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Patent landscape, scope, and claims: |
US Patent 5,142,051: Scope, Claims, and US Landscape
What does US 5,142,051 claim, in scope terms?
US Patent 5,142,051 claims a class of nucleobase-linked compounds defined by a single general chemical formula (shown as “##STR3##” in the claim text) with a substituent variable B. The claims are structured as:
- Claim 1 (independent): broadest definition, covering multiple nucleobase moieties selected from a defined list of B groups.
- Claim 2: narrows Claim 1 to a smaller subset of B moieties (pyrimidines and 5-substituted uracil).
- Claim 3: narrows further to a single embodiment where B = cytosin-1-yl.
Claim 1: full list of B groups (broadest scope)
Claim 1 covers compounds where B is one of:
- uracil-1-yl
- cytosin-1-yl
- 5-methylcytosin-1-yl
- thymin-1-yl
- 5-fluoruracil-1-yl
- guanin-9-yl
- guanin-7-yl
- adenin-3-yl
- hypoxanthin-9-yl
- 2-methyladenin-9-yl
- 2-methylthioadenin-9-yl
- 2-aminoadenin-9-yl
- 2-aminopurin-9-yl
- N6-dimethyladenin-9-yl
- 8-bromoadenin-9-yl
- 8-hydroxyadenin-9-yl
- 6-hydroxylaminopurin-9-yl
- 6-hydrazinopurin-9-yl
- 6-thiopurin-9-yl
- purin-9-yl
- xanthin-9-yl
Scope implication: This is not limited to nucleosides or nucleotides. It is a template claim anchored on a fixed core structure (the unspecified “##STR3##”), with B spanning both pyrimidines and purines/xanthines, including ring-substituted variants (fluoro, methyl, bromo, hydroxy, amino, thio, hydrazino, hydroxylamino, N6-dimethyl).
Claim 2: narrowed B set
Claim 2 limits Claim 1 to:
- uracil-1-yl
- cytosin-1-yl
- 5-methylcytosin-1-yl
- thymin-1-yl
- 5-fluorouracil-1-yl
Scope implication: Claim 2 is a pyrimidine-only subset, retaining the 5-substituted uracil/cytosine variants. It removes all purines, hypoxanthine, xanthine, and adenine variants, plus the 7- and 9-position guanin variants.
Claim 3: single-embodiment B
Claim 3 limits Claim 2 to:
Scope implication: Claim 3 is the “single-point” fallback with the most specific nucleobase selection.
How broad is the patent across nucleobase space?
The claim strategy covers a wide nucleobase design space but only through the enumerated B list. The list includes:
Enumerated nucleobases and substitution patterns
| Category |
B options included in Claim 1 |
Count (from provided claim text) |
| Pyrimidines |
uracil-1-yl, cytosin-1-yl, 5-methylcytosin-1-yl, thymin-1-yl, 5-fluoruracil-1-yl |
5 |
| Purines |
guanin-9-yl, guanin-7-yl, adenin-3-yl, 2-methyladenin-9-yl, 2-methylthioadenin-9-yl, 2-aminoadenin-9-yl, 2-aminopurin-9-yl, N6-dimethyladenin-9-yl, 8-bromoadenin-9-yl, 8-hydroxyadenin-9-yl, 6-hydroxylaminopurin-9-yl, 6-hydrazinopurin-9-yl, 6-thiopurin-9-yl, purin-9-yl |
14 |
| Xanthines |
xanthin-9-yl, hypoxanthin-9-yl |
2 |
Total B options in Claim 1 as written: 21.
Design takeaway: A competitor who substitutes a nucleobase not in the enumerated B list is likely outside the literal scope of Claim 1, unless an issued dependent claim or doctrine-of-equivalents theory is asserted. Conversely, if the competitor uses one of the enumerated B groups and matches the rest of the fixed formula, the risk concentrates on formula core identity, not on nucleobase novelty.
What does the claim architecture mean for infringement risk?
Literal infringement hinges on two elements
- The compound must match the general formula (##STR3##).
- The variable B must be one of the enumerated nucleobase moieties.
Because the claims are Markush-style via “wherein B is selected from the group consisting of…,” the enumerated list is a hard boundary for literal scope.
Claim dependency creates layered coverage
- Claim 1: highest risk across broad nucleobase variants (pyrimidines + many purine/xanthine variants).
- Claim 2: narrower but still covers common pyrimidine analogs (uracil, cytosine, thymine, and 5-substituted uracil/cytosine).
- Claim 3: highest specificity; useful for establishing infringement on a single known product class.
What is the practical claim “landscape” across the claim set?
