United States Drug Patent 4,818,816: Scope of Claims and Patent Landscape
What is US Patent 4,818,816 claiming, in operational terms?
US Patent 4,818,816 is directed to stereospecific chemical synthesis of protected heparin-like glycosaminoglycan condensation products (2 to 12 saccharide units) and method steps for selectively converting protecting groups into sulfates and/or phosphates and free amines, plus selected substantially pure oligosaccharide chain embodiments and an antithrombotic pharmaceutical composition containing a specific final compound.
The claim set is structured around:
- Glycosylation/condensation of heparin-like repeating units using protected donors/acceptors
- Control of anomeric linkage stereochemistry (1→4 alpha vs 1→4 beta) based on whether the uronic acid end is D-glucuronic or L-iduronic
- Protecting-group strategy split into semi-permanent, permanent, other protecting groups (carboxyl esters), and optionally temporary groups to enable iterative elongation
- Late-stage deprotection and functional-group installation to produce --O--SO3 (sulfate) and --O--PO3 (phosphate) substituents and conversion of glucosamine C2 nitrogen protecting groups to amine
- Final purified product claims covering specific “single structure” compounds (with formula drawings), purified chains, and at least one specific formula compound used in an antithrombotic composition
Why are the “scope” boundaries tight?
The claims do not only cover “heparin/LMWH oligosaccharides.” They are constrained by a multi-parameter combination:
1) Length: “from 2-12 saccharide units” in multiple claims.
2) Backbone identity: alternating D-glucosamine and uronic acid units “linked in the manner found in heparin.”
3) Uronic acid options: uronic acid units are limited to D-glucuronic acid and/or L-iduronic acid (and their protected derivatives).
4) Linkage type control:
- 1-4 alpha linkage is required in claims focused on condensation where the first/second protected saccharide roles align with the chosen uronic acid end.
- 1-4 beta linkage is required for D-glucuronic acid-based junctions in later claims.
5) Protecting-group architecture: semi-permanent vs permanent vs other (carboxyl ester) vs temporary groups are explicitly operationally defined by removal stability and non-migration conditions.
6) Functional groups: sulfate/phosphate installation is explicitly in later process claims, and sulfate groups can be the preferred functional groups in dependent claims.
7) Staged chemistry: several claims require two-step schemes (condense then treat precursors like 1,6-anhydro or 2,3-epoxy, then further deprotection and sulfation/phosphorylation).
8) Specific chemical enabling pieces: reactive groups at reducing end (e.g., halogen, O-lower imidoyl, orthoester), catalysts (silver/mercury salts), solvents (dichloromethane/dichloroethane), and nucleophiles (e.g., sodium azide) appear in dependent claim strata.
That stack means design-around is possible, but only if a competitor avoids the same protecting-group scheme + stereospecific linkage constraints + functional-group installation sequence, not just the final product.
What do the independent claims actually cover?
Independent claim 1: Condensation route with defined donors/acceptors and alpha 1→4 linkage
Claim 1 is a process for synthesizing a mucopolysaccharide condensation product (2-12 saccharides) by condensing:
- A first protected saccharide selected from:
- D-glucosamine unit, or
- heparin-manner oligosaccharide with alternating D-glucosamine and uronic acid, terminal D-glucosamine at reducing end
- With a second protected saccharide selected from:
- A uronic acid unit, or
- heparin-manner oligosaccharide with alternating units and terminal uronic acid at non-reducing end
It requires:
- formation of a condensation product having a 1-4 alpha linkage between the first and second protected saccharide
- uronic acids are D-glucuronic or L-iduronic
- nitrogen at glucosamine C2 is “nitrogen containing groups … treated to form an amine”
Scope-critical constraints:
- linkage stereochemistry is limited to 1-4 alpha in claim 1
- donor/acceptor selection is constrained to heparin-style alternating sequences and terminal units
- nitrogen is constrained at C2 of D-glucosamine
Independent claim 2: Protected heparinic condensation products with semi-permanent and permanent protecting groups, sulfate/phosphate functionality endpoint
Claim 2 is broader than claim 1 in protecting-group mechanics. It requires:
- synthesis of a protected heparinic condensation product (2-12 units)
- with:
- semi-permanent protecting groups removable in the presence of permanent groups
- permanent protecting groups stable and “do not migrate”
- other protecting groups that form esters at uronic acid carboxyl groups
- nitrogen containing groups at C2 convertible to amine
- condensation between:
- first protected saccharide: protected D-glucosamine unit or protected heparin-oligo with terminal D-glucosamine at reducing end and having a reactive group at C1 enabling stereospecific linkage
- second protected saccharide: protected uronic acid unit or protected heparin-oligo with terminal uronic acid at non-reducing end
- protected condensation product must have a 1-4 alpha linkage
Then it defines the later functional group set:
- functional groups installed are --O--SO3 or --O--PO3
- permanent protecting groups must be removable in presence of those functional groups without migration requirements being violated
This claim anchors the core “process patent” moat: specific multi-category protecting-group stability and stereospecific linkage enabling groups.
