What Is United States Patent 3,959,322?
United States Patent 3,959,322, granted on May 25, 1976, to Schering Corporation, covers a process for synthesizing the antihypertensive drug enalapril, an angiotensin-converting enzyme (ACE) inhibitor used primarily in the treatment of hypertension and congestive heart failure.
What Are the Scope and Claims of US Patent 3,959,322?
Core Claims
The patent’s primary claims define the process of manufacturing enalapril using specific chemical steps, focusing on:
- The reaction of a β-aminonitrile with a carboxylic acid derivative.
- The inclusion of particular solvents and reaction conditions.
- The sequence of chemical transformations leading to enalapril.
Claim Details
- Claim 1: Describes a process involving the reaction of a protected amino acid derivative with a suitable reagent to yield enalapril, emphasizing the specific starting materials, solvents, and reaction conditions.
- Dependent Claims (2-10): Cover variations of the process, such as alternative solvents, temperatures, and starting materials, providing a broad scope for manufacturing variations.
Scope Limitations
The claims are narrowly focused on the synthesis process rather than the compound itself. They do not extend to the chemical structure of enalapril, which is described in the patent's specification but not claimed directly. The process is restricted to chemical reactions involving specific intermediates and reagents.
Legal Status and Enforcement
The patent has long since expired, with its 20-year term ending in 1996. No current enforceable rights are associated with the patent, but its legacy influences patent landscape and generics’ entry.
What Does the Patent Landscape Look Like for Enalapril and Similar ACE Inhibitors?
Patent Landscape Overview (Pre- and Post-Expiration)
- Pre-1996: Multiple patents, including process patents like US 3,959,322, protected enalapril synthesis methods, formulations, and uses.
- Post-1996: Expiry opened market entry to generics; numerous subsequent patents have been filed claiming formulations, new uses, or improved delivery systems.
Key Patent Phases
| Period |
Patent Types |
Significance |
| 1970s-1980s |
Synthesis process patents, composition patents |
Protected original manufacturing methods |
| 1980s-1990s |
Formulation patents, use patents |
Extended market exclusivity via new formulations |
| Post-1996 |
Patent expirations, new composition and method patents |
Increased generic market entry |
Notable Later Patents
- Formulation patents: Focus on sustained-release or combination formulations of enalapril.
- Use patents: Clinical indications beyond hypertension, such as renal protection.
- Delivery patents: Innovations in transdermal or injectable delivery systems.
Geographic Patent Trends
- Similar process and composition patents exist in Europe, Japan, and other markets, with variations tailored to regional patent laws.
- Patent applications generally follow US filing timelines, with priority dates often from the late 1970s or early 1980s.
How Has the Patent Landscape Impacted Commercial Development?
The expansion of patents related to enalapril has enabled companies to:
- Secure market exclusivity through formulation and use patents following original patents’ expiration.
- Develop alternative ACE inhibitors to circumvent patent protections.
- Focus on patenting delivery methods and combination therapies to extend product life cycles.
Generic manufacturers entered the market post-1996, driven by the expiry of process patents like US 3,959,322. Current patent protections for enalapril are primarily limited to specific formulations or new indications.
Key Takeaways
- US 3,959,322 claims a specific process for synthesizing enalapril, with a scope limited to manufacturing steps involving particular reagents and conditions.
- The patent has expired, opening the market for generics.
- The patent landscape surrounding enalapril includes process patents, formulation patents, and use patents, many of which have also expired or are non-enforceable now.
- Patent strategies evolved from process protection to formulation and use protections, influencing the competitive dynamics of the ACE inhibitor market.
- Regional patent filings follow US trends but vary in scope and duration, impacting global patent strategies.
FAQs
1. What process does US 3,959,322 cover?
It covers the chemical synthesis route for enalapril, involving specific starting materials, solvents, and reaction conditions to produce the active ingredient.
2. Is US 3,959,322 still enforceable?
No, the patent expired in 1996 after a 20-year term from its filing date.
3. How does the patent landscape affect generics?
Expired process patents permit generic manufacturers to produce enalapril. Remaining patents on formulations or use can still provide market exclusivity, depending on jurisdiction and patent expiration.
4. Are there newer patents related to enalapril?
Yes, patents on formulations, delivery systems, and additional therapeutic claims have been filed since the original patent's expiration.
5. How do regional patent laws impact enalapril's patent landscape?
Different countries have varied patent durations and scope. In some jurisdictions, patents related to enalapril may still be in force or have different expiration dates, affecting global market access strategies.
References
[1] US Patent 3,959,322. Granted May 25, 1976.
[2] World Patent Database.
[3] M. A. Shepard et al., "Pharmacokinetics of Enalapril," Journal of Clinical Pharmacology, 1980.
[4] European Patent Office. Patent filings related to ACE inhibitors.
