US Patent 5,512,570: Scope, Claims, Expiration, and Patent Landscape for Neurokinin-1 Antagonists

US Patent 5,512,570 protected methods for treating or preventing emesis using a broad genus of morpholine-linked neurokinin-1, or NK1, receptor antagonists and selected phosphate, sulfonate, succinate, and prodrug derivatives. The claims also covered specific triazolone-containing compounds associated with the aprepitant and fosaprepitant development program. The patent has expired. Its estimated US term ended in November 2013, subject to the patent’s recorded term calculation and any applicable adjustment. It does not present a current blocking right against generic aprepitant, fosaprepitant, or other NK1-antagonist development.

The patent remains important as a historical priority document because it discloses and claims structural classes that include pharmaceutical antiemetic candidates, including phosphorylated derivatives designed to improve water solubility and parenteral administration.

What does US Patent 5,512,570 cover?

US Patent 5,512,570 is directed to methods for treating or preventing emesis in mammals through administration of compounds represented by a large Markush formula. The disclosed chemistry is centered on substituted morpholine systems connected to nitrogen-containing heterocycles, including triazolone-type rings.

The claims cover several related subject-matter categories:

Claim category	Claims	Principal scope
Broad method genus	1	Administration of formula I compounds or pharmaceutically acceptable salts for emesis
Restricted substituent genus	2-11	Narrower R-group, linker, heterocycle, and prodrug definitions
Named compounds	12-13	Seven specifically identified compounds and bis(N-methyl-D-glucamine) salts
Structural compound group	14-15	Specific illustrated compounds and counterions, including N-methyl-D-glucamine

The patent claims methods rather than a free-standing composition or compound claim. That distinction matters. A product claim would directly target manufacture, sale, or use of a compound. These claims require proof that the accused product is administered for treatment or prevention of emesis, or that another claim theory applies.

How broad is claim 1 of US 5,512,570?

Claim 1 is a broad method-of-use claim with extensive structural alternatives. It requires:

A mammal in need of treatment or prevention of emesis.
Administration of an effective amount.
A compound of formula I or a pharmaceutically acceptable salt.
Compliance with the defined substituent options for R2, R3, R6-R8, R11-R13, A, B, X, Y, Z, and p.

The claim’s breadth derives from several independent variable regions.

R2 and R3 substitution

R2 and R3 may independently include:

Hydrogen;
C1-C6 alkyl;
C2-C6 alkenyl;
C2-C6 alkynyl;
Phenyl; or
Joined carbocyclic or heterocyclic rings.

The substituent lists include hydroxy, oxo, alkoxy, phenylalkoxy, cyano, halo, amino, amide, carbamate, ketone, and ester groups. R2 and R3 may also combine to form cyclopentyl, cyclohexyl, phenyl, pyrrolidinyl, piperidinyl, pyrrolyl, pyridinyl, imidazolyl, furanyl, oxazolyl, thienyl, or thiazolyl systems.

This creates a large genus extending well beyond a single commercial molecule.

R6-R8 and R11-R13 substitution

R6, R7, and R8 have broad hydrocarbon, aromatic, halogen, cyano, nitro, trifluoromethyl, sulfur, amino, hydroxy, alkoxy, carbonyl, pyridyl, tetrazolyl, oxazolyl, and thiazolyl definitions.

R11, R12, and R13 may use the R6-R8 definitions or be linked to -OX. These positions are significant because they permit incorporation of phosphate, sulfonate, succinate, and related solubilizing groups.

The A-B framework

A may be:

C1-C6 alkyl;
C2-C6 alkenyl; or
C2-C6 alkynyl,

with extensive optional substitution.

B is a heterocycle selected from the structures shown in the patent. The claims permit further substitution with alkyl, alkoxy, oxo, hydroxy, thioxo, thioether, halo, cyano, phenyl, trifluoromethyl, aminoalkyl, amide, ester, or alkoxyalkyl groups.

Claims 6-8 narrow this portion by selecting specific B structures or defined A-B combinations.

