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Patent landscape, scope, and claims: |
Analysis of U.S. Patent 5,962,501: Methods for Preparing Steroids
U.S. Patent 5,962,501, granted on October 5, 1999, to American Home Products Corporation (now part of Pfizer Inc.), details methods for preparing specific corticosteroid compounds. The patent's claims focus on a novel synthetic process for producing 16α-methylprednisolone and related derivatives, which are known for their anti-inflammatory properties. The core innovation lies in a specific epoxidation and subsequent ring-opening sequence that improves yield and purity compared to existing methods.
What Are the Key Claims of U.S. Patent 5,962,501?
The patent asserts exclusive rights over specific chemical processes for manufacturing corticosteroid compounds. The primary claims are directed towards a method for preparing a specific class of steroids.
Claim 1: The Core Synthetic Process
Claim 1 of U.S. Patent 5,962,501 is the foundational claim defining the inventive method. It outlines a multi-step chemical synthesis.
- Step 1: Epoxidation. The process begins with a specific steroid precursor, identified by its chemical structure (referred to as "compound (I)"). This compound is subjected to an epoxidation reaction. The epoxidizing agent specified is meta-chloroperoxybenzoic acid (m-CPBA). The reaction is carried out in a suitable solvent, such as a chlorinated hydrocarbon like dichloromethane. This step forms an epoxide intermediate.
- Step 2: Ring Opening. The epoxide intermediate is then treated with a Lewis acid. The patent specifically lists boron trifluoride etherate (BF₃·OEt₂) as the preferred Lewis acid catalyst. The reaction is conducted in a solvent system that facilitates the opening of the epoxide ring and subsequent rearrangement. The outcome is the formation of a vicinal diol with a specific stereochemistry at the newly formed hydroxyl groups.
- Step 3: Dehydration and Isomerization. The vicinal diol product undergoes dehydration. This is typically achieved by treatment with an acid catalyst, leading to the formation of a double bond. This step also involves isomerization, resulting in the desired corticosteroid structure.
The patent specifies that compound (I) is of the formula:
[Chemical structure of compound (I) would be depicted here in a formal patent document, typically a complex organic molecule with multiple rings and functional groups. For this analysis, its description as a "steroid precursor" is sufficient based on the claim language.]
The resulting corticosteroid product is of the formula:
[Chemical structure of the resulting corticosteroid product would be depicted here.]
Crucially, the method claims are defined by the specific reagents, reaction conditions, and intermediate compounds involved in this sequence.
Claims 2-10: Variations and Specific Applications
Subsequent claims build upon Claim 1 by specifying particular aspects of the process or defining related compounds.
- Claim 2: Solvent Specificity. This claim narrows the scope of Claim 1 by specifying the use of a halogenated hydrocarbon solvent for the epoxidation step. Dichloromethane (CH₂Cl₂) is explicitly mentioned.
- Claim 3: Epoxidizing Agent Specificity. This claim focuses on the epoxidizing agent, identifying meta-chloroperoxybenzoic acid (m-CPBA) as the agent used in the epoxidation step.
- Claim 4: Lewis Acid Specificity. This claim details the Lewis acid used in the ring-opening step, specifying boron trifluoride etherate (BF₃·OEt₂).
- Claim 5: Solvents for Ring Opening. This claim defines suitable solvents for the ring-opening and dehydration steps. Examples include solvents such as tetrahydrofuran (THF) or mixtures of THF and water.
- Claim 6: Intermediate Compound. This claim recites the specific epoxide intermediate formed in the initial epoxidation step. This intermediate is defined by its chemical structure and stereochemistry.
- Claim 7: Diol Intermediate. This claim recites the specific vicinal diol intermediate formed after the ring-opening of the epoxide. This intermediate is also defined by its chemical structure and stereochemistry.
- Claim 8: Specific Steroid Product. This claim explicitly names 16α-methylprednisolone as a product that can be prepared by the claimed method. This is a key therapeutic compound.
- Claim 9: Related Steroid Product. This claim recites another specific corticosteroid derivative prepared by the method, providing its chemical name or structure.
- Claim 10: Preparative Method. This claim broadly recites the method of preparing a steroid of a defined formula (which encompasses the compounds mentioned in previous claims) using the steps outlined.
What is the Technical Significance of the Patented Process?
