United States Patent 8,420,656: Riociguat Claims, Scope, Expiration, and Patent Landscape
US Patent 8,420,656 covers riociguat and closely related substituted pyrazolopyridine compounds, together with selected salts, N-oxides, manufacturing routes, pharmaceutical compositions, and combination products. The patent is associated with Bayer's soluble guanylate cyclase stimulator program and is relevant to Adempas, the FDA-approved riociguat product.
The strongest protection is the compound coverage, particularly claim 3's expressly named riociguat molecule and its listed salts. The process, formulation, and combination claims provide secondary enforcement positions but are narrower and easier to design around.
What drug does US Patent 8,420,656 protect?
The patent principally protects riociguat, chemically identified as:
Methyl {4,6-diamino-2-[5-fluoro-1-(2-fluorobenzyl)-1H-pyrazolo[3,4-b]pyridin-3-yl]pyrimidin-5-yl}carbamate.
Riociguat is an oral soluble guanylate cyclase stimulator. Bayer markets it in the United States as Adempas for:
- Chronic thromboembolic pulmonary hypertension, or CTEPH, in patients with persistent or recurrent disease after surgical treatment or inoperable disease.
- Pulmonary arterial hypertension, or PAH, to improve exercise capacity and delay clinical worsening.
The covered chemical architecture combines:
- A pyrazolo[3,4-b]pyridine core.
- A fluorine substituent on the heteroaromatic ring.
- A 2-fluorobenzyl group attached to the pyrazole nitrogen.
- A diaminopyrimidine substituent.
- A carbamate group at the pyrimidine-linked position.
FDA approved Adempas on October 8, 2013. The approval was based on separate clinical programs in CTEPH and PAH. The FDA label identifies riociguat as a soluble guanylate cyclase stimulator and carries important contraindications relating to pregnancy and concurrent phosphodiesterase-5 inhibitor or nitrate use (U.S. Food and Drug Administration, 2023).
What are the claims of US Patent 8,420,656?
| Claim |
Subject matter |
Commercial relevance |
| 1 |
Broad compound Markush claim covering formula I compounds, N-oxides, salts, and salts of N-oxides |
Primary genus protection |
| 2 |
Narrower R1 definition limited to hydrogen, methyl, or trifluoromethyl-substituted methyl |
Intermediate species protection |
| 3 |
Nine expressly identified compounds and salts, including riociguat and specified acid-addition salts |
Strongest literal compound protection |
| 4 |
Three alternative manufacturing routes for formula I-A and I-B compounds |
Process and supply-chain protection |
| 5 |
Pharmaceutical formulation containing a claim 1 compound and excipient |
Product-composition protection |
| 6 |
Combination composition with specified cardiovascular or metabolic agents |
Combination-product protection |
| 7 |
Separate compound claim covering an illustrated formula and salts |
Scope depends on the omitted structural drawing |
Claim 7 cannot be structurally evaluated from the text supplied because its formula is represented only by an image placeholder. It should not be assumed to be coextensive with claim 3.
How broad is claim 1?
Claim 1 covers a genus of compounds defined by formula I. Its variable R1 may be:
- Hydrogen.
- A C1-C4 alkyl group.
- A C1-C4 alkyl group substituted by one or two fluorine atoms or trifluoromethyl groups.
The claim also extends to:
- N-oxides.
- Salts.
- Salts of N-oxides.
The practical scope depends on the unidentified fixed portions of formula I. Based on the dependent claims and named compounds, the genus is directed to substituted pyrazolopyridine-pyrimidine compounds incorporating the riociguat pharmacophore.
Claim 1 is broader than a claim limited to riociguat. It potentially covers analogues differing at the carbamate nitrogen substituent, including:
- The unsubstituted carbamate, corresponding to R1 = hydrogen.
- The N-methyl carbamate.
- The N-(2,2,2-trifluoroethyl) carbamate.
- Other permitted C1-C4 alkyl variants bearing fluorine or trifluoromethyl substituents, subject to the formula and specification support.
