United States Patent 4,724,233: Scope, Claims, and US Patent Landscape for Phosphonylmethoxyalkyladenine Antivirals
What is US 4,724,233 claiming in plain terms?
US Patent 4,724,233 claims a method of treating viral diseases in a patient by administering an effective antiviral amount of a specific chemical class: phosphonylmethoxyalkyladenine derivatives of formula (I), with defined substituent options for R1 and R2, defined stereochemistry when R1 is not methylene, and defined salt/free-acid forms.
The independent claim (claim 1) is drafted as a broad medical use claim with chemical limitations (formula (I) plus stereochemistry plus salt/free acid) and therapeutic limitation (“virus diseases” generally, later narrowed by examples to multiple virus families in dependent claims).
Claim 1: Key structural and legal scope elements
Claim 1 has five scope gates:
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Therapeutic action
- “method for treating virus diseases”
- “administering … an effective antiviral amount”
-
Drug class: phosphonylmethoxyalkyladenine (formula I)
- The claim covers adenine derivatives bearing a phosphonylmethoxyalkyl side chain, where the structure is defined by R1 and R2.
-
R1 options (side-chain linker/geometry)
- R1 is one of:
- methylene, or
- --CH(OH)--CH2 --, or
- a cyclic ester-capable linkage given by the additional R1 fragment (as shown in the claim text).
-
R2 options and optional cyclization
- R2 is “a hydroxyl group.”
- When R1 is different from methylene, “R1 and R2 may be linked with each other to form a cyclic ester group.”
-
Stereochemistry and salt/free-acid constraints
- “adenine derivative being in (RS) or (S) form when R1 is different from methylene”
- “free acid or a salt thereof”
- salts selected from:
- alkali metal
- ammonia
- amine salts
Claims 2 to 12: narrowing examples with explicit viruses
Practical scope boundary
The claim does not cover:
- unrelated nucleoside analogs without the specific phosphonylmethoxyalkyladenine core and defined R1/R2 logic
- ester/prodrug variants unless they still fall within the formula (I) definitions for R1/R2 (including cyclic ester possibility)
- salts outside “alkali metal, ammonia, and amine salts”
- stereoisomers outside “(RS) or (S)” when R1 is not methylene
It does cover:
- any viral disease where the accused therapy uses one of the defined formula (I) compounds in the specified stereochemical/salt form at an “effective antiviral amount,” and where the virus disease is one of the listed viruses if a dependent claim is asserted.
What is the claim-by-claim infringement relevance (how it hits competitors)?
Claim 1 (broadest): method of treating “virus diseases”
Claim 1 is the anchor. A competitor’s product would need to match all of the following to fall within Claim 1:
-
Drug identity must fit formula (I)
The competitor’s active ingredient must be a phosphonylmethoxyalkyladenine with the R1 and R2 constraints. This is the primary novelty hook.
-
Stereochemistry alignment (when R1 is not methylene)
- If the molecule corresponds to “R1 different from methylene,” the claim limits to (RS) or (S).
-
Salt/free acid form
- Must be the free acid or one of the claimed salts.
-
Route and dosage form
- The claim is method-based but does not expressly limit route, dosing schedule, or dosage form in the excerpt provided. The “administering” element typically captures oral, parenteral, or other routes depending on how the compound is formulated and used.
-
Use in viral disease treatment context
- “treating virus diseases” is broad; in US litigation this is often supported by labels, prescribing information, clinical protocols, or physician intent evidence.
Infringement strategy effect: Claim 1 is likely asserted against any company using or marketing a close analog that still meets formula (I), even if the marketing focuses on one virus.
Claim 2: specific compound lock
Claim 2 is both narrower and higher-confidence for enforcement:
- If an accused product’s active is (S)-9-(3-hydroxy-2-phosphonylmethoxypropyl)adenine, it directly maps.
Infringement strategy effect: Claim 2 reduces interpretive fights about R1/R2/cyclic ester language because the compound is explicitly named.
Claims 3 to 12: virus-specific use
These dependent claims create separate claim handles by virus class.
How they matter in practice
- If a competitor’s clinical program targets, say, herpes virus, then Claim 3 becomes the immediate claim to plead.
- If a competitor’s product is positioned for vaccinia, Claim 11 is the immediate hook.
Important limitation
- These are dependent on Claim 1, so the competitor must still meet formula (I) identity (and stereochemistry/salt constraints) in addition to virus context.
How broad is “formula (I)” legally?
Without the full drawn formula (I) and its exact substituent mapping text, the enforceable breadth hinges on the claim’s enumerated structural degrees of freedom:
-
R1 is limited to three structural categories:
- methylene
- hydroxy-methylene substituted chain (“--CH(OH)--CH2 --”)
- another R1 fragment that permits cyclic ester formation when R1 links with R2
-
R2 is limited to hydroxyl, with conditional cyclization when R1 is not methylene.
-
Cyclic ester inclusion is explicit:
- If R1 differs from methylene, R1 and R2 can form a cyclic ester group. That means some intramolecular ester variants remain inside the claim.
