US Patent 3,987,052: Scope, Claims, Expiration, and Triazolobenzodiazepine Patent Landscape

US Patent 3,987,052 is the foundational U.S. composition-of-matter patent for a broad class of 6-phenyl-4H-s-triazolo[4,3-a][1,4]benzodiazepines. Its most commercially important disclosed compound is alprazolam, identified in claim 2 as 8-chloro-1-methyl-6-phenyl-4H-s-triazolo[4,3-a][1,4]benzodiazepine. The patent also claims closely related compounds, including triazolam and multiple substituted analogs.

The patent was granted on October 19, 1976, and, under the pre-1995 U.S. patent-term regime, expired in 1993, subject to any applicable terminal-disclaimer or prosecution adjustments. It no longer creates a U.S. patent barrier to generic alprazolam, triazolam, or the other claimed compounds. Current commercial protection, where it exists, would have to arise from later patents covering formulations, dosage forms, delivery technologies, or specific methods of use rather than from US 3,987,052 itself. [1][4]

What compounds does US Patent 3,987,052 protect?

Claim 1 is a Markush composition-of-matter claim covering a large genus of triazolobenzodiazepines and their pharmacologically acceptable acid-addition salts.

The claimed core is:

A 4H-s-triazolo[4,3-a][1,4]benzodiazepine ring system.
A phenyl group at the 6-position.
Substituent R at the 1-position.
Substituent R1 in the fused triazole portion.
Substituents R2 through R5 on the phenyl and benzodiazepine ring system.
Acid-addition salts of the claimed compounds.

The principal structural limitations are summarized below.

Claim element	Permitted substituents
R	Hydrogen, C1-C3 alkyl, phenyl, or benzyl
R1	Hydrogen or C1-C3 alkyl
R2-R5	Hydrogen, C1-C3 alkyl, halogen, nitro, cyano, trifluoromethyl, alkoxy, alkylthio, alkylsulfinyl, alkylsulfonyl, alkanoylamino, or dialkylamino
Heteroatom substituent chains	C1-C3 carbon moieties
Salt form	Pharmacologically acceptable acid-addition salts

The claim is a classic genus claim. It does not protect every triazolobenzodiazepine. A compound must satisfy the claimed ring system, substitution pattern, and permitted substituent categories. Compounds outside the listed substituent classes, compounds with different ring fusion, or compounds lacking the claimed 6-phenyl triazolobenzodiazepine structure would fall outside the literal scope of claim 1.

Which marketed drugs are identified in the patent claims?

Several claims identify specific compounds. The most commercially significant are alprazolam and triazolam.

Patent claim	Compound	Commercial relevance
Claim 2	8-chloro-1-methyl-6-phenyl compound	Alprazolam
Claim 3	8-chloro-1-methyl-6-(2,6-difluorophenyl) compound	Specific difluorophenyl analog
Claim 4	8-chloro-1-methyl-6-(o-fluorophenyl) compound	Specific fluorophenyl analog
Claim 5	1-methyl-6-phenyl compound without 8-chloro	Unsubstituted analog
Claim 6	8-chloro-1-propyl-6-phenyl compound	N-propyl analog
Claim 7	8-chloro-1,6-diphenyl compound	N-phenyl analog
Claim 8	1-benzyl-8-chloro-6-phenyl compound	N-benzyl analog
Claim 9	1-ethyl-8-chloro-6-phenyl compound	N-ethyl analog
Claim 10	1-methyl-6-phenyl-8-trifluoromethyl compound	Trifluoromethyl analog
Claim 11	1-methyl-8-nitro-6-phenyl compound	Nitro analog
Claim 12	8-chloro-1-methyl-6-(o-chlorophenyl) compound	Triazolam
Claim 13	8-chloro-6-phenyl compound	Desmethyl analog
Claim 14	8-methylthio-1-methyl-6-phenyl compound	Methylthio analog
Claim 15	8-methoxy-1-methyl-6-phenyl compound	Methoxy analog

The text supplied for claims 8 and 15 contains apparent typographical or transcription errors. Claim 8 repeats part of the ring-system nomenclature, and claim 15 appears to omit "methyl" after "1-." The chemical identities can nevertheless be reconstructed from the substituent definitions and the claim language.