The principal legal risks for a broad genus claim would involve written description, enablement, anticipation, obviousness, and claim-construction disputes concerning the formula and substituent definitions.
What compounds are expressly protected by claim 3?
Claim 3 lists nine compounds or salt forms. The first three are neutral or differently N-substituted carbamates:
- Riociguat, the methyl carbamate.
- The N-methyl carbamate analogue.
- The N-(2,2,2-trifluoroethyl) carbamate analogue.
The remaining six entries are salts of riociguat:
- Hydrochloride.
- Sulfate.
- Phosphate.
- Mesylate.
- Ethane-1,2-disulfonate.
- Maleate.
- Nitrate.
The claim text identifies nine entries, although the listed categories comprise three non-salt or substituted-carbamate compounds plus seven named salt forms if each salt is counted separately. The supplied claim should be checked against the issued patent PDF for punctuation and enumeration because the salt list may contain a drafting or transcription discrepancy.
Salt coverage matters commercially because a generic applicant may attempt to use a different solid form or counterion. A product containing the same active moiety may still raise infringement issues under claim 1 or claim 2 even if it avoids the specific salt named in claim 3.
What manufacturing processes does patent 8,420,656 cover?
Claim 4 contains three alternative route descriptions.
Route A: Stannane-palladium coupling
The first route uses:
- A compound of formula II.
- Hexabutyltin.
- A palladium catalyst.
- A compound of formula III.
- Reduction of an intermediate.
- Reaction with methyl chloroformate.
This route produces compound I-A, the methyl carbamate form.
The route resembles a Stille-type cross-coupling strategy. Its commercial value is significant if the claimed sequence is used in manufacturing, but it does not necessarily block all alternative routes to riociguat. A manufacturer using a different coupling partner, catalyst system, intermediate order, or carbamate installation sequence may avoid literal infringement.
Route B: Copper-cyanide and acidic conversion
The second route uses:
- Copper cyanide conversion of formula II to formula VI.
- Acidic conversion to formula VII.
- Reaction with formula VIII in the presence of a base.
- Reduction to compound V.
- Carbamoylation under route A.
This route protects a distinct synthetic sequence. It may be more relevant to process validation and historical manufacture than to product-level generic entry.
Route C: Alkylation of compound I-A
The third route converts I-A into I-B using:
- A base.
- An alkylating reagent R1A-X1.
- A leaving group such as bromide, iodide, mesylate, tosylate, or trichloromethanesulfonate.
This route covers preparation of N-substituted carbamates, including the N-methyl and N-(2,2,2-trifluoroethyl) analogues.
Process claim 4 is vulnerable to design-around because it is dependent on specific reaction sequences and reagent classes. It is more useful for supply-chain investigations than for blocking every route to the active ingredient.
What formulation protection does patent 8,420,656 provide?
Claim 5 covers a pharmaceutical formulation containing:
- A compound of claim 1.
- An inert, non-toxic, pharmaceutically suitable excipient.
This is a functional formulation claim with limited technical detail. It does not recite:
- A specific tablet composition.
- A dissolution profile.
- A release mechanism.
- A particle-size range.
- A crystalline form.
- A particular dosage strength.
- A specific manufacturing process.
Because of that breadth, claim 5 may read on ordinary immediate-release oral dosage forms containing riociguat. Its enforceability would depend on claim construction and validity analysis. At the same time, its lack of formulation specificity may make it more exposed to prior-art and enablement arguments than a narrowly drafted formulation patent.
The claim does not by itself establish protection for a particular commercial Adempas tablet strength. Separate patents or regulatory listings may be required to establish product-specific formulation coverage.
What combination products are covered?
Claim 6 covers compositions containing a claim 1 compound plus an additional active agent selected from:
- Organic nitrates.
- Nitric oxide donors.
- cGMP phosphodiesterase inhibitors.
- Antithrombotic agents.
- Blood-pressure-lowering agents.
- Lipid-metabolism agents.
The claim is broad in therapeutic category but is subject to the requirement that both the riociguat-related compound and the additional active compound be present in the pharmaceutical composition.