-
Salt set is explicit:
- alkali metal, ammonia, and amine salts only.
- Other salts (e.g., certain organic acids) are outside unless a court construes them as “amine salts” (which is fact-and-chemistry dependent).
This makes the claim both:
- substantive (limited by exact chemical architecture and salt identity), but
- broad in treatment scope (any “virus diseases,” then enumerated viruses in dependent claims).
What is the likely US patent landscape structure around this patent?
US antiviral nucleoside analog landscapes around this era typically show:
- Core chemical claims by the originator (multiple filings: base structure + salts + stereoisomers + prodrugs/cyclic forms).
- Medical use claims (specific virus indications).
- Follow-on patenting (formulation, dosing regimens, combinations, and additional salts/prodrugs).
For US 4,724,233 specifically, the excerpted claims show that this patent is a medical-use umbrella tethered to a chemical scaffold, not a formulation claim.
Where it sits in the landscape
Given:
- chemical definition via formula (I)
- multiple dependent virus indications
- explicit stereochemical compound in claim 2
the patent functions as a bridge between:
- chemical patent coverage on phosphonylmethoxyalkyladenine derivatives, and
- indication-driven exclusivity in US enforcement.
Common landscape pressure points (what competitors will design around)
Competitors trying to avoid Claim 1 generally target one of the claim gates:
- Chemical gate: alter the backbone so it no longer fits the “phosphonylmethoxyalkyladenine” formula (I) definition
- Stereochemistry gate: supply a stereochemical isomer set outside “(RS) or (S)” when R1 is not methylene
- Salt gate: use salts outside the enumerated categories
- Virus use gate: position development outside dependent virus claims while still risking the general Claim 1 (unless Claim 1 is later constrained during litigation to specific viruses via construction or prosecution history estoppel)
Because Claim 1 is not limited to a particular virus in the excerpt, the “virus gate” is more about strengthening dependent claim assertions than about avoiding the whole patent.
What does the claim set imply about inventorship coverage and enforcement priority?
Two claim classes create different enforcement leverage:
1) Scaffold coverage (Claim 1)
- Used to allege broad method infringement if the active ingredient matches formula (I).
2) Indication coverage (Claims 3 to 12)
- Used to add specificity for pleading, settlement leverage, and jury clarity, particularly if the accused product’s clinical narrative matches one of the listed viruses.
3) Compound lock (Claim 2)
- Often used as the primary “clean mapping” claim when the accused molecule is identical.
Risk map for investors and R&D teams
Highest risk: products matching Claim 2’s explicit stereochemical compound
- Active ingredient identity match is the hardest to dispute.
- Virus indication is secondary but increases enforcement probability.
Medium risk: formula (I)-conforming derivatives with alternate salts
- If the molecule is inside formula (I) but formulated as a non-claimed salt, defenses can focus on salt category and claim construction.
- Litigation will often turn into technical chemistry claim mapping.
Lower risk: molecules that break the phosphonylmethoxyalkyladenine architecture
- If R1/R2 or the phosphonylmethoxy linkage pattern is altered so formula (I) is not met, the patent becomes much harder to assert under Claim 1.
Key Takeaways
- US 4,724,233 is a method-of-treatment patent for viral diseases anchored to phosphonylmethoxyalkyladenine derivatives defined by formula (I).
- Claim 1 is broad on disease (“virus diseases”) but tight on chemical identity: specific R1/R2 rules, stereochemistry (RS/S when R1 is not methylene), and allowed salt categories.
- Claim 2 is the enforceable “lock” on (S)-9-(3-hydroxy-2-phosphonylmethoxypropyl)adenine.
- Claims 3-12 provide dependent coverage for multiple virus families, enabling indication-targeted enforcement while still requiring satisfaction of Claim 1’s chemical constraints.
- In a competitive landscape, design-arounds most plausibly attack: formula (I) structure, allowed stereochemical set, or salt category.
FAQs
1) Does Claim 1 cover any antiviral use or only viral diseases?
Only viral diseases. The claim language requires “treating virus diseases” and administering an effective antiviral amount of the formula (I) compound.
2) Is the patent limited to a single compound?
No. Claim 1 covers a class of phosphonylmethoxyalkyladenine derivatives by formula (I). Claim 2 adds an explicit specific compound within that class.
3) Are salts limited in the claims?
Yes. Claim 1 limits salts to alkali metal, ammonia, and amine salts, plus the free acid.
4) Do the dependent claims change the required chemical identity?
No. Claims 3-12 are dependent on Claim 1, so they still require the same formula (I) chemical identity, stereochemistry, and salt/free acid status.
5) Which claim is likely the easiest to assert?
Usually Claim 2 if an accused product uses the same stereochemical compound named in the claim. If not, Claim 1 becomes the main target, with the virus-specific dependent claims used depending on indication.
References
[1] U.S. Patent No. 4,724,233, “Method for treating virus diseases” (claims provided in prompt).
