United States Patent 4,418,208: Scope, Claims, and U.S. Patent Landscape

What does US 4,418,208 claim cover?

US 4,418,208 claims (i) specific small-molecule structures defined by a Markush framework with constrained substituents, and (ii) pharmaceutical compositions that combine those molecules with a stannous reducing agent. The claim set is narrow in substituent identity and in the allowable range of a single integer parameter (n).

Independent claim scope

Claim 1 (compound class)

Covers “a compound having the formula ##STR6## or a pharmaceutically acceptable, water soluble salt thereof”
Substitution rule:
- “one of R2 and R3 is methyl and the other is bromine”
Integer limit:
- “n is 0, 1 or 2”

Claim 4 (composition with stannous reducing agent)

Covers “a composition comprising a stannous reducing agent and a compound having the formula ##STR8## or a pharmaceutically acceptable, water soluble salt thereof”
Same substitution rule:
- “one of R2 and R3 is methyl and the other is bromine”
Same integer limit:
- “n is 0, 1 or 2”

Claim 6 (composition without the methyl/bromine constraint, broader in n)

Covers “a composition comprising a stannous reducing agent and a compound having the formula ##STR9## or a pharmaceutically acceptable, water soluble salt thereof”
Integer limit:
- “n is 0, 1 or 2”

Dependent claims narrowing n

Claim 2: compound of Claim 1 where n is 0
Claim 5: composition of Claim 4 where n is 0
Claim 7: composition of Claim 6 where n is 0

Specific end-point compounds (species claims)

Claim 8 (explicit compound):
“2,2'-[[2-[(3-bromo-2,4,6-trimethylphenyl)amino]-2-oxoethyl]imino]bisacetic acid.”
Claim 9 (explicit compound):
“2,2'-[[2-[(4-bromo-3-methylphenyl)amino]-2-oxoethyl]imino]bisacetic acid.”

These species claims anchor the Markush class to at least two concrete examples with defined bromine/methyl patterns on the aryl ring.

How narrow is the Markush framework?

The claims use Markush-style constraints that materially limit “design-around” space.

Key narrowing parameters

R2/R3 identity constraint
- Only two substitution identities are allowed in the R2/R3 positions:
  - one is methyl
  - the other is bromine
- The claims do not permit other halogens or alkyl groups at those positions within the independent compound claim.
n is capped to three values
- n ∈ {0, 1, 2}
- Dependent claims fix n = 0, which is likely tied to the particular bisacetic acid structure shown in claims 8 and 9.
Salt limitation
- Coverage extends to “pharmaceutically acceptable, water soluble salts.”
- A defendant could attempt to avoid salt infringement by using non-water-soluble forms, but infringement analysis typically still considers equivalents only if the claim language supports it. Here, the claim language is explicit on water-soluble salts.

Practical claim construction impact

The R2/R3 methyl-bromine pairing makes the class closer to a “set of regioisomeric/positional analogs” than to a broad “any substituted” scaffold.
n ∈ {0,1,2} further restricts allowable variants of the core linking unit represented by the variable integer.

What does “stannous reducing agent” do to the composition scope?

The composition claims add a second infringement axis: the presence of a reducing agent component.

Composition claim requirements

Claim 4/5: composition must include
- a stannous reducing agent and
- a compound matching the methyl/bromine and n constraint.
Claim 6/7: composition must include
- a stannous reducing agent and
- a compound matching the formula with n ∈ {0,1,2}.

Scope implications

The composition claims are not merely “pharmaceutical compositions including the compound.”
They require an additional functional component (stannous reducing agent), which narrows the set of products that would directly infringe.
A competitor formulation that omits stannous reducing agents may avoid these composition claims while still risking infringement of the compound claims (claims 1-3, 8-9).

How do claims 8 and 9 relate to the Markush claims?

Claims 8 and 9 are explicit chemical species that fall within the broader formula definitions.

Claim 8 species

“2,2'-[[2-[(3-bromo-2,4,6-trimethylphenyl)amino]-2-oxoethyl]imino]bisacetic acid.”

This species is consistent with the idea that:

the aryl portion contains bromine and methyl substituents aligned to the R2/R3 constraint, and
n likely corresponds to 0 (given dependent claim structure and the explicit bisacetic acid naming that usually maps to a defined n value).

Claim 9 species

“2,2'-[[2-[(4-bromo-3-methylphenyl)amino]-2-oxoethyl]imino]bisacetic acid.”

This species similarly aligns with:

bromine/methyl substitution patterns within the constrained positions, and
a specific n value that is consistent with the “n = 0” dependent claim designations.

Why the relationship matters

If you are assessing infringement risk for a candidate molecule, the species claims provide a direct “hit list” that does not require mapping all Markush elements if the exact compounds are made, used, sold, or imported.

What is the effective infringement boundary?

In enforcement terms, the claims create two boundary types.

Boundary type A: molecular identity

To infringe claim 1/3, an accused compound must satisfy:

the core formula (as shown in ##STR6## or ##STR8##),
the R2/R3 constraint: methyl and bromine in those roles,
n ∈ {0,1,2},
and optionally be a covered water-soluble salt.

To infringe species claim 8 or 9, the accused product must be the exact listed compound (or its covered salt, to the extent salts are encompassed by the operative claim language).

Boundary type B: formulation identity

To infringe claim 4/5/6/7, the accused product must include:

a stannous reducing agent, plus
a compound meeting the relevant formula and n constraints.

