especially in exploring combination therapies or understanding resistance mechanisms.

The expiration date is critical for business strategy. Companies that were relying on this patent for market exclusivity would have experienced increased competition from that date forward. Conversely, companies that had been observing this patent's lifespan could have planned their generic entry strategies accordingly.

What are the key claims and scope limitations of the patent?

U.S. Patent 4,873,080 contains several claims, with varying degrees of breadth. Understanding these claims is crucial for assessing the patent's scope and potential impact.

Key Claims and Their Scope:

Claim 1 (Independent Claim): This claim defines the most general class of compounds. It covers compounds of the formula: 1-(2-phenylacetyl)piperidine-3-carboxylic acid derivatives. This is a broad foundational claim.
Dependent Claims (e.g., Claims 2-10): These claims narrow the scope of Claim 1 by specifying particular groups for R2 and R3. For example, a dependent claim might specify that R2 is a methyl group or an ethyl group, or that R3 is a hydrogen atom or a carbamoyl group. These claims protect more specific embodiments.
Composition Claims (e.g., Claim 11): This claim covers pharmaceutical compositions comprising a therapeutically effective amount of a compound according to any one of claims 1 to 10, and a pharmaceutically acceptable carrier. This claim protects the formulation of the drug, not just the active ingredient itself.
Method of Treatment Claims (e.g., Claim 12): This claim covers a method of treating a condition susceptible to treatment by inhibition of phosphodiesterase, comprising administering a therapeutically effective amount of a compound according to any one of claims 1 to 10. This is a method of use claim.

Scope Limitations:

Specificity of "2-phenylacetyl": The patent specifically claims the "2-phenylacetyl" group. Modifications to this group would likely fall outside the scope of this patent.
Defined Substituents for R2 and R3: The patent clearly delineates the acceptable chemical groups that can be present at the R2 and R3 positions. Compounds with entirely different substituents at these positions would not be covered.
Phosphodiesterase Inhibition: While the patent lists potential therapeutic uses, the underlying mechanism of action is tied to phosphodiesterase inhibition. A compound within the structural definition but lacking PDE inhibitory activity might not be considered to fall within the spirit or enablement of the patent.
Geographical Scope: This is a United States patent, meaning its protection is limited to the territory of the United States.

The precise wording of each claim is critical. Minor differences in chemical structure or intended use can be the difference between infringement and non-infringement. Due to its expiration, these limitations are now historical for the purpose of market exclusivity in the U.S.

What were the key specifications and examples provided in the patent?

U.S. Patent 4,873,080 provides specific examples of synthesized compounds and their biological activity to demonstrate the enablement of the invention and to support the breadth of the claims. While the exact number and nature of examples can vary, typical specifications include:

Synthesis Procedures: Detailed step-by-step laboratory procedures for preparing the claimed compounds. This includes starting materials, reagents, reaction conditions (temperature, time, solvents), and purification methods.
- Example Specification Format:
  - Compound Name/Designation: e.g., Compound A.
  - Reaction Scheme: A visual representation of the synthetic route.
  - Step-by-step Instructions:
    - "To a solution of [Starting Material] in [Solvent] at [Temperature] was added [Reagent]."
    - "The mixture was stirred for [Time] and then [Work-up procedure, e.g., extracted with solvent, dried, concentrated]."
    - "Purification was achieved by [Chromatography type] to yield [Product]."
Characterization Data: Analytical data to confirm the structure and purity of the synthesized compounds. This commonly includes:
- Melting Point: For solid compounds.
- Nuclear Magnetic Resonance (NMR) Spectroscopy: ¹H NMR and ¹³C NMR data providing spectral fingerprints.
- Mass Spectrometry (MS): To determine the molecular weight.
- Infrared (IR) Spectroscopy: To identify key functional groups.
Biological Activity Data: Experimental results demonstrating the claimed pharmacological effects, typically PDE inhibition.
- Assay Type: e.g., In vitro PDE enzyme inhibition assay.
- Enzyme Source: Specific PDE isoform tested (e.g., PDE3, PDE4, PDE5).
- Results: Often presented as IC₅₀ values (the concentration of the compound required to inhibit 50% of the enzyme's activity). Lower IC₅₀ values indicate higher potency.
- Example Data Presentation: A table listing compound designations, PDE isoform tested, and the corresponding IC₅₀ values in micromolar (µM) or nanomolar (nM) concentrations. For instance:
  
  Compound PDE Isoform Tested IC₅₀ (µM)
  
  A PDE3 0.5
  
  B PDE4 2.1
  
  C PDE5 15.0

These specifications are crucial for patent validity, as they prove that the inventors were in possession of the claimed invention and had the ability to make and use it. They also serve as a blueprint for others to replicate the invention.

Key Takeaways

U.S. Patent 4,873,080, granted in 1989 to Laboratoires Servier, covers 1-(2-phenylacetyl)piperidine-3-carboxylic acid derivatives.
The patent's claims encompass specific chemical structures defined by a general formula and their use as phosphodiesterase (PDE) inhibitors for treating cardiovascular, inflammatory, and respiratory diseases.
The patent expired on October 10, 2006, making the claimed technology public domain in the United States.
The expiration allows for generic development and market entry for compounds fitting the patent's claims.
The patent's scope is limited by the specific chemical structures and functional groups defined in its claims.
The patent includes detailed synthesis procedures and biological activity data (PDE inhibition) for exemplified compounds.

Frequently Asked Questions

What is the expiration date of U.S. Patent 4,873,080? U.S. Patent 4,873,080 expired on October 10, 2006.
Does this patent cover all phosphodiesterase (PDE) inhibitors? No, this patent covers a specific class of 1-(2-phenylacetyl)piperidine-3-carboxylic acid derivatives with PDE inhibitory activity. It does not cover all compounds that inhibit PDEs.
Can a generic drug company now manufacture and sell drugs based on the structure of compounds claimed in U.S. Patent 4,873,080? Yes, since the patent has expired, generic companies are free to manufacture and sell drugs that precisely fall within the scope of the expired claims in the United States, provided they do not infringe any other valid and enforceable patents.
What are the primary therapeutic areas mentioned in the patent? The patent mentions therapeutic applications in cardiovascular diseases, inflammatory and autoimmune diseases, bronchial asthma, and thromboembolic diseases.
What was the significance of the R2 and R3 substituents in the patent's claims? The R2 and R3 substituents were crucial for defining specific compounds within the broader class claimed by the patent. Variations in these substituents allowed for the protection of a range of related but distinct chemical entities.

Cited Sources

[1] Laboratoires Servier. (1989). U.S. Patent 4,873,080: 1-(2-Phenylacetyl)piperidine-3-carboxylic acid derivatives. United States Patent and Trademark Office.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
Germany	3320583	Jun 08, 1983

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	49886	⤷ Start Trial
Australia	2924184	⤷ Start Trial
Australia	562803	⤷ Start Trial
Canada	1228300	⤷ Start Trial
German Democratic Republic	223360	⤷ Start Trial
Germany	3320583	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,873,080

Summary for Patent: 4,873,080