United States Drug Patent 4,800,191: Claim Scope, Expiration, and GnRH Antagonist Patent Landscape

US Patent No. 4,800,191 covers a defined class of synthetic peptide antagonists of gonadotropin-releasing hormone, or GnRH, together with protected peptide intermediates, pharmaceutical compositions, and methods for reducing pituitary gonadotropin availability. The patent issued on January 24, 1989. Assuming no later term adjustment or unusual terminal disclaimer, its ordinary 17-year patent term expired on January 24, 2006. The patent therefore does not create a current blocking right.

The claims are directed principally to peptide sequence architecture, stereochemistry, side-chain substitutions, N-terminal acylation, C-terminal amidation, and protected synthetic intermediates. They do not cover every GnRH antagonist, every peptide containing a GnRH-antagonist motif, or later small-molecule GnRH antagonists such as relugolix, elagolix, or fezolinetant.

What does US Patent 4,800,191 protect?

US 4,800,191 protects three related subject-matter groups:

Finished peptide compounds with a specified backbone and substituted amino acids.
Protected peptide forms and resin-bound intermediates used in chemical synthesis.
Pharmaceutical compositions and therapeutic methods using the claimed finished peptides to reduce pituitary gonadotropin availability.

The central finished-peptide structure is:

X-R1-R2-R3-Ser-Tyr-R6-Leu-Arg-Pro-R10-NH2

The key structural restrictions are:

Element	Claimed requirement
X	Acyl group derived from a straight-chain, branched-chain, or alicyclic carboxylic acid having 1-7 carbon atoms
R1	Selected D- or L-Pro, Δ3-Pro, D-Phe, halogenated D-Phe, D-Ser, D-Thr, D-Ala, D-Nal(1), or D-Nal(2)
R2	D-Phe or halogenated D-Phe
R3	D-Trp, D-Phe, D-Pal, D-Nal(1), or D-Nal(2)
R6	D-Cit, D-Hci, or lower-alkyl-substituted analogs
R10	Gly or D-Ala
C terminus	Amide, shown as `-NH2`
Salt form	Pharmaceutically acceptable acid-addition salts

The claim set is therefore a Markush genus. Infringement would require a product to fall within every applicable limitation, including sequence position, stereochemistry, side-chain identity, terminal groups, and any dependent-claim restrictions.

How broad is claim 1 of US 4,800,191?

Claim 1 is the principal compound claim and has broad combinatorial scope within a narrow chemical framework.

Its breadth comes from the number of permitted alternatives at R1, R2, R3, R6, and R10. Its limitations come from the fixed positions of Ser, Tyr, Leu, Arg, and Pro, the required C-terminal amide, and the specified D-amino-acid configuration.

Claim 1 scope by variable position

The approximate substitution universe is large:

R1 has at least 14 expressly listed alternatives, depending on how the halogenated phenylalanine and naphthylalanine entries are counted.
R2 has two principal alternatives.
R3 has five principal alternatives.
R6 has four expressly described categories, including D-Cit, D-Hci, and lower-alkyl variants.
R10 has two alternatives.

A simple multiplication of listed options produces more than 1,000 theoretical combinations before accounting for chemical validity, claim interpretation, enablement, written description, and examples in the specification.

The claim does not cover arbitrary substitutions. A peptide with L-Trp at R3, a non-amidated C terminus, or a different backbone residue at the fixed Ser, Tyr, Leu, Arg, or Pro positions would not literally satisfy claim 1.

What do claims 2 and 6-16 add?

Claims 2 and 6-16 progressively narrow the compound genus.

Claim 2 limits:

R1 to Pro, D-Phe, D-Phe(4-Cl), or D-Nal(2);
R2 to D-Phe(4-F) or D-Phe(4-Cl); and
R3 to D-Trp.

