US Patent 5,900,488: Scope, Claims, and US Patent Landscape
What does US 5,900,488 claim in the US market?
US 5,900,488 claims an optically defined small-molecule antifungal active and three principal claim groupings: compound, composition, process, and method-of-use. The patent’s enforceable scope in the US is centered on the specific stereochemical identity and the specific therapeutic indication of mycosis.
Core active ingredient (claim 1)
- Claim 1: R-(-)-(E)- 4-(2,4-Dichlorophenyl)-1,3-dithiolan-2-ylidene!-1-imidazolylacetonitrile (or a pharmaceutically acceptable salt).
This is the anchor for the rest of the claims. The compound is defined by:
- absolute configuration: R
- optical rotation: (-)
- double-bond geometry: (E)
- structural substituents: 2,4-dichlorophenyl and imidazolylacetonitrile appended to a 1,3-dithiolane (thioketal-type) motif.
Composition scope (claim 2)
- Claim 2: A pharmaceutical composition with the active ingredient above plus a pharmaceutically acceptable carrier or diluent.
This claim is formulation-based and does not require any specific excipients beyond “acceptable carrier or diluent,” which can broaden literal coverage to most conventional dosage forms, provided the active identity matches claim 1.
Manufacturing scope (claim 3)
- Claim 3: A process producing the active (formula B) by reacting:
- an optically active glycol derivative (formula II) with
- a dithiolate salt (formula III)
Key process limitations:
- Reaction is between formula (II) glycol derivative and formula (III) dithiolate salt.
- X1 and X2 in the dithiolate are each the same or different and are selected from:
- methanesulfonyloxy
- benzenesulfonyloxy
- p-toluenesulfonyloxy
- halogen
- M is an alkali metal in the dithiolate salt.
This claim is structurally specific and method-limited. It is not a “generic” dithiolane formation; it ties enforceable coverage to the specific reactant classes and substitution options for X1/X2 and the alkali metal salt form.
Use/therapy scope (claim 4)
- Claim 4: Method for preventing or treating mycosis in humans or animals by administering a pharmaceutically effective amount of the active (or acceptable salt).
The therapeutic term “mycosis” is broad across fungal indications, but it is still limited to the claim-defined administration of this exact active/salt.
How broad are the enforceable boundaries across compound, salt, and stereochemistry?
US 5,900,488 is not “class” broad in the way that covers “any dithiolanylimidazolylacetonitrile analog.” Instead, it is precision-defined.
Stereochemical gating
Because claim 1 is defined as R-(-)-(E), enforceability will typically require a product to match:
- R configuration at the relevant stereocenter,
- the (-) enantiomer (as a practical matter, absolute stereochemical identity),
- E geometry at the relevant double bond.
That substantially narrows literal infringement for racemates, opposite enantiomers, or Z isomers. Unless a court construes “(-)” as something other than an enantiomeric requirement, third-party products that shift stereochemistry are the most direct carve-out risk.
Salt coverage
“Pharmaceutically acceptable salt” extends coverage beyond the free base. This can matter for:
- commercial salt selection (formulation choice),
- generics making alternate salt forms.
However, salt coverage does not erase stereochemical and structural constraints. Salt form does not change the underlying stereochemical and structural identity.
Formulation coverage
Claim 2 is broad to carriers/diluents. Literal infringement risk is highest when:
- the marketed composition includes the claimed active (or acceptable salt),
- the carrier is conventional.
If a competitor uses a different active, claim 2 does not apply. If a competitor uses the same active but a different dosage form, claim 2 still typically captures it, since “composition” is not tied to specific pharmaceutical form.
Process coverage
Claim 3 provides meaningful manufacturing leverage. It is enforceable against producers who practice the claim-limited route using:
- the specified glycol derivative (formula II),
- the specified dithiolate salt class (formula III),
- with X1/X2 options limited to methanesulfonyloxy, benzenesulfonyloxy, p-toluenesulfonyloxy, or halogen,
- and with alkali metal M as the salt counterion.
This matters because competitors can avoid process claims by using alternative synthetic routes. Even when the final active matches claim 1, process avoidance can reduce exposure to claim 3 while not eliminating compound and method-of-use risk.
What is the practical “claim scope map” for portfolio and litigation planning?
Below is a direct mapping of the four claims to product and manufacturing vectors.
| Claim |
What it covers |
What a competitor must do to infringe literally |
Typical avoidance levers |
| 1 (Compound) |
The exact R-(-)-(E) active (and pharmaceutically acceptable salts) |
Manufacture or sell the same stereochemically defined active/salt |
Use a different enantiomer/isomer; change core structure |
| 2 (Composition) |
Formulation containing the claimed active/salt + acceptable carrier |
Sell any dosage form with the claimed active/salt |
Replace active with non-claim compound |
| 3 (Process) |
Specific route using glycol derivative (II) + dithiolate salt (III) with X1/X2 constraints |
Practice the claim-limited steps and reactant selections |
Switch to alternative chemistry or protect/deprotect scheme outside claim limits |
| 4 (Method) |
Preventing or treating “mycosis” by administering this active/salt |
Market with fungal therapeutic use and administration instructions |
Avoid making/labeling for “mycosis”; change active |
How does the patent posture likely interact with US regulatory exclusivity (and where the real risk sits)?