What patent claim covers alprazolam?

Claim 2 specifically covers alprazolam as a compound.

Alprazolam is:

A triazolobenzodiazepine.
Substituted with methyl at the 1-position.
Substituted with chlorine at the 8-position.
Substituted with phenyl at the 6-position.
Included within the broader genus of claim 1.
Expressly recited in dependent claim 2.

The claim is a product claim, not a method-of-treatment claim. It reaches the compound itself and, through claim 1, its pharmacologically acceptable acid-addition salts. Product claims generally provide broad control over manufacture, sale, and use of the claimed compound during the patent term, subject to applicable statutory defenses and regulatory exceptions.

Because the patent expired in 1993, claim 2 no longer blocks manufacture or sale of alprazolam in the United States. FDA approval of generic alprazolam products therefore proceeds through the abbreviated new drug application pathway rather than through licensing from the patent owner, assuming no later enforceable patent applies. [2][3]

Does US Patent 3,987,052 cover triazolam?

Yes. Claim 12 identifies triazolam as 8-chloro-1-methyl-6-(o-chlorophenyl)-4H-s-triazolo[4,3-a][1,4]benzodiazepine.

Triazolam differs from alprazolam primarily at the 6-phenyl substituent:

Drug	6-position substituent	8-position substituent	1-position substituent
Alprazolam	Phenyl	Chlorine	Methyl
Triazolam	2-chlorophenyl	Chlorine	Methyl

Claim 12 is narrower than claim 1 because it specifies each material substituent. The patent’s expiration means that claim 12 no longer prevents generic triazolam production. Later regulatory or formulation patents would need to be analyzed separately.

What is the scope of claim 1 compared with claims 2 through 15?

Claim 1 is the broad genus claim. Claims 2 through 15 are species claims directed to particular members of the genus.

The claim hierarchy has several legal consequences:

A compound may infringe claim 1 without being one of the specifically named compounds in claims 2 through 15.
A listed species can potentially fall within both claim 1 and its corresponding dependent claim.
If a court invalidated a species claim but upheld claim 1, the species could remain covered by the genus claim.
If claim 1 were invalidated for lack of enablement, written description, anticipation, or obviousness, the dependent claims would require separate analysis.
The salt language extends protection beyond the neutral free-base compounds to pharmacologically acceptable acid-addition salts.

The genus is broad in substituent coverage but chemically constrained. It does not claim all benzodiazepines, all triazolobenzodiazepines, or all anxiolytic compounds. The 6-phenyl triazolobenzodiazepine framework is central to infringement analysis.

When did US Patent 3,987,052 expire?

US Patent 3,987,052 was granted on October 19, 1976. Because it was filed and granted under the pre-Uruguay Round patent-term system, the ordinary term was generally 17 years from grant rather than 20 years from the earliest effective U.S. filing date.

Event	Date or period
Patent grant	October 19, 1976
Ordinary 17-year term from grant	October 19, 1993
Current status	Expired
Current blocking effect	None from this patent

The patent’s expiration predates the modern patent-term-adjustment system introduced by the Uruguay Round Agreements Act. Patent term should be confirmed against the official USPTO record for any litigation-grade opinion, but the patent is not an active U.S. right. [1][4]

What is the Orange Book status of alprazolam and triazolam?

US Patent 3,987,052 is not a current Orange Book patent barrier because it expired decades ago.

The FDA Orange Book identifies patents and regulatory exclusivities associated with approved drug products. Expired patents may remain visible in historical records, but they do not prevent ANDA approval or generic launch after expiration. Current Orange Book analysis must be performed at the product level because different products may have different:

Approved dosage forms.
Sponsors.
Formulation patents.
Method-of-use patents.
Pediatric exclusivity periods.
Patent certifications.
Regulatory exclusivity dates.

For immediate-release alprazolam tablets, the relevant practical barrier is the expired compound patent. Extended-release alprazolam products, including Xanax XR-type products, require a separate review of later formulation and dosage-form patents. The same distinction applies to immediate-release and modified-release triazolam products. [2][3]

What formulation patents protect alprazolam after the compound patent expired?