The claim has limited commercial value for Adempas because the FDA label contraindicates coadministration with nitrates, nitric oxide donors, and PDE-5 inhibitors in relevant circumstances. A broad patent claim does not override FDA labeling or clinical safety restrictions.
When does US Patent 8,420,656 lose exclusivity?
| Event |
Date or status |
| Earliest priority |
Reported priority in the patent family: March 30, 2007 |
| U.S. patent grant |
April 16, 2013 |
| Nominal 20-year term |
Approximately March 30, 2027, subject to patent-term adjustments or extensions |
| FDA approval of Adempas |
October 8, 2013 |
| New chemical entity exclusivity |
Approximately five years from approval, subject to FDA calculation |
| Orphan-drug exclusivity |
Applied to qualifying indications and runs separately from patent term |
| Earliest conventional generic-entry window |
Governed by patent term, regulatory exclusivity, litigation, and any settlement |
The exact expiration date must be taken from the USPTO patent-term record and the FDA Orange Book listing. Patent expiration cannot be calculated solely from the grant date. A terminal disclaimer, patent-term adjustment, patent-term extension, or corrected priority chain could change the effective date.
US Patent 8,420,656 is not the only possible barrier to generic riociguat. Later patents may cover formulations, crystalline forms, dosing regimens, methods of treatment, or manufacturing improvements.
What is the Orange Book status of riociguat?
Adempas is an FDA-approved small-molecule product, so Orange Book-listed patents, rather than the Purple Book, are the relevant FDA patent framework. The Orange Book may include patents submitted by the NDA holder that claim:
- The active ingredient.
- A drug product.
- A method of using the drug.
A generic applicant seeking approval through an abbreviated new drug application must address listed patents through one of four certifications:
- Paragraph I: no patent information is listed.
- Paragraph II: the patent has expired.
- Paragraph III: approval is deferred until patent expiration.
- Paragraph IV: the patent is invalid, unenforceable, or will not be infringed.
A Paragraph IV notice can trigger litigation under the Hatch-Waxman Act. The supplied patent text does not establish whether a specific generic applicant has filed a Paragraph IV certification or whether litigation is pending.
Which companies are challenging riociguat exclusivity?
The claim set identifies Bayer as the relevant originator-side patent owner or member of the Bayer patent estate. It does not identify a generic challenger, Paragraph IV notice, settlement agreement, or court decision.
Generic competition would most likely come from companies with ANDA capabilities in complex oral cardiovascular products. A challenger would need to address:
- Compound claims.
- Any later Orange Book-listed product or method claims.
- Salt and solid-form selection.
- Manufacturing-route differences.
- FDA bioequivalence requirements.
- Label carve-outs for patented indications, where legally available.
A noninfringing generic strategy could use the same riociguat active moiety in a salt or formulation that avoids narrower claims. That strategy would remain exposed if claim 1 covers the active compound regardless of salt selection.
How strong is the patent estate?
| Patent category |
Relative strength |
Reason |
| Named riociguat compound |
High |
Directly identifies the commercial active ingredient |
| Broad Markush genus |
Medium to high |
Broad scope, but more exposed to validity and construction challenges |
| Specific salts |
Medium |
Useful against salt-specific products; alternative salt strategies may exist |
| Manufacturing process |
Medium |
Enforceable only when the accused route practices the claimed sequence |
| Basic formulation |
Medium to low |
Broad but technically undetailed |
| Combination therapy |
Low to medium |
Broad categories, limited by clinical and labeling restrictions |
| Method of use |
Not established from supplied claims |
Claims 1-7 do not recite a therapeutic method |
The most important distinction is between direct compound protection and peripheral process protection. A generic product containing riociguat faces the greatest risk under claims 1-3, not claim 4.
