United States Drug Patent 4,639,436: Claim Scope, Expiration, and Patent Landscape for Deoxynojirimycin Derivatives

U.S. Patent 4,639,436 covers a broad genus of substituted nojirimycin and 1-deoxynojirimycin compounds, including compounds corresponding to later commercial iminosugar drugs such as miglitol and miglustat. Its claims also cover pharmaceutical compositions, dosage forms, and methods for treating diabetes, hyperlipidaemia, and adiposity. The patent issued in 1987, and its ordinary United States patent term expired on January 27, 2004, assuming no unusual term adjustment or terminal disclaimer. It is no longer an enforceable United States patent barrier.

What does U.S. Patent 4,639,436 protect?

The patent protects three principal subject-matter categories:

Chemical compounds based on nojirimycin or 1-deoxynojirimycin scaffolds.
Pharmaceutical compositions and dosage forms containing those compounds.
Therapeutic methods using those compounds to treat diabetes, hyperlipidaemia, or adiposity.

The core independent chemical claim is Claim 1. It uses a highly expansive Markush structure for the substituent designated R1 and separately defines R2 and R3. The claim reaches a large chemical genus rather than a single active ingredient.

The patent also includes Claim 32, which separately identifies compounds in which R1 is C2-C18 alkenyl. Claims 11 through 17 identify specific compounds or structurally defined subgroups.

What chemical scaffold is covered?

The claims are directed to iminosugar derivatives of the nojirimycin family. The named compounds include:

N-methyl-1-nojirimycin
N-ethyl-1-nojirimycin
N-butyl-1-nojirimycin
N-benzyl-1-nojirimycin
N-allyl-1-nojirimycin
N-pentyl-1-deoxynojirimycin
N-hexyl-1-deoxynojirimycin
N-heptyl-1-deoxynojirimycin
N-octyl-1-deoxynojirimycin
N-nonyl-1-deoxynojirimycin
N-(beta-hydroxyethyl)-1-deoxynojirimycin
N-(beta-hydroxypropyl)-1-deoxynojirimycin
N-(5'-hydroxy-n-pentyl)-1-deoxynojirimycin
N-benzyl-1-deoxynojirimycin
N-propargyl-1-deoxynojirimycin
N-(2-methylmercaptoethyl)-1-deoxynojirimycin

The claim language also covers sulfonic acid, cyano, amino, hydroxymethyl, alkoxy, acylamino, sulfonamido, urea, thiourea, and carbamate substitutions.

How broad is Claim 1?

Claim 1 is the principal genus claim and is broad in four dimensions.

R1 substitution scope

R1 may be:

C5-C30 alkyl
C2-C18 alkenyl
C2-C18 alkynyl
C3-C8 cycloalkyl
C3-C8 cycloalkenyl
C3-C8 cycloalkynyl
Phenyl
Naphthyl
Phenyl-substituted alkyl
Substituted C1-C4 alkyl

The claim permits extensive substitution of those groups with hydroxy, alkoxy, amino, alkylamino, acylamino, mercapto, alkylthio, halogen, carbonyl, carboxyl, nitro, cyano, formyl, sulfo, and sugar-derived heterocyclic groups.

The practical effect is a broad lipophilic-to-polar substitution range. Long-chain alkyl groups can increase membrane interaction and enzyme-binding characteristics, while hydroxyalkyl and aminoalkyl groups create more polar derivatives.

R2 substitution scope

R2 is defined as a substituted or unsubstituted phenyl-containing group represented in the patent drawings. The allowed phenyl substituents are limited to:

Methyl
Ethyl
Methoxy
Chlorine
Bromine
Nitro

Claims 5, 6, and 9 narrow R2 to hydrogen, sulfonic acid, or cyano, with Claim 6 specifically selecting hydrogen.

R3 substitution scope

R3 may be hydrogen, methyl, hydroxymethyl, aminomethyl, substituted aminomethyl, alkoxymethyl, acyloxymethyl, sulfonamido-methyl, urea-derived methyl, thiourea-derived methyl, or carbamate-derived methyl.

Claims 7 through 9 narrow the group to selected hydrogen, methyl, hydroxymethyl, aminomethyl, and alkoxymethyl variants. Claim 8 specifically covers the hydroxymethyl derivative. Claim 9 combines R2 as hydrogen with R3 as hydroxymethyl.

Which claims cover miglitol and miglustat?

Does the patent cover miglitol?

Yes. Claim 14 expressly identifies N-(beta-hydroxyethyl)-1-deoxynojirimycin, the compound commonly known as miglitol.

Miglitol is an oral alpha-glucosidase inhibitor marketed in the United States as Glyset. The compound delays carbohydrate digestion and reduces postprandial glucose absorption. Claim 14 is a compound claim, while Claims 18 through 26 cover pharmaceutical compositions and dosage forms containing the claimed compounds, including tablets, capsules, ampoules, suppositories, pills, and dragees.[1]

The patent also reaches miglitol through broader genus Claims 1, 7, 8, and 9, subject to the structural formula represented in the patent drawings.