Later patent activity involving alprazolam generally falls into four categories:

Immediate-release tablets

Immediate-release alprazolam tablets rely on the known active ingredient and conventional excipients. After expiration of the compound patent, generic manufacturers can generally pursue ANDAs using bioequivalence and pharmaceutical-equivalence standards.

Extended-release alprazolam

Extended-release products may have separate protection directed to:

Controlled-release matrices.
Multiparticulate systems.
Release-controlling polymers.
Tablet manufacturing processes.
Dissolution profiles.
Once-daily administration.
Pharmacokinetic performance.

These patents do not revive the expired compound patent. They may, however, affect a specific dosage form or product presentation.

Orally disintegrating and alternative dosage forms

Later patents may cover orally disintegrating tablets, rapidly dissolving compositions, taste masking, or other dosage-form technologies. Such claims are narrower than a compound claim and generally require the accused product to practice the specified formulation limitations.

Combination and method-of-use patents

A later patent may claim alprazolam in combination with another active ingredient or for a particular treatment method. These claims are distinct from the broad chemical claims in US 3,987,052 and are assessed under separate infringement and validity standards.

Were there Paragraph IV challenges to US Patent 3,987,052?

A current Paragraph IV challenge to US Patent 3,987,052 is no longer commercially relevant because the patent expired in 1993. Paragraph IV certification is used when an ANDA applicant asserts that a listed patent is invalid, unenforceable, or will not be infringed. After expiration, an applicant normally does not need to challenge the patent to obtain approval based on that patent.

Generic alprazolam competition therefore shifted from patent invalidity litigation to ordinary ANDA approval, bioequivalence, manufacturing capacity, controlled-substance compliance, and commercial pricing.

Historical ANDA litigation involving alprazolam may have concerned later patents, product-specific listings, or other rights. It should not be attributed to US 3,987,052 without a case-specific docket or Orange Book record.

Which companies challenged the alprazolam patent estate?

The original patent owner was The Upjohn Company, associated with development and commercialization of Xanax. Upjohn later became part of Pharmacia, which was acquired by Pfizer.

The competitive field after compound-patent expiration included multiple generic manufacturers filing ANDAs for alprazolam tablets and related dosage forms. The existence of a generic filing does not, by itself, establish a Paragraph IV challenge to US 3,987,052. The patent had already expired when much of the modern generic market developed.

The commercially relevant company groups were:

Company group	Role
The Upjohn Company	Original patent owner and originator associated with Xanax
Pharmacia/Pfizer	Successor corporate interests and branded-product commercialization
Generic ANDA sponsors	Manufacturers of alprazolam products after patent expiration
Contract manufacturers	API and finished-dose suppliers subject to separate manufacturing and quality controls

How strong is the patent estate for the claimed compounds?

The historical estate was strong in one respect and limited in another.

Strengths

Claim 1 covered a broad chemical genus.
Claim 2 specifically identified alprazolam.
Claim 12 specifically identified triazolam.
Composition claims generally provide stronger exclusivity than method-of-use claims.
The salt language covered clinically relevant pharmaceutical forms.
The patent reached multiple substituted analogs within one claim structure.

Limitations

The patent expired in 1993.
It does not protect later formulations unless those formulations inherently practice the claimed compound, which would not matter after expiration.
It does not establish current protection for extended-release, orally disintegrating, or combination products.
Its broad genus could have faced enablement, written-description, anticipation, or obviousness challenges if litigated during its term.
The patent’s commercial value was concentrated in a limited number of compounds, especially alprazolam and triazolam.

The current patent strength of US 3,987,052 is therefore zero as an exclusionary right, although its historical importance remains high as an early composition patent.

What generic launch risks exist for alprazolam?

For standard immediate-release alprazolam, the expired compound patent presents no current launch risk. The principal risks are operational and regulatory:

FDA bioequivalence failure.
Controlled-substance manufacturing and distribution requirements.
Drug-supply interruptions.
Active pharmaceutical ingredient qualification.
Current Good Manufacturing Practice compliance.
Product-specific formulation patents.
Labeling differences.
State substitution rules.
Market concentration and price erosion.

For extended-release alprazolam, a generic applicant must assess later patents covering release characteristics and dosage-form design. A product may avoid infringement of a formulation patent by using a different release mechanism, but that determination requires claim-chart analysis against the actual product and manufacturing process.