How does riociguat compare with competing pulmonary-hypertension drugs?
| Drug |
Class |
Competitive relationship |
| Riociguat |
Soluble guanylate cyclase stimulator |
Directly stimulates sGC and is approved for CTEPH and PAH |
| Sildenafil |
PDE-5 inhibitor |
Increases cGMP by reducing its degradation |
| Tadalafil |
PDE-5 inhibitor |
Similar cGMP pathway but different dosing and patent estate |
| Selexipag |
IP receptor agonist |
Targets prostacyclin signaling |
| Macitentan |
Endothelin receptor antagonist |
Targets endothelin-mediated vasoconstriction |
| Treprostinil |
Prostacyclin analogue |
Vasodilator with oral, inhaled, subcutaneous, and intravenous products |
Riociguat has a differentiated mechanism, but it competes commercially with other PAH therapies and combination regimens. Its product-level patent exposure must be analyzed separately from market exclusivity because competing drugs are not substitutes for purposes of literal patent infringement.
What generic launch scenarios exist?
Launch after patent expiration
This is the lowest-litigation scenario if all relevant Orange Book patents have expired and no regulatory exclusivity remains.
Paragraph III filing
A generic applicant may acknowledge an unexpired patent and defer approval until the listed expiration date. This avoids immediate litigation but delays commercial entry.
Paragraph IV challenge
A challenger may assert that the patent is invalid, unenforceable, or not infringed. Litigation may trigger a 30-month FDA approval stay under the Hatch-Waxman framework, subject to statutory exceptions and court developments.
Carved-out labeling
A generic applicant may attempt to omit a patented method of use. This strategy has limited value against a composition-of-matter claim covering riociguat itself.
Alternative salt or formulation
A different salt, excipient system, or solid form may avoid selected dependent claims. It is unlikely to avoid a properly construed claim covering the active compound broadly.
Key Takeaways
- US Patent 8,420,656 is principally a riociguat compound patent associated with Bayer's Adempas franchise.
- Claims 1-3 provide the core protection, with claim 3 expressly naming riociguat and multiple salts.
- Claim 4 protects three manufacturing pathways but does not necessarily block alternative synthesis.
- Claim 5 covers broad pharmaceutical compositions but does not specify a particular commercial tablet formulation.
- Claim 6 covers combinations with cardiovascular and metabolic agents, although some claimed combinations may be clinically restricted.
- The nominal patent term points to 2027, subject to the official USPTO term calculation.
- Generic risk is highest for products containing riociguat itself, regardless of whether a generic uses a different manufacturing route.
- The supplied claims do not establish a current Paragraph IV challenge, litigation outcome, or settlement agreement.
- Claim 7 requires review of the issued structural drawing before its scope can be determined.
FAQs
Is US Patent 8,420,656 a patent on Adempas?
Yes. Its principal compound claims cover riociguat, the active ingredient in Adempas, together with related analogues and salts.
Does a different riociguat salt avoid this patent?
Not necessarily. Claims 1 and 2 cover salts broadly, while claim 3 lists specific salts. A different salt may avoid claim 3 but remain within the broader claims.
Can a generic manufacturer use a different synthesis route?
Potentially. A different route may avoid claim 4, but it would not avoid claims 1-3 if the resulting product is riociguat or another covered compound.
Does the patent claim pulmonary arterial hypertension treatment?
The supplied claims do not expressly recite a method of treating PAH or CTEPH. They claim compounds, processes, formulations, and combinations. Separate method-of-use patents would need independent review.
Is riociguat subject to biosimilar competition?
No. Riociguat is a synthetic small molecule. Competition proceeds through the ANDA generic-drug pathway, not the biologic biosimilar pathway.
References
Bayer HealthCare Pharmaceuticals Inc. (2023). Adempas (riociguat) prescribing information. U.S. Food and Drug Administration.
U.S. Food and Drug Administration. (2023). Orange Book: Approved drug products with therapeutic equivalence evaluations. Center for Drug Evaluation and Research.
U.S. Patent No. 8,420,656. (2013). Pyrazolopyridine compounds. United States Patent and Trademark Office.
U.S. Patent and Trademark Office. (2024). Patent term adjustment and patent term extension records. United States Department of Commerce.