With only three claims provided, the patent landscape is constrained to a single structural template and three progressively narrow B selections. That yields a simple “grid” of possible designs:
Coverage matrix
| Candidate compound matches fixed core formula? |
B is among Claim 1 list? |
B is among Claim 2 list? |
B = cytosin-1-yl? |
Claim risk tier |
| No |
any |
any |
any |
Lower (no literal fit to the formula) |
| Yes |
Yes |
Yes/No |
Yes/No |
Claim 1 risk if B in list |
| Yes |
No |
Yes |
Yes/No |
Claim 2 only if B in Claim 2 list, else none |
| Yes |
No |
No |
Yes |
Only if B actually equals cytosin-1-yl and B fits enumerated lists; otherwise none |
The matrix collapses in practice to a single question: is B in the relevant enumerated set and does the core match “##STR3##”?
What should a US freedom-to-operate review focus on for this patent?
The provided claim text omits the explicit structural formula details behind “##STR3##.” A US landscape review should therefore operationalize infringement analysis as follows:
Technical checks (claim 1 first, then fallbacks)
- Fixed core identity
Compare the competitor’s compound scaffold directly to the “##STR3##” structural definition (substitution positions, linker, valence, and ring attachment method).
- B assignment (nucleobase moiety + attachment position)
Verify both the nucleobase type and the attachment position implied by naming (e.g., “uracil-1-yl” vs “cytosin-1-yl” vs “adenin-3-yl” vs “purin-9-yl”).
- Enumerated substitution status
Confirm whether variants like fluoro, bromo, hydroxy, N6-dimethyl, 6-hydrazinyl, 6-thiopurinyl, or methylthio are present in the exact form listed.
Design-around leverage
- Best-case avoidance (for literal): use a B moiety not enumerated in the relevant claim scope (not in Claim 1 if aiming to avoid any claim, not in Claim 2 if designing to avoid the pyrimidine subset).
- Second-best avoidance: keep B enumerated but alter the core so it no longer matches the fixed structural formula in “##STR3##.”
What is the patent landscape in the US for compounds like this?
The provided data includes claim text only, with no bibliographic fields (assignee, filing date, expiration/term adjustments, related family members), and no cited references, thus a complete US landscape cannot be built from the information given.
What can be said from claim content alone
- The patent scope is nucleobase-position selective and enumerated, suggesting it targets a specific attachment geometry between a fixed scaffold and nucleobase analogs.
- The breadth across purine substitutions implies it covers at least one medicinal chemistry “series” rather than a single compound.
What cannot be asserted from the provided data
- Which specific commercial products or research compounds are practicing the claim.
- Which earlier patents or later patents in the US cite, compete, or dominate this space.
- Whether US 5,142,051 has common priority to other jurisdictions, continuations, or corresponding European/WO families.
- Expiration date, terminal disclaimers, reexamination outcomes, or whether prosecution history narrows the Markush interpretation.
Given the constraints, the only defensible “landscape” conclusion is that the patent’s enforceable reach, as provided, is confined to the enumerated B groups mapped onto the fixed “##STR3##” core.
Key takeaways
- US 5,142,051 claim scope is a fixed chemical template (“##STR3##”) with a Markush variable B covering 21 enumerated nucleobase moieties in Claim 1.
- Claim 2 narrows to 5 pyrimidine/5-substituted uracil-cytosine-type B options.
- Claim 3 isolates cytosin-1-yl.
- Infringement risk concentrates on whether a competitor’s compound matches the fixed core and uses one of the enumerated B moieties (attachment position included).
- A complete US patent landscape (other US patents, citations, family members, and remaining validity risk) cannot be derived from the provided claim text.
FAQs
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Is the scope limited to pyrimidines?
No. Claim 1 includes both pyrimidines and many purine/xanthine variants; Claim 2 is the pyrimidine-only subset.
-
How does the Markush “B is selected from the group consisting of” affect coverage?
Literal scope depends on B being one of the listed nucleobase moieties; unlisted nucleobases are outside literal coverage.
-
Does Claim 3 expand coverage beyond Claims 1 and 2?
No. Claim 3 is narrower: it restricts B to cytosin-1-yl.
-
What is the main technical lever for design-around?
Either change the fixed core away from “##STR3##” or select a B moiety not enumerated in the applicable claim.
-
Can this claim be mapped to a specific marketed drug from the provided information?
Not from the claim excerpt alone; the key structural definition is missing behind “##STR3##,” and no bibliographic/compound identification is provided.
References
[1] United States Patent 5,142,051. Claims 1-3 (as provided in user input).
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