United States Patent 4,001,301: Claim Scope, Naproxen Coverage, Expiration, and Patent Landscape

U.S. Patent No. 4,001,301 covered substituted 2-naphthyl alpha-methylacetic acids, their C1-C12 alkyl esters, and pharmaceutically acceptable addition salts. The claims divided into two chemical series: 6-alkoxy compounds, including the methoxy compound associated with naproxen, and 6-alkylthio compounds, including the methylthio analog in claim 10.

The patent issued on January 4, 1977. Under the pre-Uruguay Round patent term applicable to the patent, the ordinary term was 17 years from issuance. The patent therefore expired in January 1994, absent an unusual term adjustment or restoration. It does not create current U.S. generic-entry or biosimilar barriers. [1][2]

What compounds does U.S. Patent 4,001,301 protect?

The patent covers a substituted naphthalene ring bearing an alpha-methylacetic acid side chain, together with specified oxygen- and sulfur-containing substituents at the 6-position.

The claims can be separated as follows:

Claim group	Core substituent	Alpha substituent	Covered forms
Claims 1-4	6-alkoxy, C1-C6	Methyl or ethyl	Free acids, C1-C12 alkyl esters, pharmaceutically acceptable salts
Claims 5-8	6-alkylthio, C1-C6	Methyl or ethyl	Free acids, C1-C12 alkyl esters, pharmaceutically acceptable salts
Claim 9	6-methoxy	Alpha-methyl	Methyl ester
Claim 10	6-methylthio	Alpha-methyl	Free acid

The supplied text does not reproduce the structural drawings identified as Formula XIV and Formula XV. The written limitations nevertheless establish the principal chemical boundaries. The exact positional and stereochemical scope depends on the structures shown in the issued patent.

What is the significance of the R7 limitation?

R7 defines the substituent attached to the naphthalene ring:

In claims 1-4, R7 is alkoxy containing one to six carbon atoms.
In claims 5-8, R7 is alkylthio containing one to six carbon atoms.

The alkoxy class includes methoxy, ethoxy, propoxy and other C1-C6 alkoxy groups. Claim 3 narrows the first series to methoxy. Claim 6 narrows the sulfur series to methylthio.

The broad genus claims therefore cover more compounds than naproxen itself. Naproxen corresponds to the 6-methoxy, alpha-methyl member of the oxygen series, subject to the stereochemical configuration represented or required by Formula XIV.

Does Patent 4,001,301 cover naproxen?

Yes, claim 4 is directed to the 6-methoxy, alpha-methyl compound in the Formula XIV series. That structure is the naproxen acid structure when the claimed naphthalene side chain and stereochemistry correspond to naproxen.

Naproxen is commonly identified chemically as (S)-6-methoxy-alpha-methyl-2-naphthaleneacetic acid. The patent’s claim language is broader than the single commercial enantiomer if the formula does not restrict the stereocenter to the S configuration. A claim to the compound without an express stereochemical limitation generally raises a scope question as to whether it covers both enantiomers, a racemate, or only the depicted configuration. That issue must be resolved against the patent’s drawings, specification and prosecution history.

The patent also covers related forms:

Alkyl esters derived from alkanols containing one to 12 carbon atoms.
Pharmaceutically acceptable addition salts.
The specifically recited methyl ester in claim 9.
The free acid, rather than only an ester, within the claim 4 combination.

What does claim 9 protect?

Claim 9 specifically claims methyl 6-methoxy-2-naphthyl-alpha-methylacetate. This is the methyl ester of the 6-methoxy alpha-methyl compound.

Claim 9 is narrower than the genus in claim 1 because it specifies:

The methoxy substituent.
The alpha-methyl group.
The methyl ester.

It is also structurally distinct from the free-acid form of naproxen. A commercial product containing naproxen acid would not be analyzed solely under claim 9 because claim 9 recites the methyl ester.

What does claim 10 protect?

Claim 10 claims 6-methylthio-2-naphthyl-alpha-methylacetic acid. This compound is in the sulfur-containing series and is separate from the methoxy naproxen series.

Claim 10 is an independent compound claim as presented. It does not depend on claim 5 and does not require an ester or salt. It covers the specified free acid, subject to the structure and stereochemistry shown in the patent.

How broad are claims 1 through 8?

Claims 1 and 5 are the principal genus claims.

Claim 1 requires:

A Formula XIV compound.
R7 as C1-C6 alkoxy.
One of R10 and R11 as hydrogen.
The other as methyl or ethyl.
The corresponding C1-C12 alkyl esters.
Pharmaceutically acceptable addition salts.

Claim 5 uses the same alpha-substitution pattern but replaces alkoxy with C1-C6 alkylthio.

The dependent claims narrow the genus:

Claim	Narrowing limitation
Claim 2	Alpha substituent is methyl rather than methyl or ethyl
Claim 3	R7 is methoxy
Claim 4	R7 is methoxy and alpha substituent is methyl
Claim 6	R7 is methylthio
Claim 7	Alpha substituent is methyl
Claim 8	R7 is methylthio and alpha substituent is methyl

The claim architecture is cumulative. Claim 4 is the most relevant claim for naproxen-type compounds in the oxygen series. Claim 8 is the corresponding narrow claim for the methylthio series.