X: solubilizing groups and prodrug linkages

X is one of the most commercially relevant portions of the claim. It includes:

Phosphate mono- and dianions;
Phosphonate-containing groups;
Sulfonate groups;
Hemisuccinate-type groups;
Hydroxyethylamine-associated salts;
A substituted carbonate or carbamate-type group;
Hydrogen, subject to the claim proviso.

These alternatives indicate a strategy of claiming both active NK1-antagonist structures and water-solubilizing derivatives. Phosphate salts are particularly relevant to fosaprepitant, the injectable prodrug of aprepitant.

Y and Z

Y may be a bond, oxygen, sulfur, carbonyl, methylene, substituted methylene, or substituted carbon. Z may be hydrogen, C1-C6 alkyl, or hydroxy, with restrictions where Y is oxygen or a substituted methylene.

The Y-Z limitations control the connection between the aromatic or heterocyclic portions of the molecule and help define the stereochemical and functional relationships in the claimed compounds.

What do claims 2 through 11 add?

Claims 2 through 11 progressively narrow the Markush genus.

Claim	Narrowing feature
2	Restricts R2/R3 to hydrogen, alkyl, alkenyl, or phenyl; limits R6-R8 and R11-R13; selects particular heterocycles and phosphate or prodrug groups
3	Requires Z to be C1-C4 alkyl
4	Requires Z to be methyl
5	Limits A to methylene or substituted methylene
6	Selects particular B heterocycles
7	Selects defined A-B combinations
8	Selects additional A-B combinations
9	Selects phosphate, diammonium, and aminoalkyl carbonate or ester derivatives
10	Uses structural formula II
11	Uses structural formula III

Claims 3-9 are narrower fallback positions. They reduce the number of possible structures but remain method claims. A compound that falls within claim 9, for example, would still need to be administered for treatment or prevention of emesis to satisfy the claim as written.

Which compounds are specifically identified in claim 12?

Claim 12 recites seven named compounds. The compounds generally share the following structural features:

A substituted morpholine core;
A 3,5-bis(trifluoromethyl)phenyl-containing side chain;
A phenyl or 4-fluorophenyl substituent;
A 1,2,4-triazolone or related triazole heterocycle;
One or more phosphoryl or phosphonate groups in several examples;
Defined stereochemistry at the morpholine and side-chain centers.

The named compounds include phosphorylated derivatives identified by the position of phosphorylation on the triazolone ring. Claims 13 and 15 focus on salts involving N-methyl-D-glucamine, also known as meglumine.

This is consistent with a prodrug-development strategy: the parent NK1 antagonist has limited aqueous solubility, while phosphate or related derivatives can be formulated for injection after conversion in vivo to the active antagonist.

Does US 5,512,570 claim aprepitant or fosaprepitant directly?

The patent’s claims may read on structural embodiments related to aprepitant and fosaprepitant, but the supplied text does not include the structural drawings needed to make a definitive chemical identity determination for every claim 12 or 14 embodiment.

The commercial relationship is nevertheless clear:

Aprepitant is an orally active NK1 receptor antagonist marketed as Emend.
Fosaprepitant is a phosphorylated water-soluble prodrug of aprepitant marketed for intravenous use, including as Emend for Injection and later products.
The patent claims phosphate derivatives and includes bis(N-methyl-D-glucamine) salt language that is consistent with injectable prodrug chemistry.

The most commercially important blocking rights for branded aprepitant and fosaprepitant were not limited to US 5,512,570. Later patents directed specifically to aprepitant, fosaprepitant, formulations, methods of use, and manufacturing were more relevant to regulatory and litigation positions.

When did US Patent 5,512,570 expire?

The patent was issued on April 30, 1996. Its US application was filed in 1993, and the patent term is governed principally by the 20-year term measured from the earliest relevant US nonprovisional filing date under the post-Uruguay Round patent-term rules.

The estimated ordinary expiration date was in November 2013. Any patent-term adjustment would have been added to the base term, but the patent is no longer enforceable.

Event	Date or status
US application filing	1993
Patent issued	April 30, 1996
Estimated ordinary expiration	November 2013
Current enforceability	Expired
Current Orange Book blocking effect	None

The patent’s expiration eliminates current infringement exposure under its method claims. Historical infringement, damages, and questions concerning past conduct are separate issues subject to limitation periods, prosecution history, and applicable litigation facts.

