# United States Patent 5,057,616: Podophyllotoxin Purification Claims, Scope, Expiration, and Patent Landscape

U.S. Patent 5,057,616 covers a solid-adsorbent purification step for recovering podophyllotoxin from impure organic solutions. Its core inventive concept is contacting a podophyllotoxin solution containing an aliphatic halohydrocarbon with a high-surface-area inorganic adsorbent, removing the adsorbent, and recovering podophyllotoxin as a solid. The strongest claim coverage is directed to alumina, particularly neutral, acidic, or mildly basic alumina, used in a multistage purification process involving podophyllum resin, a lower alcohol, and a methylene chloride-acetone phase.[1]

The patent issued on October 15, 1991. Based on the pre-URAA 17-year term measured from grant, its U.S. patent term would have expired on October 15, 2008, absent a terminal disclaimer or an applicable patent-term adjustment. The patent therefore does not create current U.S. exclusionary rights. Its historical claim scope remains relevant to prior-art analysis, diligence, and interpretation of later podophyllotoxin manufacturing patents.

What does U.S. Patent 5,057,616 protect?

The patent protects a process for purifying podophyllotoxin rather than a podophyllotoxin composition, therapeutic use, dosage form, or finished pharmaceutical product.

The independent claims are claims 1 and 12.

Claim	Claim type	Principal subject matter
1	Independent process claim	Purification of podophyllotoxin from an impure solution in an aliphatic halohydrocarbon using a high-surface-area inorganic adsorbent
2	Dependent	Adsorbent is titania, boria, or alumina
3	Dependent	Adsorbent is alumina
4-8	Dependent	Addition of a polar aprotic cosolvent, including ketones, acetone, esters, or amides
9-11	Dependent	Neutral, acidic, or mildly basic alumina
12	Independent process claim	Multistage isolation of podophyllotoxin from podophyllum resin
13-19	Dependent	High-surface-area refractory oxide, especially alumina
20-22	Dependent	Lower alcohol, nonpolar liquid plus water, and optional acid in the first precipitation stage
23-24	Dependent	Halohydrocarbon plus polar aprotic liquid, specifically methylene chloride and acetone
25	Dependent	Additional dissolution and recrystallization stage

The claims do not require a particular purity percentage, yield, particle size, adsorbent loading, temperature, residence time, or crystallization solvent. Those omissions broaden the literal process language but can create validity and enablement questions if a challenger argues that the claims cover process conditions not adequately supported by the specification.

How does claim 1 define the protected purification process?

Claim 1 requires each of the following elements:

A process for purifying podophyllotoxin.
An impure solution containing podophyllotoxin.
A solvent comprising an aliphatic halohydrocarbon.
Recovery of podophyllotoxin as a solid.
Suspension of a high-surface-area solid inorganic adsorbent in the impure solution.
Adsorption of impurities by the solid.
Removal of the adsorbent.
Recovery of purified podophyllotoxin.

The claim is functionally drafted. The adsorbent must be capable of adsorbing impurities, but the claim does not identify the impurities or require a measured impurity reduction. The process must also include actual suspension of the adsorbent in the solution. A fixed-bed column, packed-bed filtration system, membrane, liquid-liquid extraction, or soluble scavenger would not necessarily satisfy the claim's literal "suspending" and "solid adsorbent" limitations.

What is the importance of the aliphatic halohydrocarbon limitation?

The solvent limitation is central. Examples of aliphatic halohydrocarbons may include methylene chloride, chloroform, dichloroethane, and related chlorinated hydrocarbons, depending on the specification's disclosure and claim construction.

A purification process conducted solely in methanol, ethanol, acetone, ethyl acetate, toluene, or water would not literally meet claim 1 unless the process also uses a qualifying aliphatic halohydrocarbon. Claim 1 does not require acetone. Acetone appears only in dependent claims 6 and 24.

What is the significance of the high-surface-area adsorbent requirement?

"High surface area" limits the claim to porous or finely divided inorganic solids used for impurity adsorption. The claim is not limited to a named commercial grade or a specific surface-area measurement.

The claim language distinguishes the invention from purification methods using:

Activated carbon, unless it could be characterized as the claimed inorganic adsorbent, which would be difficult because carbon is not an inorganic oxide in the ordinary claim context.
Soluble chemical reagents.
Liquid-liquid extraction without a suspended solid.
Crystallization alone.
Chromatographic resin systems.
Filtration media that do not adsorb impurities.