Are biosimilar risks relevant to this patent?

No. Alprazolam and triazolam are small-molecule chemical drugs, not biologics. Biosimilar pathways under the Public Health Service Act do not apply.

The relevant FDA pathway is the ANDA route under section 505(j) of the Federal Food, Drug, and Cosmetic Act. Generic applicants must establish pharmaceutical equivalence and bioequivalence to the listed reference product, subject to product-specific FDA requirements. [2][5]

What manufacturing and geographic IP barriers remain?

US Patent 3,987,052 creates no current geographic barrier in the United States. The corresponding international patent landscape must be assessed country by country because:

Patent terms differ by jurisdiction.
Foreign counterparts may have different claims.
National-phase prosecution may have narrowed the claims.
Some foreign rights may have expired earlier or later.
Supplementary protection certificates generally apply to eligible medicinal products in certain jurisdictions, not uniformly.
Regulatory exclusivity and patent rights may have different durations.

Manufacturing barriers may still exist without active compound patents. These include controlled-substance registration, API sourcing, process validation, impurity control, and FDA inspection readiness. Those barriers are commercial and regulatory rather than rights created by US 3,987,052.

What is the revenue exposure associated with this patent?

The patent’s historical revenue exposure was concentrated in branded Xanax and Halcion-related products and in the broader commercial value of the claimed triazolobenzodiazepine platform.

The patent no longer supports royalty revenue or exclusionary pricing in the United States. Current revenue exposure depends on later rights and product formats:

Product category	Exposure to US 3,987,052 today
Immediate-release alprazolam	None
Generic alprazolam tablets	None
Immediate-release triazolam	None
Extended-release alprazolam	Only through later patents, if any
Combination products	Only through later combination or method patents
Foreign products	Depends on national patent status
API manufacturing	No current exclusion from this patent

Key Takeaways

US Patent 3,987,052 is a broad triazolobenzodiazepine composition patent.
Claim 2 specifically covers alprazolam.
Claim 12 specifically covers triazolam.
Claim 1 covers a genus of substituted 6-phenyl triazolobenzodiazepines and acid-addition salts.
The patent was granted October 19, 1976, and ordinarily expired October 19, 1993.
It is not a current U.S. barrier to generic alprazolam or triazolam.
Paragraph IV challenges to this patent are no longer commercially material.
Biosimilar analysis is irrelevant because the products are small-molecule drugs.
Later formulation, extended-release, combination, and method-of-use patents require separate analysis.
Current launch risk is primarily regulatory, manufacturing, supply-chain, and product-specific rather than based on US 3,987,052.

FAQs

Does US Patent 3,987,052 cover Xanax?

Yes. Claim 2 specifically covers alprazolam, the active ingredient in Xanax. The patent has expired.

Does US Patent 3,987,052 cover Halcion?

Yes. Claim 12 identifies triazolam, the active ingredient in Halcion. The patent has expired.

Can a generic manufacturer launch alprazolam without a license from Upjohn or Pfizer?

Yes, with respect to US Patent 3,987,052. The patent no longer requires a license. The manufacturer must still satisfy FDA approval, manufacturing, controlled-substance, and product-specific patent requirements.

Are alprazolam salts covered by the patent?

Yes. Claim 1 expressly includes pharmacologically acceptable acid-addition salts of the claimed compounds.

Does the patent cover all benzodiazepines?

No. It covers a defined triazolobenzodiazepine structure with a 6-phenyl substituent and specified substituent classes. Other benzodiazepine structures fall outside the claim unless they independently satisfy the claim limitations.

References

United States Patent and Trademark Office. (1976). Triazolobenzodiazepines (U.S. Patent No. 3,987,052).
U.S. Food and Drug Administration. (2024). Drugs@FDA: FDA-approved drugs database.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations (Orange Book).
United States Patent and Trademark Office. (2024). Patent examination and patent term information.
Federal Food, Drug, and Cosmetic Act, 21 U.S.C. § 355.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Australia	490626	⤷ Start Trial
Australia	491139	⤷ Start Trial
Belgium	747493	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 3,987,052

Summary for Patent: 3,987,052