Independent claim 3: Conditional alpha/beta 1→4 linkage depending on uronic acid identity
Claim 3 is another process with similar protecting-group architecture but imposes a symmetric linkage outcome:
- condensation between protected heparin-type donor/acceptor building blocks with a reactive group enabling stereospecific linkage
- requires that the resulting protected product has:
- 1-4 beta linkage when the first saccharide is D-glucuronic acid (or oligosaccharide with terminal D-glucuronic acid)
- 1-4 alpha linkage when the first saccharide is L-iduronic acid (or oligosaccharide with terminal L-iduronic acid)
This makes claim 3 an explicit discriminator: it ties glycosylation stereochemical outcomes to uronic acid identity.
Independent claim 4: Two-step route using glucose derivative precursors (1,6-anhydro; 2,3-epoxy)
Claim 4 adds a specific precursor-to-protecting-group conversion scheme:
- first step: condense
- first protected saccharide is a protected uronic acid unit or heparin-oligo with terminal uronic acid at reducing end and reactive group at C1
- second protected saccharide is a glucose derivative D-glucosamine precursor with precursor groups:
- 1,6-anhydro and/or
- 2,3-epoxy
- initial linkage formation constraints are given (beta for glucuronic acid end; alpha for iduronic acid end)
- second step: treat precursor groups to generate semi-permanent and permanent protecting groups at specific positions:
- 1,6-anhydro precursor is treated to form semi-permanent/permanent protecting groups at carbons 1 and 6
- 2,3-epoxy precursor is treated to form protecting group at carbon 3 and nitrogen-containing group at carbon 2
- then late-stage functional group introduction:
- install --O--SO3 or --O--PO3
- convert nitrogen to amine
- other protecting groups form ester at uronic acid carboxyl and are stable during condensation
Dependent claims 5-10 then detail acetolysis, epoxide opening with sodium azide, and conversion pathways.
Independent claim 23/24: “Can be elongated” version with temporary groups enabling iterative chain extension
Claims 23 and 24 are the elongation-enabling independent claim set:
- maintain semi-permanent/permanent/protecting-group stability requirements
- require temporary groups at specific positions that are removable in the presence of semi-permanent and permanent groups so the protected condensation product can be elongated
- explicitly allow formation of sulfate/phosphate functional groups and conversion to amines
They also preserve the linkage stereochemistry requirements (beta for D-glucuronic and alpha for L-iduronic in claim 24; alpha 1-4 in claim 23 as written).
Independent claim 31: Selective positioning of sulfate or phosphate groups
Claim 31 is a deprotection/re-functionalization process on a protected heparinic polysaccharide (2-12 units) with the same categories of protecting groups. It requires:
- remove semi-permanent groups
- replace them with --O--SO3 or --O--PO3
- remove permanent protecting groups and convert nitrogen protecting group to amine
Dependent claims 32-42 provide sulfate-preferred routes, including acetyl hydrolysis then sulfation, fractionation, and sodium ion exchange cleanup steps.