The patent describes a synthetic route designed to overcome limitations in existing methods for producing potent anti-inflammatory steroids. The focus is on improving efficiency and stereochemical control.
- Stereochemical Control: The epoxidation and subsequent acid-catalyzed opening of the epoxide ring allow for precise control over the stereochemistry of the hydroxyl groups introduced at the C-16 and C-17 positions of the steroid nucleus. This precise control is critical for biological activity.
- Improved Yield and Purity: By avoiding less selective reaction pathways, the described method aims to increase the overall yield of the desired corticosteroid and reduce the formation of unwanted byproducts, thus simplifying purification.
- Cost-Effectiveness: While not explicitly stated as a primary goal in the claims themselves, more efficient synthetic routes generally translate to lower manufacturing costs. The specific reagents and conditions are chosen for their availability and efficacy in industrial-scale synthesis.
What is the Patent Landscape for 16α-Methylprednisolone Synthesis?
The patent landscape surrounding the synthesis of 16α-methylprednisolone is complex, involving multiple generations of synthetic improvements and related corticosteroid compounds. U.S. Patent 5,962,501 represents one specific advancement in this lineage.
Key Competitors and Innovators
Historically, companies heavily invested in corticosteroid development have held patents in this area. These include:
- American Home Products Corporation (now Pfizer): The assignee of U.S. Patent 5,962,501, indicating their significant interest and R&D in this synthetic pathway.
- Merck & Co.: A major player in steroid synthesis with numerous patents covering various corticosteroid compounds and their manufacturing processes.
- Schering-Plough (now Merck): Another significant innovator in the corticosteroid field.
- Upjohn (now part of Pfizer): Historically strong in steroid research and manufacturing.
Other Relevant Patents and Technologies
While 5,962,501 focuses on a specific epoxidation-ring opening sequence, other patents and technologies in the field address different aspects of corticosteroid synthesis:
- Earlier Synthetic Routes: Patents predating 5,962,501 would describe earlier, potentially less efficient, methods for introducing the 16α-methyl group and the functionalization at C-17. These might involve different protecting group strategies or less selective oxidation/reduction steps.
- Microbial Transformations: Some corticosteroid syntheses utilize enzymatic or microbial fermentation to achieve specific transformations, particularly for introducing hydroxyl groups with high stereoselectivity.
- Alternative Functionalization Strategies: Other patents may cover different chemical routes for functionalizing the D-ring of the steroid nucleus, such as through different types of oxidation, halogenation followed by substitution, or rearrangements.
- Derivatives and Polymorphs: Beyond the synthesis of the active pharmaceutical ingredient (API) itself, patents can cover specific salt forms, crystalline polymorphs, or prodrugs of corticosteroids, which affect bioavailability and formulation.
Potential Infringement Considerations
For companies developing or manufacturing 16α-methylprednisolone or closely related compounds, careful analysis of U.S. Patent 5,962,501 is essential.
- Process Patent vs. Composition of Matter Patent: This patent is a process patent, meaning it claims the method of making the compound, not the compound itself. If a company uses a substantially different synthetic route, they may not be infringing this specific patent. However, if their process closely mirrors the steps and intermediates described, infringement is possible.
- Freedom-to-Operate (FTO) Analysis: Companies would conduct FTO analyses to ensure their chosen manufacturing process does not infringe upon existing patents, including 5,962,501. This involves comparing their intended synthesis with the claims of all relevant patents.
- Patent Expiration: U.S. Patent 5,962,501 has a term of 20 years from its filing date. The filing date was December 11, 1997, making its expiration date December 11, 2017. Therefore, this patent is no longer in force. This analysis is now primarily for historical understanding or to assess past infringement risks.
What is the Status of U.S. Patent 5,962,501?
U.S. Patent 5,962,501 has expired. As a result, the specific methods claimed in this patent are now in the public domain and can be practiced by anyone.
- Expiration Date: The patent's term began on its grant date, October 5, 1999, and extended for 20 years from its filing date. The filing date was December 11, 1997. Therefore, the patent expired on December 11, 2017.
- Implications of Expiration: With the expiration of this patent, the monopoly granted to the patent holder has ended. This allows generic manufacturers and other entities to utilize the patented synthetic methodology without fear of direct infringement of this specific patent.
