US Patent 4,452,808: Scope, Claim Map, and US Patent Landscape for D2-Receptor Indolone Agonists
US 4,452,808 claims a defined indolone scaffold and a narrow set of substitutions, with patentable embodiments tied to specific D2-receptor agonist compounds and fixed composition formats (dosage unit mg range, antihypertensive use). The claim set is structured as (1) compound formula coverage, (2) species claims to identified exemplars (notably “4-(2-di-n-propylaminoethyl)-2(3H)-indolone” and salts), and (3) composition claims that require D2-agonist activity plus pharmaceutical carrier and dosage-unit constraints.
What is the patent’s claimed chemical scope (compound formula claims)?
Core claim language
Independent claim 1 covers:
- “A compound of the structural formula: ##STR4##”
- with variable definitions:
- R is limited to specific amino substituent types:
- amino
- C1-6 lower alkylamino
- di-(C1-6 lower alkyl)amino
- allylamino
- diallylamino
- N-(C1-6 lower alkyl)-N-allylamino
- benzylamino
- dibenzylamino
- phenethylamino
- diphenethylamino
- 4-hydroxyphenethylamino
- di-(4-hydroxyphenethyl)amino
- R1, R2, R3 are each hydrogen or C1-4 lower alkyl
- and includes pharmaceutically acceptable acid addition salts.
Scope implications from the variable set
Even without reproducing the missing structural depiction (##STR4##), claim 1 constrains scope through three levers:
- Substitution identity at “R”: only certain amine patterns are allowed. This is not a broad “any amine” claim; it is a whitelist.
- Substitution identity at R1/R2/R3: each can be H or C1-4 alkyl only, limiting electronic/steric diversity.
- Salt form: acid addition salts are included, expanding practical claim coverage to multiple salt variants for the same free base.
How narrow are the asserted species (claims 2–7)?
Claims 2–7 carve out specific embodiments within the claim 1 genus. These are the key enforceability anchors because they map to concrete named structures and salts.
Species coverage
- Claim 3: “4-(2-di-n-propylaminoethyl)-2(3H)-indolone” (free base or salt by definition in the claim)
- Claim 4: same compound as the free base
- Claim 5: same compound as hydrochloride
- Claim 2: limits R1, R2, R3 to H, sets n = 2, and specifies R ∈ {amino, di-n-propylamino, n-propyl-n-butylamino, 4-hydroxyphenethylamino}
- Claim 6: “4-(2-aminoethyl)-2(3H)-indolone” (and salts)
- Claim 7: “4-(4-hydroxyphenethylaminoethyl-2(3H)-indolone” (and salts)
Practical effect
- Claims 4 and 5 create tight claims to specific forms (free base vs HCl salt), which matters because many development programs screen for different salts. The presence of both forms reduces “design-around” leverage based only on switching free base vs salt (at least for HCl).
- Claim 6 and 7 expand beyond the di-n-propyl variant to other amine substitutions that still fall in the claim 1 whitelist.
What does claim 8 add: use-limitation via D2 receptor agonist activity?
Independent composition claim 8
Claim 8 covers a pharmaceutical composition having D2 receptor agonist activity, comprising:
- “a nontoxic, agonist quantity of a compound of the structural formula: ##STR5##”
- with the same R and R1/R2/R3 definitions as in claim 1
- in dosage unit form
- combined with a pharmaceutical carrier.
Scope implication of “D2 receptor agonist activity”
The claim is not merely a composition; it is a composition with a pharmacological functional requirement:
- The formulation must contain an active quantity of a covered compound that exhibits D2 agonist activity.
From an enforcement standpoint, this increases the number of pathways for invalidity challenges to depend on whether prior art compounds or formulations already demonstrated D2 agonist activity, even if the structural scope overlaps.
How do composition dependent claims narrow the use and dosage?
Claims 9–10: compound specificity inside compositions
- Claim 9: composition where the D2-agonist compound is 4-(2-di-n-propylaminoethyl)-2(3H)-indolone (or salt)
- Claim 10: composition where the compound is hydrochloride
Claim 11: therapeutic use limitation
- Claim 11: composition in dosage unit form adapted for use as an antihypertensive composition.
This adds a downstream use constraint. It can be helpful for enforcement where D2 agonist activity could be argued for the compound generally, but the composition is marketed or used specifically for hypertension.
Claim 12: dosage unit mg range
- Claim 12: quantity per dosage unit is 50–500 mg base weight of the compound.
This is a hard numerical boundary. If a product lands outside the range (for example, 10 mg or 1 g per unit), claim coverage may be harder to assert.
What is the practical “claim map” from molecule to product?
Compound set explicitly claimed (species)
Key molecules named in dependent claims:
- 4-(2-di-n-propylaminoethyl)-2(3H)-indolone
- 4-(2-di-n-propylaminoethyl)-2(3H)-indolone hydrochloride
- 4-(2-aminoethyl)-2(3H)-indolone
- 4-(4-hydroxyphenethylaminoethyl-2(3H)-indolone
Product claim pathways
- If a company sells the free base or HCl salt: claims 4–5 and composition claims 9–10 matter most.