Independent claim 44/50/58/59/60/61: Substantially pure compounds, chains, and antithrombotic composition
- Claim 44: substantially pure compound of single structure selected from a set of formula drawings (marked “##STR56##”) with:
- variable R1 substituents
- semi-permanent groups stable through condensation
- permanent groups stable and non-migratory during semi-permanent removal and functional-group introduction
- M = carboxyl ester-forming group, stable during condensation
- N = nitrogen group convertible to amine
- R = temporary/permanent/reactive group category enabling elongation
- R’ = temporary/permanent/OH
- Claim 50: purified compounds with R constrained to “permanent protecting group” or inert blocking group
- Claim 58: substantially pure heparin chain, single structure, 2-12 units
- Claim 59: substantially pure oligosaccharide with alternating D-glucosamine and uronic acid units, and defines when --O--SO3 is positioned (not all) and explicitly defines linkage types:
- D-glucosamine to D-glucosamine junctions depend on uronic acid identity:
- linkages between D-glucosamine and uronic acid are of 1-4 alpha type
- and D-glucuronic to D-glucosamine are of 1-4 beta type (as written)
- Claim 60: a “synthetic pure compound of formula ##STR62##” (a single formula structure)
- Claim 61: antithrombotic pharmaceutical composition with pharmaceutically acceptable carrier and “the compound of claim 60”
How broad is the protection on “protected heparin” synthesis vs final active composition?
Scope that likely matters for R&D and freedom-to-operate
The patent is far more explicit about synthetic intermediates and protected structures than about one final named API. It grants process rights around:
- condensation chemistry
- linkage stereochemistry control
- protecting group behavior (stability and non-migration)
- precursor transformations (1,6-anhydro; 2,3-epoxy)
- functional group installation into sulfate/phosphate using deprotection sequencing
The final product protection exists, but claim language routes through “substantially pure” single-structure compounds with extensive parameterized substituent definitions, plus a specific formula claim used in an antithrombotic composition.
Practical implication
A competitor can potentially avoid infringement by altering:
- the protection chemistry categories (semi-permanent/permanent definitions and removal compatibilities)
- the stereospecific linkage mechanism (different donor activation and different anomeric control)
- the functional group installation order and protecting-group migration behavior
- or the precursor transformation logic (avoid 1,6-anhydro/2,3-epoxy acetolysis/epoxide opening schemes)
But avoiding only the final sulfated/phosphorylated oligosaccharide composition is less likely to be sufficient if manufacturing steps fall into the same stereospecific condensation and protecting-group strategy.
What do the dependent claims add (scope-limiting or scope-expanding details)?
Protecting group chemistry and specific functional conversion
- Claims 5-8 specify:
- acetolysis of 1,6-anhydro to obtain --O-acetyl semi-permanent groups
- epoxide opening with nucleophile (including sodium azide to install N3 at C2)
- alternatively benzylation of opened epoxide (permanent group at C3)
- Claims 9-10 specify:
- carbon 1 acetolysis product is replaced by a reactive group such as Br or Cl
- Claims 11-14, 25-27, 29-31, 33-36 constrain:
- sulfate-only preference (claim 11 and 32, 25 and 45-like descendants)
- semi-permanent and permanent group locations (notably at D-glucosamine carbons 3 and 6, and uronic acid carbons 2 and 3)
- example nitrogen protecting groups: N3; NH-acetyl (or NH-lower acyl); NHCO-benzyl (NHCO-lower arylalkyl)
Condensation conditions and catalysts
- Claims 15-17 specify condensation as halide + OH in solvent with catalyst:
- solvent: dichloromethane/dichloroethane
- catalyst salts: silver or mercury salts, including specific examples:
- trifluoromethane (as written), silver carbonate, silver oxide, mercuric bromide, mercuric cyanide
- Claims 18-19 cover reactive group types and temperature/solvent constraints:
- reactive group 1,2-O-methoxyethylidene
- boiling solvent above 100°C
- or O-lower imidoyl reactive group at temperature ≤ 0°C with catalyst
Temporary group categories for elongation
- Claims 23-24 and 27-30 add temporary protecting groups used for iterative chain building.
- Claims 29-30 enumerate temporary group categories, including --O-lower acyl, --O-allyl, --O-propenyl, halogenated acyl variants, and --O-p-methoxybenzoyl.
Functional group installation and workup
- Claims 40-43 provide a sequence:
- hydrolyze acetyl semi-permanent groups with strong base
- react with sulfation agent
- purify by fractionation
- optionally pass through sodium ion exchange column
Where does the patent sit in the broader heparin-like oligosaccharide patent landscape?