In the US, enforcement of compound claims typically governs most value. For a fungally targeted product, compound claim 1 and method claim 4 drive infringement narratives around:
- generic substitution and ANDA filings (if present),
- branded product defense,
- label and promotional claims.
Process claims (claim 3) matter more in:
- manufacturing audits,
- biosynthesis-style evidentiary disputes in chemistry-intensive cases,
- counterclaims or disputes over “what route was actually used” to make the active.
Composition claims (claim 2) usually have less strategic leverage than claim 1 because a formulation is usually inseparable from the active itself.
US patent landscape: how to position related filings around a single stereochemically defined antifungal
A practical US landscape review centers on three axes:
- Related chemical family filings (same active, salts, isomers, polymorphs, stereochemical variants)
- Formulation and delivery filings (dosage forms, excipient systems, salts, particle size)
- Synthesis/process filings (alternative routes, different dithiolate salt forms, different activating groups X1/X2)
However, the only information provided here is the claims text. Without the bibliographic and prosecution details (assignee, filing date, publication number, family members), an accurate construction of the full US landscape (including which continuations exist, which related patents cite or are cited, and which expired or active US documents overlap) cannot be completed to a professional standard.
Per the constraints, no incomplete landscape mapping is produced.
Claim construction priorities for 5,900,488 (what will matter most in infringement and validity)
Even without full specification access, the claim text itself forces several key interpretive points that typically dominate US litigation and claim charts.
1) “R-(-)-(E)”
This is the tightest gate. Claim 1’s stereochemical triple specification is likely to be construed as requiring the compound to be the R enantiomer with the (E) geometry and matching optical identity as recited.
Impact: narrows potential design-around by stereochemical substitution.
2) “pharmaceutically acceptable salt”
This term is broad in practice, but it does not expand beyond salts of the claimed compound.
Impact: affects generic and lifecycle strategies (salt switching alone does not change underlying chemical identity).
3) Process definition by reactant formulas and X1/X2 options
Claim 3 explicitly limits the dithiolate salt substituents (X1/X2) to a defined list (methanesulfonyloxy, benzenesulfonyloxy, p-toluenesulfonyloxy, or halogen) and requires an alkali metal (M).
Impact: competitors can reduce process risk by selecting different leaving groups or salt forms that fall outside the listed options, or by using a different synthetic logic that does not meet the formula-defined reactant set.
4) “mycosis” in method claim 4
“Mycosis” is broad but still a therapeutic limitation.
Impact: label wording and promotional claims influence infringement theories under the method claim.
Key Takeaways
- US 5,900,488 is a stereochemically tight antifungal patent anchored on R-(-)-(E)-4-(2,4-dichlorophenyl)-1,3-dithiolan-2-ylidene!-1-imidazolylacetonitrile (and pharmaceutically acceptable salts).
- The enforceable scope is split across compound (claim 1), formulation (claim 2), synthesis route (claim 3), and therapeutic use for mycosis (claim 4).
- Stereochemistry is the primary boundary limiting literal infringement; salts broaden coverage but do not change the structural stereochemical requirements.
- The process claim (claim 3) is limited by specific reactant formula classes and by enumerated leaving-group/salt substituent options (X1/X2 and alkali metal M), creating a practical design-around path centered on synthetic route changes.
- A complete US landscape mapping cannot be produced from claims text alone; the landscape must be anchored to full patent bibliographic data and citation chains.
FAQs
1) Does claim 1 cover racemic mixtures or the opposite enantiomer?
Not on its face. Claim 1 requires R-(-) and (E), which gates coverage to the specified stereochemical identity.
2) Can a competitor avoid claim 2 by changing dosage form?
If the active/salt matches claim 1, claim 2 can still cover formulations because it only requires a pharmaceutically acceptable carrier or diluent.
3) Does “pharmaceutically acceptable salt” expand the claim to any salt?
It expands to salts that are pharmaceutically acceptable of the claimed compound, but it does not change the underlying stereochemical and structural definition.
4) What is the most likely lever to avoid infringement of claim 3?
Changing the synthetic route so that the reactants and/or the dithiolate salt features (X1/X2 leaving groups and M alkali metal salt form) no longer fall within the claim’s enumerated definition.
5) How do labeling and promotional statements interact with claim 4?
Because claim 4 is a method for preventing or treating mycosis, marketing that does not assert or instruct fungal therapeutic use can reduce exposure under that method claim framework.
References
[1] US Patent 5,900,488.
