United States Patent RE44638 Scope and Claims Analysis for (S)-5-fluoro-3-phenyl-2-[1-(9H-purin-6-ylamino)-propyl]-3H-quinazolin-4-one
Executive summary: RE44638 (US reissue) claims a single compound of formula (S)-5-fluoro-3-phenyl-2-[1-(9H-purin-6-ylamino)-propyl]-3H-quinazolin-4-one and a second claim to a pharmaceutical composition containing that compound plus excipients. The claim scope is narrow at the US level because it is defined by a specific stereochemical configuration (S), a specific quinazolinone core substitution pattern, and the specific pendant purin-6-ylamino-propyl side chain. The legal and commercial exposure is driven primarily by (i) whether any competitor markets the same active or a salt form, (ii) whether competitors use different stereochemistry or substitute different purine-linkage topology, and (iii) whether challengers can attack the reissue basis, written description/enablement, or definiteness, rather than by broad process or formulation claim coverage.
What is the exact compound covered by RE44638 and how narrow is the (S) stereochemistry?
Featured snippet answer: Claim 1 covers the specific stereoisomer (S)-5-fluoro-3-phenyl-2-[1-(9H-purin-6-ylamino)-propyl]-3H-quinazolin-4-one and pharmaceutically acceptable salts.
Claim 1 structure and “how to design around” triggers
Claim 1 is a classic “compound-of-formula” claim with a tightly constrained identity. Design-around risk concentrates on three “locks”:
- Stereochemistry lock: the claim requires (S) at the chiral center incorporated in the “2-[1-(…)-propyl]” substituent framework. An (R) analog is outside the literal claim if the formula is stereospecific and not written generically as “enantiomers.”
- Core scaffold lock: the bicyclic/heterocycle core is specifically 3H-quinazolin-4-one, with the substitution pattern:
- 5-fluoro
- 3-phenyl
- 2-[(1-(9H-purin-6-ylamino)-propyl)]
- Purin attachment lock: the side chain is attached via “9H-purin-6-ylamino”. That linkage position (purin-6-ylamino) is typically the key differentiator versus purin-7-ylamino or other nucleobase linkages.
Salt coverage and practical implications
Claim 1 expressly includes “pharmaceutically acceptable salt thereof.” Salt form design-arounds are therefore less protective if the salt is “pharmaceutically acceptable” and the underlying free base remains the same stereochemical entity. Competitors typically instead change the free base identity or stereochemistry.
What formulation and dosage forms are covered by RE44638 claim 2?
Featured snippet answer: Claim 2 covers any pharmaceutical composition comprising the claim 1 compound and at least one pharmaceutically acceptable excipient, without limiting dosage form, route, or release profile.
Claim 2 scope: broad on dosage form, narrow on actives
Claim 2 is broad only in the excipient dimension. It is narrow because it still requires the exact compound of claim 1. It does not, based on the provided text, add limitations such as:
- tablet vs capsule vs injectable
- controlled release or specific polymer systems
- pH ranges
- particle size
- specific manufacturing conditions
As written, claim 2 can read on most conventional solid and liquid dosage forms that include the compound.
How do RE44638 claim elements map to a competitive molecule-by-molecule infringement test?
Featured snippet answer: Infringement risk turns on whether a product’s active ingredient is the same (S) enantiomer with the same quinazolinone substitution pattern and purin-6-ylamino-propyl side chain (and uses a pharmaceutically acceptable salt of that same active).
Literal infringement hot spots
A competitor’s active ingredient would fall within claim 1 if all are true:
- stereochemistry matches (S)
- quinazolinone core matches 5-fluoro-3-phenyl-3H-quinazolin-4-one
- side chain matches 1-(9H-purin-6-ylamino)-propyl at the 2-position
Common legal/chemical “escape” positions
- Switch enantiomer: (R)-enantiomer market use is the first obvious escape route if stereochemistry is strictly required in the formula.
- Shift nucleobase attachment: purin-7-ylamino or other purine attachment patterns can remove literal match.
- Change linkage chemistry: replacing the amino linkage or using a different heteroatom attachment point may avoid the specific formula.
- Modify core substitution: replacing 5-fluoro or 3-phenyl, or altering the quinazolinone N- and C-positions, breaks literal identity.
What patent landscape risks follow from this claim set for US generic or biosimilar entry?
Featured snippet answer: RE44638 is a compound and composition patent; it is generally aimed at generic entry by covering the active ingredient itself. The most direct risk for generics is making or selling the same active (including salts). For biosimilars, this patent is not a biologic patent claim on its face, so biosimilar pathways are not the primary risk driver.
Generic entry: where claim coverage bites
- ANDA (small molecules): The ANDA applicant must address the risk of infringing claim 1’s specific compound and claim 2’s composition definition if it files for the same drug substance and markets a composition containing it.
- Paragraph IV: Typical challenge strategy for a compound patent is an invalidity/non-infringement theory tied to stereochemistry, structure, or patentability requirements.
- Design-around feasibility: Because the claim is highly structured, design-around via stereochemical switch or purine-attachment changes may be chemically plausible while avoiding literal infringement. The harder question becomes whether such changes still meet the same pharmacology and regulatory endpoints.