Does the patent cover miglustat?

The patent expressly lists N-n-butyl-1-desoxynojirimycin in Claim 11. That compound corresponds to miglustat, also known as N-butyldeoxynojirimycin.

Miglustat is an iminosugar used for substrate-reduction therapy in certain lysosomal storage disorders. Its later commercial indications differ from the diabetes, hyperlipidaemia, and adiposity indications recited in the method claims of Patent 4,639,436. The compound claims, however, are not limited to the listed therapeutic indications.

The distinction matters:

Claims 1 through 17 are principally compound claims.
Claims 18 through 26 are composition and dosage-form claims tied to diabetes, hyperlipidaemia, or adiposity.
Claims 27 through 31 are treatment-method claims directed to those same therapeutic categories.
A product may fall within a compound claim even if it is marketed for a different approved indication.

What formulations are protected?

Claims 18 through 26 create a formulation and dosage-form layer around the claimed compounds.

Composition claims

Claims 18 and 19 cover compositions containing an effective amount of a Claim 1 compound. The compositions may contain:

A solid diluent
A liquefied gaseous diluent
A liquid diluent
A sterile aqueous solution
A physiologically isotonic aqueous solution

Claim 18 excludes low-molecular-weight solvents below 200 molecular weight unless a surface-active agent is present. Claim 20 requires the active compound to constitute 0.5% to 95% by weight.

Claims 23 and 24 repeat this composition coverage for the stereochemically defined compound of Claim 17.

Dosage-form claims

Claims 21, 22, 25, and 26 cover medicaments in dosage-unit form with an inert pharmaceutical carrier. The listed dosage forms are:

Tablets
Pills
Dragees
Capsules
Ampoules
Suppositories

These claims are conventional formulation claims. They do not appear to require a particular release profile, particle size, salt form, excipient system, coating, manufacturing process, or pharmacokinetic profile.

The patent therefore has limited formulation specificity by modern pharmaceutical patent standards. Its formulation coverage depends primarily on using a claimed active compound in a conventional dosage form.

What method-of-use patents are included?

Claims 27 through 31 cover therapeutic administration to warm-blooded animals.

The listed treatment targets are:

Adiposity
Diabetes
Hyperlipidaemia

Claim 28 specifies a dosage range of 0.01 mg to 100 mg per kilogram of body weight per day. Claim 29 limits the animal to a ruminant, and Claim 30 specifies oral administration.

Claims 31 and related composition claims extend the same therapeutic concept to the stereochemically defined compound of Claim 17.

The method claims are broad in patient and disease language but narrow in their stated therapeutic purposes. They do not recite modern clinical parameters such as glycated hemoglobin reduction, postprandial glucose control, body-mass reduction, lipid parameters, or a specific patient subgroup.

How many patents cover the commercial compounds?

Patent 4,639,436 is one early foundational patent family covering a broad genus of iminosugar derivatives. It should not be treated as the complete patent estate for miglitol, miglustat, or related compounds.

Later commercial estates may include separate patents covering:

Improved synthetic processes
Crystalline forms
Salts
Polymorphs
Purification
Intermediate compounds
Formulations
Combination therapy
Specific clinical uses
Manufacturing controls

The supplied claim set does not establish those later rights. Patent 4,639,436 itself does not appear to claim a modern polymorph, specific crystalline form, controlled-release formulation, or commercial manufacturing process.

When did U.S. Patent 4,639,436 lose exclusivity?

The patent issued on January 27, 1987. For a United States patent subject to the pre-1995 term rule, the ordinary term was 17 years from issuance. On that basis, the ordinary expiration date was January 27, 2004.[2]

Event	Date or status
U.S. patent grant	January 27, 1987
Ordinary statutory term	17 years from grant
Ordinary expiration	January 27, 2004
Current enforceability	Expired
Current Paragraph IV relevance	None as a blocking patent
Current Orange Book barrier	None based on this expired patent

The patent cannot support a new United States infringement action for conduct occurring after expiration. Its claims remain relevant as prior art and as evidence of the historical scope of the invention, but not as an operative exclusivity right.

What is the Orange Book status of Patent 4,639,436?

Patent 4,639,436 is not a current enforceable Orange Book barrier. The Orange Book identifies patents submitted for approved drug products and uses those listings in abbreviated new drug application patent-certification procedures. An expired 1987 patent cannot delay generic approval through a current 30-month stay.

For products such as Glyset or miglustat products, any operative Orange Book analysis must focus on later patents associated with the relevant approved NDA, not on Patent 4,639,436. A generic applicant would not face a current Paragraph IV risk from this patent because its statutory term has ended.[3]

Which companies challenged or litigated this patent?

The supplied record does not identify an asserted case, ANDA challenge, settlement, or license involving Patent 4,639,436. Because the patent expired in 2004, current litigation risk is zero as to the patent itself.

No present Paragraph IV strategy can be based on this patent. Any historical challenge would have had to occur before expiration and would depend on the specific product, NDA, patent listing, and timing of the ANDA.