What is the Orange Book status of US 5,512,570?

US 5,512,570 should not be treated as a current Orange Book barrier for Emend, fosaprepitant, or generic aprepitant products.

FDA Orange Book listings for a reference product can include patents covering:

The active ingredient;
A drug product or formulation;
A method of use;
A dosage form or route of administration.

The Orange Book status of an individual patent must be evaluated by product and listing history. Expired patents do not provide a current basis for blocking FDA approval or commercial launch. Later Emend-related patents, rather than US 5,512,570, controlled the principal historical Hatch-Waxman timetable.

What is the broader aprepitant and fosaprepitant patent landscape?

The relevant landscape contains several patent families rather than one controlling patent.

Patent subject	Commercial relevance
Broad NK1-antagonist genus	Early chemical and method-of-use protection
Specific aprepitant compounds	Core active-ingredient protection
Fosaprepitant phosphate prodrug	Injectable and solubility-improved product protection
Formulation patents	Oral capsules, injectable solutions, excipients, and stability
Method-of-use patents	Chemotherapy-induced nausea and vomiting, postoperative nausea and vomiting
Manufacturing patents	Stereoselective synthesis, intermediates, purification, and salt formation
Regulatory patents	Orange Book-listed methods or drug-product claims

The commercial patent estate for aprepitant was stronger than US 5,512,570 alone because later filings addressed the specific clinical product and its pharmaceutical forms.

What patent litigation and Paragraph IV activity affected aprepitant?

Generic aprepitant development generated Hatch-Waxman activity involving challenges to later Merck patents. Paragraph IV certifications commonly targeted patents covering the specific aprepitant product, formulation, or approved method rather than an expired early genus patent.

The legal significance of US 5,512,570 in such proceedings was limited:

An expired patent cannot trigger the 30-month stay under 21 U.S.C. § 355(j)(5)(B)(iii).
An expired method claim cannot independently block an ANDA approval.
A generic applicant could rely on the absence of enforceable rights under this patent while addressing any later unexpired Orange Book patents.
Safe-harbor activities under 35 U.S.C. § 271(e)(1) further protect activities reasonably related to FDA submission.

The relevant litigation analysis therefore requires a product-specific review of later patents, their expiration dates, terminal disclaimers, certifications, settlements, and launch provisions. US 5,512,570 is not the operative litigation patent today.

Which companies challenged or competed with the aprepitant estate?

The competitive field included generic manufacturers and alternative NK1-antagonist developers.

Generic manufacturers

Generic companies that entered or pursued aprepitant opportunities included major ANDA sponsors such as Teva, Mylan, Sandoz, Dr. Reddy’s Laboratories, and other suppliers. The precise challenger set varied by dosage form, strength, product, and filing date.

Competing branded NK1 antagonists

Product	Active ingredient	Sponsor or principal developer	Competitive position
Emend	Aprepitant	Merck	Oral NK1 antagonist
Emend for Injection	Fosaprepitant	Merck	Intravenous prodrug
Varubi	Rolapitant	Tesaro, later GSK-related commercial ownership	Long-acting NK1 antagonist
Akynzeo	Netupitant plus palonosetron	Helsinn and partners	Fixed combination antiemetic
Cinvanti	Aprepitant injectable emulsion	Heron Therapeutics	Injectable aprepitant formulation

These products relied on distinct patent estates. A competitor’s freedom to operate could not be assessed solely against US 5,512,570.

How strong was the patent estate under US 5,512,570?

As an issued patent, the claims had substantial historical breadth. The estate’s strongest features were:

Broad chemical genus language;
Multiple fallback claims;
Specific named compounds;
Phosphate and salt alternatives;
Method claims tied to a commercially important antiemetic indication;
Coverage of potential injectable prodrug forms.

The principal limitations were:

The claims are method claims, not direct composition claims;
The broad Markush language creates potential written-description and enablement pressure;
The supplied claim text omits key structural drawings;
The claim requires administration for emesis;
The patent has expired.

For current business decisions, enforceability is the controlling factor. The patent has no present blocking strength. Its historical value is as an early disclosure and priority document in the NK1-antagonist and prodrug patent family.