The functional language may allow a patentee to argue that a nonlisted inorganic material is covered if it has the required surface area and adsorbs impurities. That argument would be constrained by the claim's express inorganic-solid requirement and by prosecution history.

What additional compounds and materials are covered by claims 2 through 11?

Claims 2 through 11 progressively narrow the adsorbent and solvent system.

Claim group	Limitation	Commercial significance
Claims 2-3	Titania, boria, or alumina; then alumina	Establishes the principal oxide-based process
Claims 4-8	Polar aprotic cosolvent; ketone, acetone, ester, or amide	Covers solvent systems designed to modify solubility and crystallization behavior
Claims 9-11	Neutral, acidic, or mildly basic alumina	Covers alumina grades with different surface chemistry

The alumina claims are narrower than claim 1 but potentially easier to prove in an infringement analysis because the adsorbent identity can be established through procurement records, batch records, certificates of analysis, or process instructions.

The claims do not expressly require that the alumina remain in the vessel for a particular time or that it be removed by filtration. Any operation that removes the suspended solid may satisfy the removal limitation if the other elements are met.

What does claim 12 protect in the podophyllum resin process?

Claim 12 covers a two-stage isolation process:

Dissolving podophyllum resin in an organic solvent.
Adding a cosolvent to precipitate a first-stage podophyllotoxin product.
Recovering the first-stage precipitate.
Dissolving that product in an organic liquid phase containing an aliphatic halohydrocarbon.
Suspending a solid phase in the solution to produce a second-stage purified solution.
Recovering podophyllotoxin as a solid.

The claim contains an apparent drafting inconsistency in step e, which states that "the solid phase" is suspended. Claims 13 through 19 clarify that the intended material is a high-surface-area solid, specifically a refractory oxide such as alumina. Claim construction would likely read step e together with those dependent claims and the specification.[1]

Claim 12 is broader than claim 24 because claim 12 does not require methylene chloride and acetone. It is also broader than claims 16 through 19 because it does not expressly limit the refractory oxide to alumina or specify its acid-base character.

How do claims 13 through 25 narrow the process?

The dependent claims create several commercially relevant subgroups.

Refractory oxide claims

Claims 14 and 15 identify a refractory oxide selected from boria, titania, and alumina. Claim 16 narrows the material to alumina. Claims 17 through 19 cover neutral, acidic, and mildly basic alumina.

These claims create a practical infringement pathway where a manufacturer uses alumina in a second-stage methylene chloride or similar purification solution, even if the initial resin precipitation conditions differ from the examples.

Initial extraction and precipitation claims

Claim 20 requires a lower alcohol in the initial organic solvent. Claims 21 and 22 require a nonpolar organic liquid plus water as the cosolvent, with claim 22 adding an acid.

These limitations may cover a specific method for selectively precipitating a podophyllotoxin-rich intermediate from podophyllum resin. The claims do not identify a particular lower alcohol, nonpolar liquid, water concentration, or acid.

Methylene chloride-acetone claim

Claim 24 is the most specific solvent claim. It requires an organic liquid phase comprising CH2Cl2 and acetone at the stage where the first-stage product is redissolved before adsorbent treatment.

A process using methylene chloride and acetone, alumina, and the claimed resin-to-intermediate sequence would present the closest historical literal overlap with the patent's core examples.

Final recrystallization claim

Claim 25 adds a third-stage operation:

Dissolving purified podophyllotoxin in a solvent.
Recovering pure podophyllotoxin as a recrystallized solid.

The claim does not specify the third-stage solvent or the number of recrystallizations. It requires the additional recrystallization sequence, so a process stopping after adsorbent treatment and solid recovery may fall outside claim 25 while remaining within claim 1 or claim 12.

When did U.S. Patent 5,057,616 lose exclusivity?

The patent issued October 15, 1991. For a pre-June 8, 1995 application governed by the former 17-year term from grant, the ordinary expiration date was October 15, 2008.[1][2]

Event	Date or status
U.S. patent grant	October 15, 1991
Ordinary term basis	17 years from grant under the pre-URAA regime
Expected U.S. expiration	October 15, 2008
Current enforceability	Expired by term
Current Orange Book exclusivity	No drug-product exclusivity created by this process patent

The patent's expiration eliminates current U.S. infringement liability based solely on practicing the claimed process. It does not eliminate the patent's value as prior art against later applications or its relevance to patentability of improvements.