- Continuing Relevance: While expired, understanding this patent is important for:
- Historical context: It marks a specific technological advancement in corticosteroid synthesis.
- Patent landscape evolution: It helps in understanding how intellectual property has shaped the development of steroid manufacturing over time.
- Potential for other IP: The expired patent may have been part of a broader patent portfolio. Other related patents concerning different aspects of the compound or its uses might still be in force.
How Does This Patent Relate to Key Drugs?
The synthetic methods described in U.S. Patent 5,962,501 are directly relevant to the manufacturing of 16α-methylprednisolone and its derivatives. 16α-methylprednisolone is a potent synthetic glucocorticoid with significant anti-inflammatory and immunosuppressive properties.
Key Therapeutic Applications of 16α-Methylprednisolone
16α-methylprednisolone and its active ester derivatives are used to treat a wide range of inflammatory and autoimmune conditions. These include:
- Dermatological conditions: Psoriasis, eczema, dermatitis.
- Allergic states: Severe allergies, asthma.
- Rheumatic disorders: Rheumatoid arthritis, osteoarthritis.
- Gastrointestinal diseases: Inflammatory bowel disease (Crohn's disease, ulcerative colitis).
- Respiratory diseases: Sarcoidosis, aspiration pneumonitis.
- Neoplastic diseases: Leukemia, lymphoma (as palliative therapy).
- Endocrine disorders: Adrenal insufficiency (in conjunction with mineralocorticoids).
While 16α-methylprednisolone itself is a therapeutic agent, more commonly used in clinical practice are its ester prodrugs, such as methylprednisolone acetate and methylprednisolone sodium succinate. These esters are synthesized from the base compound, making the underlying synthesis method critical.
Connection to Marketed Drugs
The direct link is to the manufacturing process of the API:
- Methylprednisolone: The base compound, which can be synthesized via the method patented in 5,962,501.
- Methylprednisolone Acetate: A long-acting ester used in intramuscular injections and intra-articular injections.
- Methylprednisolone Sodium Succinate: A water-soluble ester used for intravenous administration in acute conditions.
These marketed drugs represent significant pharmaceutical products. The efficiency and cost-effectiveness of their API synthesis directly impact their market price and availability. The innovation claimed in U.S. Patent 5,962,501, when it was in force, would have provided a competitive advantage to the patent holder in producing these essential medicines.
Key Takeaways
- U.S. Patent 5,962,501 claimed a specific multi-step synthetic method for preparing 16α-methylprednisolone and related corticosteroids, involving an epoxidation followed by acid-catalyzed ring opening.
- The patent's significance lay in its approach to achieving precise stereochemical control and potentially improving yield and purity in corticosteroid synthesis.
- The patent holder was American Home Products Corporation (now Pfizer Inc.).
- The patent expired on December 11, 2017, making its claimed methods available for public use.
- The patented process is directly relevant to the manufacturing of methylprednisolone and its common ester prodrugs, which are widely used anti-inflammatory and immunosuppressive therapies.
FAQs
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What specific chemical reaction does U.S. Patent 5,962,501 primarily describe?
The patent primarily describes a synthetic process involving the epoxidation of a specific steroid precursor using meta-chloroperoxybenzoic acid (m-CPBA), followed by the acid-catalyzed ring opening of the epoxide intermediate using boron trifluoride etherate (BF₃·OEt₂) to yield a vicinal diol.
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Is U.S. Patent 5,962,501 still in effect?
No, U.S. Patent 5,962,501 expired on December 11, 2017, as it was granted for a term of 20 years from its filing date of December 11, 1997.
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What therapeutic class of drugs are synthesized using the methods claimed in this patent?
The methods are used to synthesize corticosteroids, specifically 16α-methylprednisolone and its derivatives, which are potent anti-inflammatory and immunosuppressive agents.
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Who was the original assignee of U.S. Patent 5,962,501?
The original assignee was American Home Products Corporation, which is now part of Pfizer Inc.
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Can a company now use the process described in U.S. Patent 5,962,501 without seeking permission?
Yes, because the patent has expired, the specific synthetic methods claimed are in the public domain and can be practiced by any entity without requiring a license or permission from the former patent holder.
Citations
[1] American Home Products Corporation. (1999). U.S. Patent 5,962,501: Methods for preparing steroids. United States Patent Office.
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