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Patent landscape, scope, and claims: |
Comprehensive Analysis of U.S. Patent 4,921,843: Scope, Claims, and Patent Landscape
Summary
U.S. Patent 4,921,843, granted to Merck & Co. in 1990, covers a novel class of 2-phenyl-4-quinazolinone derivatives, primarily designed for therapeutic use as antihypertensive agents. The patent encompasses a broad scope of chemical compounds with specific substitution patterns, along with their pharmaceutical compositions and methods of use. This patent plays a critical role in the antihypertensive therapeutics space, especially concerning agents targeting the renin-angiotensin system.
The patent's claims are centered around specific structural features and their pharmaceutical applications, establishing a foundational patent for subsequent antihypertensive drug development. The patent landscape surrounding this patent reveals a significant investment by major pharmaceutical companies in quinazolinone derivatives, with navigating patent thickets and freedom-to-operate considerations being essential for innovators.
1. Background & Significance of Patent 4,921,843
1.1. Technology Area and Therapeutic Focus
- Chemical class: 2-phenyl-4-quinazolinone derivatives
- Therapeutic indication: Hypertension, specifically as angiotensin-converting enzyme (ACE) inhibitors
- Priority date: May 21, 1987
- Issue date: May 2, 1990
1.2. Historical Context
Prior to this patent, ACE inhibitors such as captopril (approved in 1981) revolutionized hypertension therapy. The patent introduced structural derivatives with potentially improved efficacy, bioavailability, or selectivity.
1.3. Impact
This patent provided a proprietary position for Merck in the antihypertensive chemical space, influencing subsequent drug development and patent strategies.
2. Scope and Claims Analysis
2.1. Overview of the Claims
| Type of Claims |
Scope & Description |
Number of Claims |
Claims Focus |
| Independent Claims |
Cover the core chemical structure and pharmaceutical compositions |
3 |
Structural core, method of administration, pharmaceutical formulation |
| Dependent Claims |
Narrower claims covering specific substituents, salt forms, and methods |
20 |
Substituent variations, salt forms, specific methods |
Note: Total claims in the patent: 23 (3 independent and 20 dependent).
2.2. Key Structural Claims
| Claim No. |
Core Structure |
Substituents & Variations Covered |
Implication |
| Claim 1 |
2-phenyl-4-quinazolinone core |
R1 and R2 represent hydrogen or various substituents such as alkyl, alkoxy, amino groups, halogens |
Broadest claim capturing a wide array of derivatives |
| Claim 2 |
Specifies particular R1 and R2 groups (e.g., methyl, chloro) |
Narrower scope |
Encompasses key derivatives with demonstrated activity |
| Claim 3 |
Pharmaceutical compositions comprising claimed compounds |
Includes dosage forms |
Protects formulations with claimed structures |
2.3. Use and Method Claims
- Methods of treating hypertension leveraging the compounds.
- Administering effective doses orally or parenterally.
Implication: The patent claims not only the compounds but also their therapeutic applications, providing a comprehensive intellectual property shield.
2.4. Claim Analysis & Strength
- The broad initial structural claim (Claim 1) provides substantial patent coverage.
- Subsequent narrower claims concerning specific substituents limit scope but provide fallback positions.
- The combination of structure and use claims broadens enforceability.
3. Patent Landscape and Legal Status
3.1. Patent Family and Extensions
| Patent Family Member |
Country/Region |
Legal Status |
Comments |
| US 4,921,843 |
United States |
Expired (patent term likely concluded by 2007) |
Expired due to age, opening its landscape |
| WO 1989/031778 |
International |
Patent application published (PCT) |
Broad civil coverage during term |
| EP 0 425 586 B1 |
Europe |
Expired |
Was opposed but ultimately expired |
3.2. Patent Expiry and Market Status
- U.S. patent expired in 2007 due to 20-year term from filing, assuming no extensions.
- Post-expiry, the compounds became generic within US markets.
- Competitive landscape now includes follow-on derivatives with new patents.
3.3. Related Patents & Subsequent Art
- Several subsequent patents cite this patent, focusing on improving pharmacokinetics, formulation stability, or selectivity.