- If a company sells another acid salt: claim 1 and claim 8 include “acid addition salts,” but the “hydrochloride” specific claims (5 and 10) only bind the HCl salt.
- If a company targets hypertension specifically: claim 11 creates use tethering.
- If a company’s dosage differs from 50–500 mg base weight per unit: claim 12 narrows coverage.
What is the US patent landscape around US 4,452,808 (scope-based inference only from the claim set provided)?
You provided only the claims text for US 4,452,808. Without bibliographic data (application number, filing date, priority, publication/issuance status of related family members, and examiner-cited references), a complete landscape cannot be produced without risking incorrect assertions about:
- which prior art patents were cited,
- whether there are direct overlap patents on the indolone scaffold or D2 agonists,
- whether intervening publications affect novelty or obviousness,
- or whether other US patents in the same chemical space have earlier effective dates.
Per operating constraints, this response does not supply unverified landscape claims.
What can be stated strictly from the claim structure is how the patent would typically sit in a landscape:
- Chemical genus coverage (claim 1) targets a defined indolone substitution pattern with a whitelist of R amines and limited R1/R2/R3 alkyl choices.
- Species and salt claims (claims 3–7) create enforceable anchors around specific D2 agonist exemplars.
- Composition claims (claims 8–12) add formulation constraints and a hypertension use limitation plus a fixed mg-per-unit range.
This structure is designed to capture both:
- direct infringement by making/selling the claimed compound (claims 1, 3–7),
- and indirect infringement via drug product formats (claims 8–12), particularly for a hypertension indication and within the stated dosing units.
Design-around sensitivity: where competitors can break coverage (based on claim text only)
1) Substitution changes outside the R whitelist
Claim 1 limits R to specific amino substituent categories and named substituents (e.g., amino, C1-6 alkylamino, di-(C1-6 alkyl)amino, allyl/diallyl, benzyl/dibenzyl, phenethyl/diphenethyl, 4-hydroxyphenethylamino, di-(4-hydroxyphenethyl)amino). Compounds using other amine classes or different linker chemistries would not meet R as defined.
2) R1/R2/R3 outside “H or C1-4 lower alkyl”
If R1/R2/R3 introduce groups outside hydrogen or C1-4 alkyl, the compound claim may fall outside scope.
3) Avoidance of hydrochloride
Claims 4 and 5 are explicit for free base and hydrochloride respectively. Switching salt form may avoid those specific claims, though claim 1 and claim 8 still include “acid addition salts” generally.
4) Product dosage units outside 50–500 mg base weight
Even if the same compound is used, claim 12 requires the dosage unit amount within 50–500 mg base weight. Outside that window, claim 12 likely fails, though other composition elements (claims 8–11) could still remain.
5) Indication positioning
Claim 11 ties composition “adapted for use” as an antihypertensive. Product labeling and clinical regimen matter for this limitation.
Key takeaways
- US 4,452,808 is built around a defined indolone chemical genus (claim 1) constrained by a whitelist of R amine substituents and limited R1/R2/R3 substitution options (H or C1-4 alkyl).
- The enforceability of the patent is strengthened by species claims to named compounds and specific salt/free-base forms, especially 4-(2-di-n-propylaminoethyl)-2(3H)-indolone and its hydrochloride (claims 3–5).
- Product-level coverage is provided via pharmaceutical composition claims that require D2 receptor agonist activity plus standard carrier and dosage unit format (claim 8), then narrowed to specific compounds (claims 9–10), an antihypertensive adaptation (claim 11), and a fixed dosage unit mg range (claim 12).
- A credible landscape requires filing and priority data and the cited prior art for accurate mapping; the claim text alone supports only structural and functional scope analysis, not a validated US patent overlap chart.
FAQs
1) Which compound is most explicitly covered in both compound and composition claims?
4-(2-di-n-propylaminoethyl)-2(3H)-indolone and its hydrochloride, via claims 3–5 (compound) and claims 9–10 (composition).
2) Does the patent protect only the free base or also salts?
It includes pharmaceutically acceptable acid addition salts in claim 1 and claim 8, and it also includes the specific hydrochloride in claims 5 and 10.
3) What additional constraints do composition claims impose beyond compound claims?
Claim 8 requires a dosage unit form, a pharmaceutical carrier, and D2 receptor agonist activity, then dependent claims add antihypertensive adaptation (claim 11) and a 50–500 mg base weight per dosage unit constraint (claim 12).
4) Where is the most obvious “numerical” vulnerability for competitors?
The dosage unit quantity: 50–500 mg base weight per unit (claim 12).
5) Can a different salt avoid coverage?
It may avoid the hydrochloride-specific claims (5 and 10), but general salt coverage remains in acid addition salt language within claim 1 and claim 8.
References
[1] United States Patent 4,452,808 (claims as provided by user).
