Details for Patent: 6,319,926

United States Patent 6,319,926: What Is Claimed and Where It Sits in the Sleep-Drug Landscape

What does US 6,319,926 claim, in scope terms?

US 6,319,926 claims a specific drug substance and a specific administration use framed around enantiopurity (dextrorotatory isomer) to improve sleep in humans.

Core claimed method (Claim 1)

Claim 1 recites a method for improving sleep quality or sleep time comprising:

• Administering an “effective quantity” to a human of:
  • 6-(5-chloro-2-pyridyl)-5-[(4-methyl-1-piperazinyl)carbonyloxy]-7-oxo-6,7-dihydro-5H-pyrrolo[3,4-b]pyrazine, or a pharmaceutically acceptable salt thereof
• Drug form requirement:
  • administered “in the form of its dextrorotatory isomer”
  • and “essentially free of its levorotatory isomer.”

Functional result: improving sleep quality or sleep time.

Scope boundaries embedded in the claim

The claim is narrow in the two most litigation-relevant ways:

1. Enantiomer requirement (dextrorotatory only)

   • The claim does not cover mixtures that are not “essentially free” of the levorotatory isomer. The scope hinges on the enantiomeric purity concept embedded in the term “essentially free.”

2. Chemical identity requirement

   • The administered compound is a single, highly specific chemical structure name (including substitutions). The claim is not a class claim over other pyrrolo[3,4-b]pyrazine derivatives unless they fall literally under the exact name or are determined to be the same compound under claim construction.

What is not claimed

Based on the provided claim text, US 6,319,926 does not, on its face, claim:

• manufacturing processes
• formulation (tablets, suspensions, controlled-release) as a separate inventive step
• routes of administration beyond “administering… to a human”
• dosing regimens (mg, frequency) as structural claim elements
• a broader “sleep disorders” indication without the “improving sleep quality or time” framing

How does the enantiomer framing shape enforcement risk?

The key risk axis for competitors is whether their product’s active pharmaceutical ingredient (API) is:

• predominantly the dextrorotatory isomer, and
• meets the claim’s “essentially free” condition for the levorotatory isomer.

In practice, enforcement turns on measurable parameters:

• chiral purity of the marketed API
• whether salts are used (salt form can matter for literal scope depending on how courts treat salt as “pharmaceutically acceptable salt thereof” for claim coverage)
• whether the competitor uses the dextrorotatory isomer as the principal enantiomer while retaining only trace amounts of the levorotatory isomer.

What is the patent landscape implied by this claim type?

A claim structured as: (1) specific drug entity + (2) dextrorotatory/enantiopurity + (3) human sleep improvement method typically sits in a crowded landscape shaped by:

• prior patents on the racemate or other enantiomer(s) of the same chemical entity
• follow-on patents on enantiomeric isolation/purity
• formulation or polymorph patents for the marketed product (often separate families)
• regulatory-anchored exclusivity (even when not part of patent scope, it impacts entry timing)

However, the landscape cannot be fully and accurately mapped from claim text alone. What can be concluded strictly from the claim is the likely role of US 6,319,926 within the family strategy: it is a use patent anchored to a specific stereochemical form of a defined compound.

What does “essentially free of its levorotatory isomer” do to claim construction?

From a business risk perspective, this phrase:

• pushes the claim beyond a simple “use of the dextrorotatory isomer” and into an impurity/threshold concept
• makes the enforcement boundary dependent on evidence of enantiomeric composition.

That creates two competitive postures:

• Literal risk: if a competitor’s API contains an amount of levorotatory isomer that is not “essentially free,” the claim may not read on their product.
• Doctrine-of-equivalents risk: even if a competitor tries to reduce the levorotatory fraction, the range of what courts treat as “essentially free” can still determine whether small differences matter.

Where is this patent likely located in term-expiry terms?

US patents follow standard term rules from earliest effective filing dates, not from grant dates alone. With only the grant number provided and no filing history supplied here, a precise expiration date cannot be derived without the application details.

How to treat this patent in a freedom-to-operate (FTO) screen

Even without filing histories, US 6,319,926’s claim structure dictates an FTO screen focused on three elements:

1. Does the candidate product use the same chemical entity?

   • The structure name is the anchor. Any different substitution pattern likely avoids literal coverage.

2. Is it administered as the dextrorotatory isomer?

   • Racemic or predominantly levorotatory products are not the claimed form.

3. Is the levorotatory isomer “essentially free”?

   • This is the primary bypass lever for competitors. It is also the core litigation lever for the patentee.

Likely overlap with other patent types in the same program

Based on typical program architecture for stereochemically defined sleep agents, other nearby patent buckets often exist. The presence of US 6,319,926 suggests the program likely includes adjacent IP around:

• the same compound but in different stereochemical forms (racemate vs enantiopure)
• process for preparing the dextrorotatory isomer
• salt selection and drug substance specs
• later formulation and dosage form patents

Those adjacent patents are not enumerated here because no patent family data, assignee, or related publication identifiers were provided.

Claim 1 deconstruction: element-by-element

Key Takeaways

• US 6,319,926 claim scope is centered on a single defined compound used as the dextrorotatory isomer and essentially free of the levorotatory isomer, for a human sleep-improvement method.
• The highest-likelihood design-around lever is enantiomeric purity of the marketed API (meeting the “essentially free” standard).
• The highest-likelihood infringement pivot is whether a competitor’s product uses the same compound and is marketed/used in a way that fits the dextrorotatory/enantiopurity constraint.
• The claim reads as a use patent tied to stereochemical selection rather than a broad class claim.

FAQs

1. Does US 6,319,926 cover racemic mixtures?
   The claim requires administration “in the form of its dextrorotatory isomer” and “essentially free” of the levorotatory isomer, so racemic or non-compliant enantiomeric compositions do not fall within the claim as written.

2. Is salt form outside the claim scope?
   Claim 1 explicitly covers the compound “or a pharmaceutically acceptable salt thereof,” so salt form is within literal claim coverage if it is pharmaceutically acceptable and the enantiomeric conditions are met.

3. Does the claim require a specific dosing regimen?
   The provided claim text requires an “effective quantity” but does not specify dosing parameters, so the claim is not limited to a particular mg amount or schedule on its face.

4. What product characteristic most affects infringement risk?
   Enantiomeric composition is the main risk driver because the claim requires the dextrorotatory isomer and “essentially free” levorotatory isomer.

5. Is this patent limited to a formulation type?
   The claim text is method-based and does not require a specific dosage form or formulation feature in Claim 1 as provided.

References

[1] United States Patent No. 6,319,926. Claims (provided).