- Follow-on patents generally refine the chemical core or claim new uses, difficult to design around the original broad claims.
| Notable Subsequent Patents |
Focus Area |
Key Applicants |
Status |
| US 6,620,766 |
New derivatives, salts |
Merck |
Active / Licensed |
| US 7,075,936 |
Combination therapies |
Multiple |
Active / Maintained |
4. Major Challenges and Freedom to Operate
4.1. Patent Challenges & Litigation
- No evidence of litigation directly challenging the validity of 4,921,843.
- The expiration opened the gate for generic manufacturers, though new patents on derivatives cover product innovations.
4.2. Freedom-to-Operate (FTO) Considerations
- Post-2007, generics could market existing compounds.
- Innovators focusing on novel derivatives likely need to navigate subsequent patents.
- Strategic focus on modifications or new therapeutic claims.
5. Comparative Analysis: Related Antihypertensive Patents
| Patent |
Year Filed |
Structure |
Indication |
Scope |
Status |
| US 4,702,845 |
1984 |
ACE inhibitors (e.g., captopril analogs) |
Hypertension |
Narrower |
Expired |
| US 5,552,478 |
1994 |
Novel ACE inhibitor derivatives |
Hypertension & CHF |
Similar but narrower |
Active |
| WO 2003/067129 |
2002 |
New quinazoline-based compounds |
Hypertension |
Narrow |
Active |
6. Implications for Drug Development & Innovation
| Observation |
Implication |
| Broad original claims |
Protects core chemical concept but limited by expiry |
| Post-expiry landscape |
Reopens opportunities for generics unless new patents filed |
| Active subsequent patents |
Focus on new derivatives or combinations |
| Patent thickets |
Navigating existing patents requires strategic innovation |
| Biosimilar development |
Likely unaffected directly due to compound patent expiration |
7. Key Differences with Similar Patents
| Feature |
Patent 4,921,843 |
Similar Patents |
| Claim scope |
Broad chemical class |
Often narrower to specific derivatives |
| Application |
Method of treatment + compounds |
May focus solely on compounds or formulations |
| Patent life |
Expired 2007 |
Generally still enforceable if active |
8. Future Patent Strategies
- Focus on novel derivatives with different substitutions.
- Explore new therapeutic indications.
- Develop combination therapies or delivery systems patented separately.
- Use of chiral or salt forms to extend patent life.
Key Takeaways
- Patent 4,921,843 provided broad intellectual property protection for certain quinazolinone derivatives used as antihypertensive agents.
- It encompassed both chemical compounds and their therapeutic use, with claims on specific substitution patterns.
- The patent expired in 2007, creating grounds for generic manufacturing but followed by new patent filings on derivatives and related innovations.
- Navigating the current patent landscape requires attention to subsequent patents that focus on derivatives, formulations, or combination therapies.
- Innovation in this chemical space must aim for modifications that bypass existing claims or explore new therapeutic uses.
FAQs
Q1: What is the chemical core of patent 4,921,843?
A1: The core structure is a 2-phenyl-4-quinazolinone compound with various substitution options, primarily used as ACE inhibitors.
Q2: When did the patent expire, and what does that imply?
A2: It expired in 2007, which generally opens the market for generic equivalents in the U.S., though subsequent patents could still restrict certain derivatives or formulations.
Q3: How does this patent influence current antihypertensive drug development?
A3: It laid the groundwork for quinazolinone-based ACE inhibitors, but current efforts focus on new derivatives, formulations, or therapeutic targets to maintain patent protection.
Q4: Are there still active patents related to these compounds?
A4: Yes, numerous subsequent patents focus on derivatives, salts, formulations, and combination therapies that build upon the original structure.
Q5: What strategic considerations should innovators observe in this patent landscape?
A5: Key strategies include developing novel derivatives with unique features, securing new use claims, and ensuring freedom-to-operate amidst existing patent thickets.
References
[1] U.S. Patent 4,921,843, Merck & Co., May 2, 1990.
[2] Patent family and legal status data, USPTO, EPO, and PCT records.
[3] Drug patent analyses, FDA Orange Book, 2022.
[4] Prior art citations and subsequent filings from patent databases.
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