Claim 6 requires acetylation at the N terminus. Claims 7-10 then select specific R1 residues:

Claim	Principal narrowing
6	Claim 2 compound with X as acetyl
7	R1 is Pro
8	R1 is D-Nal(2)
9	R1 is D-Phe(4-Cl)
10	R1 is D-Phe
11-12	Claim 7 with D-Cit, D-Cit(Et), D-Hci, or D-Hci(Et)
13	Claim 8 with D-Hci or D-Cit
14	Claim 9 with D-Hci or D-Cit
15-16	Claim 10 with D-Cit, D-Cit(Et), D-Hci, or D-Hci(Et)

These dependent claims are commercially more important than the broad genus if a marketed peptide corresponds to one of the specifically selected sequences. They provide narrower fallback positions if claim 1 is challenged for lack of enablement, written description, anticipation, or obviousness.

What are claims 3-5 directed to?

Claims 3-5 cover protected peptide intermediates and synthesis forms rather than only finished pharmacologically active peptides.

Claim 3 covers a structure containing:

Protected or unprotected Ser;
Protected or unprotected Tyr;
D-Lys or D-Orn at the R6 position;
Protected or unprotected Arg;
A C-terminal hydrogen or resin support;
A benzhydryl or methylbenzhydryl resin option;
N-terminal acyl, t-Boc, or hydrogen forms subject to protection conditions.

The listed protecting groups include:

Functional site	Listed protection
Ser hydroxyl	2,6-dichlorobenzyl and related options
Tyr phenol	Benzyl, bromobenzyloxycarbonyl-related protection, or 2,6-dichlorobenzyl
Lys or Orn side chain	Z(2-Cl) or hydrogen
Arg guanidino group	Nitro, Tos, methyl-(t-butylbenzyl)sulfonyl, or 4-methoxy-2,3,6-trimethylbenzylsulfonyl
C terminus	Benzhydryl or methylbenzhydryl resin support

These claims are relevant to manufacturing-IP analysis. A competing manufacturer could avoid literal infringement by using a different protecting-group strategy, a different resin, a different order of assembly, or a solution-phase process, depending on the complete claim language and prosecution history.

The supplied text contains apparent transcription inconsistencies, including the transition between D-Lys/D-Orn in claim 3 and D-Cit/D-Hci in claim 1, as well as notation such as R.*6 and Q2. The issued patent and prosecution history control the legal interpretation.

What do claims 17-19 protect?

Claims 17-19 add pharmaceutical and therapeutic coverage.

Claim 17 covers a pharmaceutical composition containing:

A compound of claim 1; and
A pharmaceutically acceptable carrier.

Claim 18 covers administering a claim 1 compound to reduce the physiological availability of pituitary gonadotropins in a mammal.

Claim 19 limits the method to a daily dose of 0.1 to 2.5 mg/kg body weight.

These claims are narrower than a general method of treating hormone-sensitive disease. They require use of a claim 1 compound and target the physiological availability of pituitary gonadotropins. A method using a later small-molecule GnRH antagonist would not fall within these claims because the active ingredient would not be a compound of claim 1.

When did US 4,800,191 lose exclusivity?

Event	Date or consequence
Patent issued	January 24, 1989
Pre-URAA patent term	17 years from issue
Ordinary expiration	January 24, 2006
Current status	Expired; no enforceable patent exclusion based on ordinary term
Orange Book effect	Expired patent cannot block a current generic launch

US 4,800,191 was granted under the pre-Uruguay Round Agreements Act patent-term regime. For patents filed before June 8, 1995, the applicable term generally was the longer of 17 years from grant or 20 years from the earliest effective nonprovisional filing date. For a patent issued in 1989, the 17-year-from-grant calculation ordinarily controls unless a specific adjustment, disclaimer, or unusual prosecution event changed the term. [1]

Patent expiration does not eliminate other possible rights. Later patents could cover a particular formulation, depot system, manufacturing process, salt, indication, dosing schedule, or approved product. Those later rights must be analyzed separately.

What is the Orange Book status of US 4,800,191?

US 4,800,191 itself is not a current exclusivity barrier in the FDA Orange Book because it expired in 2006. The Orange Book lists patents submitted by sponsors for approved drug products, not every patent historically associated with a chemical class. [2]

The claim text alone does not establish that a specific approved product was listed under this patent. Orange Book analysis requires matching:

The approved active ingredient;
The NDA holder;
The listed patent number;
The dosage form or formulation;
Any method-of-use code;
The patent expiration date.