This boundary is usually easier to test analytically:

composition testing can detect stannous species and match formulation composition.
molecular analysis can confirm whether the active compound is within the Markush definition or matches claims 8/9.

How to read the claim set for design-around strategy (U.S.)

Because the independent compound claim is structurally constrained, design-around options exist, but they are limited by the claims’ tight substitution and n ranges.

Most direct non-infringing routes

Change the R2/R3 identity rule
- Use substitutes other than “one methyl and the other bromine” in those positions.
- Even swapping to a different halogen would typically miss the literal R2/R3 requirement.
Change n outside 0,1,2
- Using an n value not in the permitted set avoids the literal n constraint.
Avoid water-soluble salts
- If the compound exists only as non-water-soluble forms, you reduce the probability of meeting “water soluble salt” language.
- This is less reliable for enforcement if the product is marketed in a form that meets solubility requirements, but it is a direct textual hook.

Composition-specific avoidance

Keep the compound outside claims 1/3 while also formulating without stannous reducing agent to reduce exposure to claims 4/6.

Where exposure can remain

If a competitor uses the exact species in claims 8 or 9, design-around is harder because the species claims are exact-language claims anchored to named structures.

What does the patent landscape look like around US 4,418,208?

You can map the landscape in three layers: (1) immediate patent family structure, (2) later continuation/incremental amendments, and (3) overlapping chemical space by substitution pattern and n values.

1) Immediate family and U.S. enforceability

US 4,418,208 is a U.S. drug patent with a defined compound class and composition claims featuring a stannous reducing agent. Without additional bibliographic metadata (application number, filing date, and continuation history), the enforceability window and any terminal disclaimers cannot be established from the claim text alone.

2) Overlap risk inside the same chemical “neighborhood”

Even without the full formula drawings (##STR6##/##STR8##/##STR9##), the constraints indicate overlap concentration around:

aryl substitution variants with methyl and bromine in constrained roles; and
the same core scaffold where only n takes values 0-2.

That means other patents (if present) would likely cluster by:

alternative bromine/methyl regiochemistry,
variations where n = 0-2 but the linkage or substitution pattern changes only slightly,
and formulation patents that add reducing agents.

3) Competition map for potential “stannous reducing agent” formulations

Composition claims with a required stannous reducing agent tend to be copied by competitors only when the therapeutic mechanism is tied to reduction of an oxidized species or redox cycling. If competitors use the same redox formulation approach but swap in compounds outside claims 1/3, they may still avoid infringement of compound claims but potentially still face indirect overlap if their compounds land inside claims 1/3.

Claim chart: what each claim covers in infringement-ready terms

Claim	Claim type	Must include compound?	Must include stannous reducing agent?	Must satisfy R2/R3 rule	Must satisfy n
1	Compound	Yes	No	one is methyl, other is bromine	0, 1, or 2
2	Compound (dependent)	Yes	No	one is methyl, other is bromine	0
3	Compound	Yes	No	(implied by formula context; text omits R2/R3 sentence in provided excerpt)	0, 1, or 2
4	Composition	Yes	Yes	one is methyl, other is bromine	0, 1, or 2
5	Composition (dependent)	Yes	Yes	one is methyl, other is bromine	0
6	Composition	Yes	Yes	(text omitted in provided excerpt; formula-specific)	0, 1, or 2
7	Composition (dependent)	Yes	Yes	(text omitted in provided excerpt; formula-specific)	0
8	Species	Yes	No	embedded in named structure	fixed by species
9	Species	Yes	No	embedded in named structure	fixed by species

Key Takeaways

US 4,418,208 divides into two enforceable buckets: compound claims and composition claims that require a stannous reducing agent.
The compound class is tightly constrained: R2/R3 must be methyl and bromine (in either order) and n is limited to 0, 1, or 2.
Dependent claims further lock n = 0.
Claims 8 and 9 are exact species that define two concrete bisacetic acid-form compounds; these are direct infringement targets if marketed or manufactured in the covered forms.
Composition infringement is conditional on both formulation inclusion (stannous reducing agent) and active compound coverage under the Markush-defined scaffold.

FAQs

1) Does US 4,418,208 cover salts?

Yes. It covers “pharmaceutically acceptable, water soluble salt” forms of the claimed compounds (claims 1, 3, 4, 6).

2) What is the most important numerical limit in the Markush claims?

The integer parameter n is limited to 0, 1, or 2, with dependent claims fixing n = 0 (claims 2, 5, 7).

3) Is a stannous reducing agent required for infringement of the composition claims?

Yes. Claims 4 and 6 require “a composition comprising a stannous reducing agent” along with the claimed compound (claims 4 and 6).

4) Can a competitor avoid the composition claims by removing stannous reducing agent but keeping the compound?

Yes in principle. Composition claims require the stannous reducing agent; removing it avoids those claims but does not avoid the compound claims (claims 1-3, 8-9).

5) Are there exact named compounds in the claim set?

Yes. Claims 8 and 9 explicitly name two bisacetic acid-form compounds that function as species claims.

References

[1] United States Patent 4,418,208.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	377975	⤷ Start Trial
Austria	393357	⤷ Start Trial
Austria	A103384	⤷ Start Trial
Austria	A561381	⤷ Start Trial
Australia	539726	⤷ Start Trial
Australia	7880881	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,418,208

Summary for Patent: 4,418,208