No current Paragraph IV challenge is required to practice the expired process. A generic or API manufacturer could use a process that would have fallen within the claims without seeking a license from the expired patent holder.

What is the Orange Book status of U.S. Patent 5,057,616?

The patent is a process patent for manufacturing or purifying podophyllotoxin. It is not a patent directed to a drug product, dosage form, method of use, or approved labeling indication.

FDA Orange Book listing generally concerns patents submitted by an NDA holder that claim the approved drug substance, drug product, or method of use. A historical purification patent of this type would not ordinarily provide Orange Book-listed protection for etoposide, etoposide phosphate, podophyllotoxin, or a branded formulation.[3]

The patent therefore does not establish:

A Hatch-Waxman statutory stay.
A Paragraph IV litigation risk for a generic drug applicant.
Product-level exclusivity for etoposide or podophyllotoxin.
Patent protection for a finished dosage form.
Exclusivity over a therapeutic indication.

Its relevance is primarily at the active-pharmaceutical-ingredient manufacturing and process-development level.

Does the patent create biosimilar risk?

No. Biosimilar applications concern biological products under the Public Health Service Act. Podophyllotoxin is a small molecule, and products such as etoposide are regulated through the small-molecule drug pathway rather than the biosimilar pathway.[4]

The relevant competitive risks are generic-drug entry, API manufacturing competition, process patents, formulation patents, and method-of-use patents. A biosimilar challenge is not the appropriate regulatory framework.

Which companies could challenge or bypass the patent?

Because the patent expired in 2008, companies do not need to challenge it through Paragraph IV litigation. Historically, a podophyllotoxin API producer could have pursued one of four routes:

Use a noninfringing purification process, such as liquid-liquid extraction or a fixed-bed adsorbent process.
Use a different solvent system without an aliphatic halohydrocarbon.
Use a non-inorganic adsorbent or a different purification mechanism.
Challenge validity based on anticipation, obviousness, written description, enablement, or indefiniteness.

The patent's broadest practical limitation is the combination of an aliphatic halohydrocarbon solution and a suspended high-surface-area inorganic adsorbent. A process avoiding either feature would have presented a stronger design-around position.

What patent litigation and settlement agreements affected the patent?

The provided claim set establishes the patent's technical scope but does not establish a reliable litigation history, settlement agreement, terminal disclaimer, reexamination, or post-grant proceeding. The patent's expiration also means that any historical dispute would not create present U.S. launch restrictions.

A current diligence conclusion should therefore treat the patent as an expired process patent, not as an active litigation blocker. The absence of a present infringement right is distinct from the possibility that later patents separately cover podophyllotoxin extraction, etoposide synthesis, crystalline forms, formulations, or therapeutic uses.

How strong was the patent estate for podophyllotoxin purification?

The patent had moderate historical strength within a defined process niche.

Factor	Assessment
Core claim breadth	Moderate
Chemical-material specificity	Moderate to broad in claim 1; narrower in claims 2-11
Process sequence coverage	Stronger in claim 12 and its dependent claims
Product protection	None
Formulation protection	None
Method-of-use protection	None
Current U.S. enforceability	None because the patent term expired
Design-around availability	Material
API manufacturing relevance	High historically
Finished-drug commercial blocking power	Low

Claim 1 is broad enough to reach multiple oxide adsorbents and solvent combinations, but it depends on a specific process architecture. Claim 12 provides a more detailed resin-to-purified-product pathway and may have been more effective against manufacturers using the disclosed multistage sequence.

The absence of purity thresholds and quantitative operating conditions could support infringement allegations against a range of processes. The same breadth could have exposed the claims to prior-art and enablement challenges.

What manufacturing and intellectual-property barriers remain after expiration?

The expired patent removes one barrier but does not clear the entire podophyllotoxin or etoposide manufacturing landscape.

Relevant remaining barriers may include:

Patents on extraction from Podophyllum species.
Patents on semisynthetic conversion of podophyllotoxin to etoposide or etoposide phosphate.
Crystalline or polymorphic forms.
Injectable, oral, or liposomal formulations.
Stabilizers, excipients, and container systems.
Controlled-release or targeted delivery systems.
Therapeutic use claims.
Improvements in impurity removal and API crystallization.
Manufacturing trade secrets covering yields, impurity profiles, and scale-up conditions.
Regulatory requirements for API quality, residual solvents, elemental impurities, and genotoxic impurities.