Settlement and “launch after” scenarios
Because claim 1 is a single, well-defined structure claim, settlement timelines commonly hinge on:
- whether the paragraph IV filer’s product is an enantiomer different from the claimed (S) form
- whether the settlement covers only commercial product launch or also manufacturing and development activities
- whether any later patents on related analogs extend exclusivity
What are the likely reissue implications for claim scope under US practice (RE patents)?
Featured snippet answer: A US reissue (RE) can broaden, narrow, or correct claims depending on reissue history, but the actionable scope for infringement is the issued RE claim set. Based on the provided claim text, RE44638 reads as a narrow structural claim and a general composition claim.
Why reissue matters in litigation posture
Even when claim text is narrow, reissue can affect:
- priority and intervening rights
- ability to adjust claim scope relative to the originally examined claims
- vulnerability to procedural invalidity arguments (for some RE histories)
- how courts interpret the reissue’s relationship to the earlier base patent and its prosecution record
Those questions are fact-dependent on the original non-reissue patent number, reissue filing date, and the reissue specification and file wrapper, which are not provided in the prompt. The only legally actionable scope from the prompt is the claim language itself.
What patent expiration date exposure exists for RE44638 compound claims?
Executive summary: No expiration date can be computed from the claim text alone. Patent term depends on the underlying non-reissue application filing date, any patent term adjustments, and any terminal disclaimers. The prompt provides neither the priority date nor the underlying patent number.
Which companies are likely affected by RE44638?
Executive summary: No identifiable parties can be listed from the claim text alone. Assignments, Orange Book listings, and litigation dockets require at least the patent bibliographic data (assignee, related patents, and the linked FDA drug) that are not included in the prompt.
How strong is the patent estate for this target compound based on claim coverage alone?
Featured snippet answer: Claim strength is high on literal structure for the exact (S) compound because the claim identity is explicit, but the patent’s strategic breadth is limited by the absence of broader claims (e.g., method-of-use, Markush ranges, or genus claims) in the provided text.
Strength factors
- Definite stereochemical definition reduces ambiguity.
- Specific substitution pattern reduces “do they cover my analog?” uncertainty.
- Composition claim covers standard pharmaceutical formulations that include the protected compound.
Weakness indicators (from what is provided)
- Only two claims are described, and claim 1 is narrowly defined.
- There is no provided evidence of broader genus coverage or method-of-use coverage that would block not only the exact active but also therapeutic strategies or dosing regimens.
What would generic entry risk look like for an ANDA on the same active?
Featured snippet answer: The main ANDA risk is infringement of claim 1 (active ingredient and salts) and claim 2 (any composition containing it). Generic entry is most blocked when the ANDA’s drug substance is the same stereochemical structure and the proposed dosage form includes the same compound.
Likely infringement theories
- Active ingredient equivalence: If the ANDA produces the same compound (S-enantiomer), literal infringement is straightforward.
- Salt marketing: Even if the generic uses a salt, claim 1 covers pharmaceutically acceptable salts unless the salt is non-pharmaceutically acceptable or the free base differs structurally.
- Composition claim: If the dosage form contains the compound and excipients, claim 2 is implicated.
Typical defenses to explore in litigation (structure-based)
- non-infringement by enantiomeric difference or altered substitution
- invalidity based on novelty/obviousness or specification defects, depending on reissue and prosecution history
Those arguments require full patent history and the accused product structure, which are outside the prompt.
Are there any likely formulation patents that RE44638 does not cover?
Featured snippet answer: Yes. Claim 2 in the provided text does not limit to any specific delivery system, dosage form, or manufacturing technique. That means RE44638 may not overlap with later patents that protect specific formulations, salts, polymorphs, or process improvements unless those later patents are owned by the same party and cover different aspects of the same drug.
Key Takeaways
- RE44638 claim 1 is a narrow compound claim for the (S) stereoisomer of 5-fluoro-3-phenyl-2-[1-(9H-purin-6-ylamino)-propyl]-3H-quinazolin-4-one plus pharmaceutically acceptable salts.
- RE44638 claim 2 covers any pharmaceutical composition containing that compound and at least one acceptable excipient, without dosage-form limitations.
- Design-around leverage concentrates on stereochemistry (S vs R), purine attachment position (purin-6-ylamino vs other), and preservation of the exact quinazolinone substitution pattern.
- Generic entry risk is highest for ANDAs using the same (S) active ingredient and salts; the claim set is structural, not method-of-use or formulation-system specific, based on the provided text.
FAQs
1) Does RE44638 cover the (R) enantiomer of the same compound?
Claim 1 is written to the (S) enantiomer. The (R) enantiomer is not included on the face of the provided claim language.
2) If a generic sells a different salt form, is it still within RE44638?
Claim 1 includes “pharmaceutically acceptable salt thereof.” Salt form alone typically does not avoid infringement if the underlying active is the same (S) compound.
3) Are specific dosage forms like tablets or injectables covered by claim 2?
Claim 2 covers a pharmaceutical composition containing the claimed compound and excipients, without limiting dosage form.
4) Is this patent likely to be used against biologic competitors?
The provided claims target a small-molecule compound and compositions; biosimilar entry is not the primary framing implied by the claim language.
5) Can competitors avoid infringement by changing the excipients or manufacturing process?
Changing excipients alone does not avoid claim 2 if the composition still contains the claimed compound. Manufacturing process changes would matter only for process-specific claims, which are not provided here.
References (APA)
- United States Patent RE44638 (Reissue). Claim text provided in prompt.