High-level positioning
Based on the claim architecture, US 4,818,816 aligns with a class of patents centered on:
- synthetic access to defined sulfated heparin-like oligosaccharides
- protecting-group strategies to control regioselectivity and stereochemistry in glycosylation
- iterative chain elongation to reach 2 to 12-unit structures
- late-stage conversion to sulfate/phosphate patterns compatible with biological activity
Likely competitive “adjacent” patent clusters
Within this technological space, competitor patents usually fall into one of three buckets:
1) Donor/acceptor activation and glycosylation stereocontrol for forming heparin-like 1→4 linkages
2) Protecting group systems (semi-permanent and permanent) with non-migration behavior across multi-step deprotections
3) Deprotection/functionalization methods to install sulfate/phosphate selectively and convert glucosamine C2 nitrogen to amine
US 4,818,816 covers all three, with unusually granular protection-category rules and explicit linker stereochemical mapping by uronic acid identity.
What are the main infringement vectors for a manufacturer?
1) Performing the same condensation to yield protected heparinic condensation products with required 1→4 alpha/beta stereochemistry and required donor/acceptor class selections.
2) Using the same protecting-group stability and non-migration framework, including:
- semi-permanent groups removable in presence of permanent groups
- permanent groups stable during semi-permanent removal and functional replacement
3) Using the same precursor transformation logic (claims 4-8) for building glucosamine donors:
- 1,6-anhydro to --O-acetyl semi-permanent
- 2,3-epoxy opening to install carbon-3 protection and C2 nitrogen (azide or equivalent)
4) Installing sulfate/phosphate with the same functional group types and sequencing steps (claims 31-43).
What are the main design-around levers?
Given claim language, the most direct design-around levers are:
- change from 1,6-anhydro and/or 2,3-epoxy precursor pathways (avoid claim-anchored precursor transformation steps)
- change anomeric stereospecificity control so the process does not produce the required 1-4 alpha or 1-4 beta linkage under the claimed donor/acceptor combinations
- replace the protecting-group system so that the semi-permanent/permanent categories do not meet the claim’s “stable and does not migrate” behavior constraints
- avoid forming a protected condensation product with the specific combination of:
- semi-permanent + permanent + carboxyl ester “other protecting groups” + C2 nitrogen types
- plus required reactive group at C1 reducing end
- avoid the specific purification/workup logic if a claim is tied to it (fractionation + sodium ion exchange), though most core scope is synthetic.
Key Takeaways
- US 4,818,816 is anchored in stereospecific glycosylation of heparin-manner alternating D-glucosamine and uronic acids (D-glucuronic and L-iduronic), producing protected condensation products 2-12 units.
- Claim scope is dominated by protecting-group system behavior (semi-permanent vs permanent vs temporary, stability, non-migration), plus explicit linkage stereochemistry rules tied to uronic acid identity.
- The patent spans condensation, elongation, and late-stage installation of sulfate/phosphate groups with conversion of C2 nitrogen to amines.
- A smaller but notable portion covers substantially pure single-structure oligosaccharides and a specific formula compound used in an antithrombotic composition.
FAQs
1) Is US 4,818,816 primarily a formulation patent or a manufacturing/process patent?
It is predominantly a manufacturing/process patent covering protected heparinic condensation products, protecting group strategies, and sulfate/phosphate installation steps.
2) What is the key stereochemical control point in the claims?
Formation of 1→4 alpha vs 1→4 beta linkages depends on the protected saccharide identities, especially the uronic acid unit being L-iduronic (alpha) vs D-glucuronic (beta) in the claim-3/4/24 framework.
3) How does the patent control sulfate vs phosphate functionality?
It explicitly restricts functional group installation to --O--SO3 and --O--PO3 in multiple process claims and includes dependent claims emphasizing sulfate.
4) Does the patent cover chain elongation beyond single condensation?
Yes. Claims 23/24 and related dependents require temporary groups removable to enable iterative elongation, while preserving semi-permanent/permanent protecting group integrity.
5) Does the patent claim final active oligosaccharides?
It includes claims for substantially pure, single-structure compounds and a synthetic pure formula compound (claim 60) used in an antithrombotic composition (claim 61), but the claim set heavily conditions those compounds through the described protecting-group and functional group frameworks.
References
[1] US Patent 4,818,816, “Process for synthesizing mucopolysaccharide condensation products” (claims provided in prompt).