Those rights must be analyzed separately from U.S. Patent 5,057,616. This patent does not protect a formulation, route of administration, indication, or biological activity.

How does this patent compare with product and formulation patents?

Protection category	Covered by U.S. 5,057,616?	Commercial effect
Podophyllotoxin molecule	No	No composition-of-matter protection
Etoposide molecule	No	No direct protection
API purification process	Yes	Historical manufacturing restriction
Podophyllum resin extraction	Partly, through claim 12's sequence	Limited to claimed process steps
Finished dosage form	No	No formulation exclusivity
Method of treatment	No	No indication exclusivity
Biologic or biosimilar product	No	Not relevant
Crystalline form	No express claim	Requires separate patent analysis
Recrystallization operation	Yes, only through claim 25's process combination	Historical process coverage

What generic launch scenarios existed, and what is the current position?

Before expiration, the principal launch scenarios were:

A generic API producer used a process that avoided the aliphatic halohydrocarbon limitation.
The producer used a different adsorbent technology.
The producer challenged validity or scope.
The producer obtained a license or negotiated a settlement.
The producer waited until the October 15, 2008 expiration date.

After expiration, the fifth scenario became the operative legal position. The patent no longer delays generic or API entry in the United States.

For current commercial planning, the main question is not whether a process infringes U.S. Patent 5,057,616. The relevant question is whether later, unexpired patents or confidential manufacturing know-how constrain the proposed process.

What is the geographic coverage of the patent?

U.S. Patent 5,057,616 provides territorial rights only in the United States. It does not establish protection in Canada, Europe, India, China, Japan, or other jurisdictions.

Foreign counterparts, if any, must be assessed separately by priority family, national-phase status, expiration, maintenance fees, and local patent-term rules. A U.S. expiration date cannot be automatically applied to a foreign family member.

Key Takeaways

U.S. Patent 5,057,616 covers a podophyllotoxin purification process using a suspended high-surface-area inorganic adsorbent.
The core solvent limitation is an aliphatic halohydrocarbon.
Alumina, including neutral, acidic, and mildly basic alumina, is the principal claimed adsorbent.
Claim 12 covers a multistage process beginning with podophyllum resin and ending with solid podophyllotoxin.
Claim 24 specifically covers methylene chloride plus acetone in the second-stage solution.
Claim 25 adds a third-stage dissolution and recrystallization step.
The patent issued October 15, 1991 and ordinarily expired October 15, 2008.
It is not a product, formulation, method-of-use, or biologic patent.
It does not create current Orange Book, Paragraph IV, or biosimilar risk.
Current diligence must focus on later process, API, formulation, crystalline-form, and therapeutic-use patents.

FAQs

Does U.S. Patent 5,057,616 cover podophyllotoxin itself?

No. The claims cover processes for purifying or isolating podophyllotoxin. They do not claim podophyllotoxin as a chemical composition.

Would alumina treatment in methanol infringe claim 1?

Not necessarily. Claim 1 requires an aliphatic halohydrocarbon solvent. Alumina treatment conducted only in methanol would not satisfy that express limitation, although the complete process and any other applicable claims would require separate analysis.

Does claim 24 require both methylene chloride and acetone?

Yes. Claim 24 narrows claim 23 by requiring an organic liquid phase comprising CH2Cl2 and acetone.

Can a company use the claimed purification process in the United States today?

The patent's ordinary term expired in 2008. The expired patent itself does not prevent current use of the claimed process in the United States.

Does the patent block an FDA-approved etoposide generic?

No. The patent does not claim etoposide, a dosage form, an approved indication, or a finished drug product. Any current barrier would have to arise from separate patents, regulatory exclusivity, or manufacturing requirements.

References

U.S. Patent No. 5,057,616. (1991). Process for purification of podophyllotoxin. United States Patent and Trademark Office.
Leahy-Smith America Invents Act, Pub. L. No. 112-29, 125 Stat. 284 (2011); Uruguay Round Agreements Act, Pub. L. No. 103-465, 108 Stat. 4809 (1994).
U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations. FDA.
U.S. Food and Drug Administration. (n.d.). Biosimilars and interchangeable biosimilars. FDA.

Details for Patent: 5,057,616

Summary for Patent: 5,057,616