What formulations and pharmaceutical forms are protected?

The claims protect chemical forms, not a finished dosage-form formulation.

Alkyl esters

The claims include esters derived from alkanols containing one to 12 carbon atoms. This language potentially covers methyl, ethyl, propyl, butyl and higher alkyl esters through the C12 boundary.

The ester limitation is important because esterification changes the claimed molecule. A product containing the free acid is not automatically identical to a product containing a methyl or other alkyl ester.

Pharmaceutically acceptable salts

The claims also include pharmaceutically acceptable addition salts. For an acidic naphthaleneacetic acid, this generally points to salts formed with pharmaceutically acceptable bases, although the patent specification controls the precise salt disclosure and construction.

A salt claim can cover a marketed pharmaceutical salt even when the neutral acid is not the form administered. Salt coverage does not, by itself, create a formulation claim to tablets, capsules, suspensions, coatings or release profiles.

Dosage forms

The supplied claims do not recite:

Immediate-release tablets.
Sustained-release tablets.
Enteric coatings.
Injectable compositions.
Specific excipients.
Particle-size distributions.
Dissolution parameters.
Manufacturing processes.
Combination products.

A formulation patent or process patent would therefore need to be analyzed separately from Patent 4,001,301.

When did U.S. Patent 4,001,301 expire?

The patent issued on January 4, 1977. The applicable pre-1995 term was generally 17 years from grant. On that basis, the ordinary expiration date was January 4, 1994. [1][2]

Event	Date or status
U.S. patent issued	January 4, 1977
Applicable ordinary term	17 years from issue
Ordinary expiration	January 4, 1994
Current status	Expired
Current blocking effect	None from this patent

The patent predates the modern 20-year-from-earliest-effective-filing-date regime. The Uruguay Round Agreements Act changed the term for later-filed applications, but it did not convert this patent into a live 20-year patent running from its earliest priority date.

What is the Orange Book status of Patent 4,001,301?

Patent 4,001,301 should not be treated as a current Orange Book barrier.

The FDA Orange Book lists patents submitted by an approved new drug application holder for a specific drug product. Listing status is product-specific and does not establish that every claim in a patent covers the active ingredient or every marketed formulation. The Orange Book also does not revive an expired patent. [3]

For naproxen products, historical Orange Book analysis should distinguish:

The naproxen active ingredient.
Naproxen sodium products.
Prescription and over-the-counter products.
Product-specific formulation patents.
Method-of-use patents.
Expired compound patents.

Patent 4,001,301 is a historical compound patent. Its expiration removes it as a current obstacle to an abbreviated new drug application. A current applicant would still need to address any separately listed, unexpired patents associated with the target reference product.

Were there Paragraph IV challenges to this patent?

A current Paragraph IV certification against Patent 4,001,301 would not be commercially relevant because the patent expired in 1994.

Paragraph IV litigation generally arises when an ANDA applicant certifies that a listed patent is invalid, unenforceable or not infringed. An expired patent does not support a conventional stay of ANDA approval or a continuing patent-based launch injunction. [4]

Historical generic competition involving naproxen was more likely to involve:

Other compound patents.
Naproxen sodium patents.
Formulation patents.
Product-specific Orange Book listings.
Regulatory exclusivity rather than this patent alone.

No conclusion that Patent 4,001,301 itself generated a meaningful current Paragraph IV risk is supportable after expiration.

What patent landscape surrounded naproxen?

The naproxen estate historically included more than one patent family. The relevant categories were:

Estate category	Typical subject matter	Present relevance
Compound patents	Substituted naphthaleneacetic acids	Expired
Stereochemical patents	Single-enantiomer naproxen	Requires family-specific review
Salt patents	Naproxen sodium and related salts	Requires patent-by-patent review
Ester or prodrug patents	Modified naproxen derivatives	Usually expired for early families
Formulation patents	Tablets, suspensions, release profiles	Product-specific
Method-of-use patents	Pain, inflammation and related indications	Generally expired for early naproxen products
Manufacturing patents	Resolution, synthesis and purification	Potential historical process barriers
Regulatory exclusivity	New drug or pediatric exclusivity	Time-limited and product-specific

U.S. Patent 3,904,682 is commonly associated with the earlier naproxen patent estate and should be reviewed alongside Patent 4,001,301 when reconstructing historical compound coverage. The two patents should not be assumed to have identical claim scope. Patent 4,001,301 expressly includes the alkoxy and alkylthio classes reflected in the supplied claims, while an earlier family member may contain different genus, process or stereochemical claims.

How strong was the patent estate?