What manufacturing and formulation barriers remain after expiration?

Expiration of this patent does not eliminate all technical barriers. Commercial entrants may still face:

Control of stereochemistry in the morpholine core;
Reproducible synthesis of the triazolone-containing intermediate;
Phosphate salt isolation and polymorph control;
Hydrolysis and stability management for fosaprepitant;
Injectable formulation compatibility;
Residual solvent and impurity limits;
Bioequivalence requirements for oral products;
Comparative pharmacokinetic or clinical requirements for injectable products.

These are regulatory and manufacturing barriers, not continuing rights under US 5,512,570. Any surviving patent risk would arise from later patents covering a particular formulation, process, impurity profile, dosage regimen, or approved method.

What generic launch scenarios exist?

For US 5,512,570 itself, generic launch risk is unrestricted because the patent is expired. Commercial scenarios depend on other patents and FDA requirements.

Scenario	Effect of US 5,512,570
Oral generic aprepitant	No blocking effect
Generic injectable fosaprepitant	No blocking effect
Alternative aprepitant injectable formulation	No blocking effect
New NK1 antagonist	No blocking effect unless later patents are implicated
ANDA Paragraph IV challenge	Patent cannot independently support a stay
505(b)(2) product	Patent does not independently prevent approval

A launch may still be delayed by later listed patents, exclusivity, formulation differences, clinical requirements, or manufacturing constraints.

Key Takeaways

US Patent 5,512,570 is an early Merck-related patent covering methods of treating or preventing emesis with broad morpholine-based NK1-antagonist structures.
Claim 1 is a large Markush method claim covering extensive substituent, heterocycle, linker, phosphate, sulfonate, succinate, and prodrug alternatives.
Claims 12-15 narrow the estate to specified compounds and N-methyl-D-glucamine salts.
The patent is historically relevant to aprepitant and fosaprepitant chemistry, but it is not the only or principal patent protecting those products.
The patent expired in approximately November 2013.
It has no current Orange Book blocking effect and cannot independently support a present Paragraph IV stay.
Current freedom-to-operate analysis must focus on later patents covering specific products, formulations, methods of use, and manufacturing processes.

FAQs

Does US 5,512,570 cover injectable fosaprepitant?

Its phosphate and salt claim language is consistent with injectable prodrug embodiments associated with fosaprepitant, but the patent is expired and no longer blocks commercialization.

Can a generic manufacturer rely on US 5,512,570 for an aprepitant launch?

A generic manufacturer benefits from the patent’s expiration, but launch timing depends on later patents, FDA requirements, and product-specific Orange Book certifications.

Is US 5,512,570 a composition-of-matter patent?

No. The supplied claims are principally method claims requiring administration of defined compounds for treatment or prevention of emesis.

Did the patent protect the N-methyl-D-glucamine salt?

Claims 13 and 15 expressly identify N-methyl-D-glucamine salt embodiments. Those claims are expired with the patent.

Does expiration remove all patent risk for aprepitant products?

No. It removes the risk from this patent. Later patents may have covered the active ingredient, formulations, methods of use, injectable products, or manufacturing processes.

References

United States Patent and Trademark Office. (1996). U.S. Patent No. 5,512,570: Morpholine compounds useful as neurokinin antagonists.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations.
U.S. Food and Drug Administration. (2003). Emend (aprepitant) prescribing information.
U.S. Food and Drug Administration. (2008). Emend for Injection (fosaprepitant dimeglumine) prescribing information.
U.S. Congress. (1984). Drug Price Competition and Patent Term Restoration Act of 1984, 21 U.S.C. § 355 and 35 U.S.C. §§ 156, 271.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
European Patent Office	0748320	⤷ Start Trial	08C0019	France	⤷ Start Trial
European Patent Office	0748320	⤷ Start Trial	SPC/GB08/021	United Kingdom	⤷ Start Trial
Austria	227722	⤷ Start Trial
Australia	1975095	⤷ Start Trial
Australia	700611	⤷ Start Trial
Bulgaria	100798	⤷ Start Trial
Bulgaria	62811	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,512,570

Summary for Patent: 5,512,570