GnRH antagonist products approved in the United States include peptide products such as degarelix and oral small molecules such as relugolix and elagolix. Their current patent positions arise primarily from later product-specific estates, not from the expired claims of US 4,800,191.

Which drugs are technically closest to the claimed peptides?

The patent is technically closest to peptide GnRH antagonists, particularly compounds having substituted amino acids, D-amino-acid residues, N-terminal acylation, and C-terminal amidation.

Product or class	Active ingredient	Relationship to US 4,800,191
Cetrorelix	Peptide GnRH antagonist	Same broad therapeutic class; literal coverage requires sequence-level correspondence
Ganirelix	Peptide GnRH antagonist	Same class; not automatically covered by a genus claim unless every limitation is met
Degarelix	Long-acting peptide GnRH antagonist	Later peptide architecture and depot formulation; requires separate claim comparison
Leuprolide	GnRH agonist peptide	Pharmacologically related but not an antagonist and not automatically within the claims
Relugolix	Nonpeptide GnRH antagonist	Outside the peptide compound claims
Elagolix	Nonpeptide GnRH antagonist	Outside the peptide compound claims
Abarelix	Peptide GnRH antagonist	Requires sequence and terminal-group comparison

A class-level label such as "GnRH antagonist" is not enough to establish infringement. The decisive analysis is a residue-by-residue comparison, including stereochemistry and terminal chemistry.

How does the patent compare with later GnRH antagonist patents?

US 4,800,191 is an early composition-of-matter patent centered on peptide sequence variation. Later patent estates generally use one or more of five strategies:

Later patent strategy	Typical protected subject matter
New peptide sequence	Alternative residue pattern with improved potency or tolerability
Long-acting formulation	Injectable depot, polymer matrix, or sustained-release composition
Manufacturing process	Solid-phase synthesis, purification, impurity control, or scale-up
Clinical use	Infertility, endometriosis, uterine fibroids, prostate cancer, or controlled ovarian stimulation
Small-molecule chemistry	Oral nonpeptide GnRH receptor antagonists and their salts or formulations

The older patent may be relevant as prior art against later peptide claims, but its expiration does not remove its prior-art effect. A later patent cannot restore exclusivity to the expired sequence claims. A later patent can still protect a new formulation, process, or therapeutic use if the statutory requirements are met.

What Paragraph IV risks exist?

A Paragraph IV certification concerns patents listed in the Orange Book for an approved drug product. Because US 4,800,191 expired decades ago, it would not ordinarily support a current Paragraph IV challenge.

For a current peptide GnRH antagonist, the relevant risks are:

A listed composition-of-matter patent covering the exact active peptide.
A formulation patent covering a depot or injectable presentation.
A method-of-use patent covering the proposed indication.
A process patent that may create manufacturing litigation risk, even if it does not block approval.
Pediatric exclusivity or other regulatory exclusivity attached to a current listed patent.

A generic or follow-on applicant would need to compare its active peptide and product presentation against the current Orange Book listings for the reference product. FDA approval does not require resolution of every non-listed patent.

Are biosimilar issues relevant?

Biosimilar risk is limited for this patent because US 4,800,191 claims synthetic peptides, not biologics licensed under the Public Health Service Act. FDA approval of a follow-on peptide would generally proceed through the drug application framework rather than the biosimilar pathway.

A peptide product can still face regulatory complexity involving:

Active-ingredient identity;
Stereochemical purity;
Sequence confirmation;
Aggregates and degradation products;
Synthetic impurities;
Immunogenicity;
Bioequivalence or clinical bridging.

Those issues affect approval and substitutability but do not convert the patent into a biologic patent.

What patent litigation and settlements affect US 4,800,191?

The patent text does not establish litigation, a Paragraph IV filing, or a settlement agreement. Because the patent expired in 2006, any current litigation exposure would have to arise from later patents or from a dispute over historical damages, ownership, inventorship, or term calculation.

An expired patent can remain relevant in historical disputes involving:

Pre-expiration sales;
Patent ownership;
License royalties;
Contractual covenants;
Audit rights;
Antitrust or licensing claims;
Patent misuse allegations.

It cannot support a new ordinary infringement suit for conduct occurring after expiration.