How strong is the patent estate?

Historical strength

The historical estate was strong at the genus level because Claim 1 combined:

A broad iminosugar core
Numerous R1 substituent classes
Multiple R2 and R3 options
Specific compound claims
Composition claims
Dosage-form claims
Treatment-method claims

Claims 11 through 17 provided fallback positions for named compounds and stereochemical embodiments. This structure would have given the patentee multiple infringement theories against a manufacturer producing a covered compound for the claimed therapeutic uses.

Current strength

The current legal strength is zero because the patent has expired. Its commercial value now lies in prior-art relevance and historical freedom-to-operate analysis.

The patent is also less likely to block modern development programs because it does not appear, from the supplied claims, to contain detailed protection for:

Specific polymorphs
Salt selection
Particle engineering
Modified-release systems
Combination products
Device-based delivery
Enantiomerically specific commercial formulations
Modern manufacturing routes

What generic entry risks exist?

Patent 4,639,436 creates no current generic-entry risk for an innovator and no current barrier for a generic applicant. Generic or follow-on developers may still need to assess:

Later compound patents
Product-specific formulation patents
Method-of-use patents
Orange Book-listed patents
Regulatory exclusivity
Pediatric exclusivity
Manufacturing patents
Foreign patent rights

For miglitol, the principal commercial risk today is likely competition from generic alpha-glucosidase inhibitors and other glucose-lowering therapies, rather than this expired patent. For miglustat, product-specific regulatory and manufacturing considerations may be more important than the early compound patent.

How does this patent compare with modern drug patents?

Patent 4,639,436 is broader chemically but less detailed technologically than many modern pharmaceutical patents.

Attribute	Patent 4,639,436
Primary subject	Chemical genus of iminosugar derivatives
Key compounds	Miglitol-type and miglustat-type derivatives
Formulations	Conventional dosage forms and solutions
Method of use	Diabetes, hyperlipidaemia, adiposity
Dose limitation	0.01-100 mg/kg/day in Claim 28
Manufacturing claims	Not evident in the supplied claims
Polymorph claims	Not evident
Current term	Expired
Current blocking value	None

The patent’s strongest historical feature was breadth across chemical substituents. Its weakest feature by current standards is the lack of detailed protection around commercial solid forms, process controls, and differentiated delivery systems.

Key Takeaways

U.S. Patent 4,639,436 covers a broad genus of nojirimycin and 1-deoxynojirimycin derivatives.
Claim 1 is the central Markush compound claim.
Claim 11 expressly includes N-n-butyl-1-deoxynojirimycin, corresponding to miglustat.
Claim 14 expressly includes N-(beta-hydroxyethyl)-1-deoxynojirimycin, corresponding to miglitol.
Claims 18 through 26 cover compositions and conventional dosage forms.
Claims 27 through 31 cover treatment of diabetes, hyperlipidaemia, and adiposity.
Claim 28 specifies administration of 0.01 mg to 100 mg per kilogram per day.
The ordinary patent term ended January 27, 2004.
The patent is not a current Paragraph IV or Orange Book barrier.
Later patents, regulatory exclusivities, processes, formulations, and geographic rights must be analyzed separately for any current commercial product.

FAQs About U.S. Patent 4,639,436

Does U.S. Patent 4,639,436 cover N-butyldeoxynojirimycin?

Yes. Claim 11 expressly lists N-n-butyl-1-deoxynojirimycin, the compound commonly known as miglustat or N-butyldeoxynojirimycin.

Does U.S. Patent 4,639,436 cover miglitol tablets?

The patent covers the miglitol compound through Claim 14 and covers tablets and other dosage forms through Claims 18, 21, and 22, subject to the claim limitations and the patent’s expiration.

Can an expired patent still be cited against a new drug application?

Yes. An expired patent can remain relevant as prior art, particularly to novelty and obviousness. It cannot, however, provide current enforceable exclusivity.

Does Claim 28 cover all oral dosing of deoxynojirimycin derivatives?

No. Claim 28 narrows the method to a defined dose range of 0.01 mg to 100 mg/kg/day. Claim 30 separately specifies oral administration. The method must also satisfy the disease and compound limitations inherited from the relevant claims.

Are European or Japanese equivalents still enforceable?

The United States expiration date does not determine foreign status. Each national or regional family member requires a separate analysis of grant, term, maintenance, supplementary protection, disclaimers, and any applicable term extensions.

References

U.S. Food and Drug Administration. (n.d.). Glyset (miglitol) prescribing information. FDA.
United States Patent and Trademark Office. (1987). U.S. Patent No. 4,639,436. Washington, DC: U.S. Department of Commerce.
U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations. FDA.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
Germany	27387173	Aug 27, 1977
Germany	27580252	Dec 24, 1977

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	373239	⤷ Start Trial
Austria	376420	⤷ Start Trial
Austria	376421	⤷ Start Trial
Austria	378771	⤷ Start Trial
Austria	A227183	⤷ Start Trial
Austria	A415383	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,639,436

Summary for Patent: 4,639,436