The patent estate was technically strong during its operative term for compounds falling squarely within the claimed structures. The strongest features were:

Broad genus coverage for C1-C6 alkoxy and alkylthio substituents.
Coverage of both free acids and C1-C12 alkyl esters.
Inclusion of pharmaceutically acceptable salts.
Narrow fallback claims for the methoxy and methylthio embodiments.
A specific methyl ester claim and a specific methylthio acid claim.

Its limitations were equally important:

The claim text depends on Formula XIV and related structural drawings.
Stereochemical scope may require prosecution-history analysis.
The claims do not cover every formulation or manufacturing process.
The patent expired decades ago.
Any current commercial threat would have to arise from a different patent family or regulatory right.

The patent therefore had meaningful historical blocking value but has no current exclusionary value in the U.S.

Which companies challenged or competed against the naproxen estate?

The original research and commercial development of naproxen are associated with Syntex. Roche later acquired Syntex, while naproxen products were commercialized through prescription and over-the-counter channels involving multiple product sponsors and licensees.

Generic competition emerged after the relevant compound and regulatory protections expired. FDA approval records and the Orange Book should be used to identify specific ANDA sponsors, reference listed drugs and product-level patent certifications. [3][5]

The patent record alone does not establish the terms of any license, settlement or commercialization agreement. Patent 4,001,301 contains no licensing terms. Any deal analysis must rely on separate assignment records, SEC filings, court dockets or transaction documents.

What generic launch risks existed?

For a product corresponding to naproxen or a covered analog, the risk profile was:

During the patent term

A product practicing the compound claims could face infringement exposure. Design-around options would have included:

Selecting a substituent outside the C1-C6 alkoxy and alkylthio ranges.
Altering the alpha substituent.
Using a chemically distinct active ingredient.
Avoiding a claimed ester or salt.
Challenging validity, enforceability or claim construction.

Those strategies would require technical confirmation because a change outside one limitation does not eliminate potential infringement under other patent families.

After expiration

After January 1994, Patent 4,001,301 no longer blocked launch. A generic applicant would still need to evaluate other patents listed for the selected reference product, but this patent would not support a current injunction or regulatory delay.

Does biosimilar risk apply?

No. Naproxen is a chemically synthesized small-molecule drug, not a biologic. The relevant competitive pathway is an ANDA under section 505(j) of the Federal Food, Drug, and Cosmetic Act, not a biosimilar application under the Public Health Service Act.

Patent 4,001,301 therefore presents generic, not biosimilar, analysis. Its expiration eliminates any current patent-based exclusivity associated with the claimed compounds.

Key Takeaways

U.S. Patent 4,001,301 covered 6-alkoxy and 6-alkylthio substituted naphthyl alpha-methylacetic acids.
Claims 1-4 cover the oxygen series; claims 5-8 cover the sulfur series.
Claim 4 is the key naproxen-type claim because it specifies methoxy substitution and an alpha-methyl group.
Claim 9 covers the methyl ester of the 6-methoxy compound.
Claim 10 covers 6-methylthio-2-naphthyl-alpha-methylacetic acid.
The patent issued January 4, 1977 and ordinarily expired January 4, 1994.
It is not a current Orange Book or Paragraph IV barrier.
The claims do not expressly cover specific tablets, coatings, release profiles or manufacturing processes.
Current naproxen launch analysis requires separate review of product-specific compound, salt, formulation and method-of-use patents.
Biosimilar analysis does not apply because naproxen is a small molecule.

Frequently Asked Questions

Is naproxen still protected by U.S. Patent 4,001,301?

No. The patent’s ordinary term expired in January 1994.

Does claim 9 cover naproxen sodium?

No. Claim 9 specifically recites the methyl ester. Naproxen sodium is a salt form and must be analyzed under the applicable salt and product claims, not claim 9 alone.

Does Patent 4,001,301 cover the S-enantiomer of naproxen?

It may cover the S-enantiomer if the Formula XIV structure and intrinsic disclosure encompass that configuration. The final answer depends on the patent drawings and prosecution history.

Can a generic manufacturer launch naproxen based solely on expiration of this patent?

Patent 4,001,301 would not prevent launch, but the manufacturer must evaluate other patents listed for the relevant reference product and satisfy FDA ANDA requirements.

Does the patent cover naproxen formulations?

Not expressly. The supplied claims cover compounds, esters and salts. A formulation would require separate claim language directed to the dosage form, excipients, release characteristics or manufacturing process.

References

United States Patent and Trademark Office. (1977). U.S. Patent No. 4,001,301.
United States Code, 35 U.S.C. § 154. Patent term provisions.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book.
U.S. Food and Drug Administration. (2024). Abbreviated new drug application submissions: Patent certifications and 30-month stays.
U.S. Food and Drug Administration. (2024). Drugs@FDA: FDA-approved drugs database.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Australia	1006270	⤷ Start Trial
Belgium	734275	⤷ Start Trial
Belgium	747812	⤷ Start Trial
Belgium	751445	⤷ Start Trial
Belgium	752627	⤷ Start Trial
Brazil	6910380	⤷ Start Trial
Brazil	6915470	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,001,301

Summary for Patent: 4,001,301