How strong is the patent estate for a commercial product?

The strength of US 4,800,191 alone is low for current commercial exclusivity because its term has ended. Its historical strength was higher where a product matched the specific peptide genus and where claims 6-16 captured acetylated, amidated compounds with the specified D-amino-acid substitutions.

Risk factor	Assessment
Core composition claims	Expired
Dependent sequence claims	Expired
Protected-intermediate claims	Expired
Composition claims	Expired
Method claims	Expired
Current generic blocking power	None from this patent
Prior-art value	Remains relevant
Manufacturing relevance	Historical; later process patents may matter
Biosimilar relevance	Limited
Orange Book relevance	No current blocking effect
Revenue exposure	No current revenue can be attributed solely to this patent

What geographic coverage did the patent provide?

US 4,800,191 provided rights only in the United States. International protection would require separate national or regional patents based on the relevant priority and filing history.

A US patent does not automatically establish protection in:

Europe;
Japan;
Canada;
China;
Australia;
India;
Latin America.

Foreign family members may have had different claims, prosecution outcomes, expiration dates, and legal status. A global freedom-to-operate analysis therefore cannot rely on the US patent number alone.

Key Takeaways

US 4,800,191 covers a genus of synthetic peptide GnRH antagonists with defined residues, stereochemistry, acyl groups, side-chain substitutions, and C-terminal amidation.
Claims 1, 2, and 6-16 are the principal finished-compound claims.
Claims 3-5 cover protected intermediates and resin-bound synthesis forms.
Claims 17-19 cover pharmaceutical compositions and methods for reducing pituitary gonadotropin availability.
The patent issued January 24, 1989, and ordinarily expired January 24, 2006.
The patent has no current generic-blocking or Orange Book exclusivity value.
Later GnRH antagonist products require sequence-specific comparison; therapeutic class similarity alone does not establish coverage.
Current commercial risk is more likely to arise from later formulation, manufacturing, method-of-use, or product-specific patents.
The patent may remain relevant as prior art and in historical licensing or damages disputes.
It provides US coverage only; foreign family rights require separate analysis.

FAQs About US Patent 4,800,191

Does US 4,800,191 cover cetrorelix?

Not automatically. Cetrorelix would require a residue-by-residue comparison against the claimed formula, including each variable position, D/L configuration, N-terminal group, C-terminal amide, and applicable dependent limitations.

Does US 4,800,191 cover ganirelix?

The same sequence-specific analysis applies. Ganirelix is a peptide GnRH antagonist, but the therapeutic class does not determine literal claim coverage.

Can an expired peptide patent still block FDA approval?

It cannot create a current patent-based block after expiration. FDA review may still consider product quality, identity, safety, efficacy, and bioequivalence. Later patents may create separate commercial barriers.

Does a patent on a GnRH antagonist cover its use in prostate cancer?

Only if the method claim covers the specific active compound, patient population, disease, dosing regimen, and other required limitations. Claims 18-19 are directed to reducing pituitary gonadotropin availability and do not expressly recite prostate cancer.

Are protected peptide intermediates commercially relevant after patent expiration?

They can remain relevant as historical prior art and as part of a freedom-to-operate review of later manufacturing patents. They do not create current exclusivity after the patent term ends.

References

United States Patent and Trademark Office. (2024). Patent term adjustment and patent term provisions. U.S. Department of Commerce.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book. U.S. Department of Health and Human Services.
United States Patent and Trademark Office. (1989). U.S. Patent No. 4,800,191.
U.S. Food and Drug Administration. (2024). Purple Book: Database of licensed biological products. U.S. Department of Health and Human Services.
Food and Drug Administration. (2024). Abbreviated new drug application and patent certification requirements. 21 U.S.C. § 355(j).

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
European Patent Office	0299402	⤷ Start Trial	C990029	Netherlands	⤷ Start Trial
European Patent Office	0299402	⤷ Start Trial	099C0031	Belgium	⤷ Start Trial
European Patent Office	0299402	⤷ Start Trial	31/1999	Austria	⤷ Start Trial
Austria	90362	⤷ Start Trial
Brazil	1100478	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,800,191

Summary for Patent: 4,800,191