US 5122614

I'll search for authoritative information on this specific patent number.

US Patent 5,122,614 — Summary

Source of record: Google Patents full text of US5122614A, fetched 2026-09-28 from https://patents.google.com/patent/[US5122614](/patent/US5122614)/en (the authoritative text supplied in the research packet). Identifiers below are reproduced literally, without normalization.

Bibliographic data

Abstract (verbatim)

Poly(ethylene glycol)-N-succinimide carbonate and its preparation are disclosed. Polyethylene glycol (PEG) is converted into its N-succinimide carbonate derivative. This form of the polymer reacts readily with amino groups of proteins in aqueous buffers. The modified proteins have PEG-chains grafted onto the polypeptide backbone by means of stable, hydrolysis-resistant urethane (carbamate) linkages.

Plain-language overview of the independent claim

Only claim 1 is independent — claims 2–6 all depend from it. The granted claim set is entirely compound claims; the process and protein-conjugate subject matter recited in the specification's "Summary of the Invention" is not claimed in this patent (the process was later claimed in the continuation case US5808096A).

Claim 1 — the active PEG carbonate compound. A polyalkylene oxide (e.g., PEG) polymer chain whose terminal hydroxyl has been converted into a carbonate ester of an N-hydroxydicarboximide. In plain terms:

• The chain is R₁–[polyalkylene oxide]–O–C(=O)–O–R₅.
• R₁ is H–, H₃C– (i.e., methoxy-capped, "mPEG"), or a second oxycarbonyl-N-dicarboximide group (making the molecule bifunctional).
• R₂, R₃, R₄ are alkyl groups (straight or branched, may be the same or different) — i.e., the polymer can be poly(ethylene oxide), poly(propylene oxide), poly(butylene oxide) or copolymers thereof.
• R₅ is an N-dicarboximide group (the "leaving group" that activates the carbonate).
• a = 1–1000; b and c = 0–1000 each; a + b + c = 10–1000 (so the polymer must be an oligomer/polymer of at least ~10 alkylene oxide units).

The commercial significance: the terminal group (−O−CO₂−succinimide) reacts quickly with protein amine groups under mild aqueous conditions, and the polymer becomes attached to the protein through a urethane (carbamate) linkage, which the specification shows is far more hydrolysis-resistant than the ester linkage of the then-prior-art SS-PEG.

Dependent claims (sub-scope):

• Claim 2 — defines the alkylene units: –CH₂CH₂–, –CH₂CH(CH₃)–, or –CH₂CH₂CH₂CH₂–.
• Claim 3 — the N-dicarboximide(s) selected from N-succinimide, N-phthalimide, N-glutarimide, N-tetrahydrophthalimide, N-norbornene-2,3-dicarboximide (R₁ and R₅ may differ).
• Claim 4 — R₅ is specifically an N-succinimide group.
• Claim 5 — the monofunctional species mPEG–O–CO₂–succinimide / PEG–O–CO₂–succinimide ("SC-PEG"), with R₁ = H₃C– or H– and a = 10–1000.
• Claim 6 — the homobifunctional species succinimidyl-O–CO₂–PEG–O–CO₂–succinimide ("BSC-PEG"), a = 10–1000.

Litigation / CAFC 2026 docket check — important caveat

I searched for docket or appellate activity specifically tied to 5,122,614. I found no CAFC 2026 docket entry, and no active litigation, involving this patent number. I must flag this as a limitation rather than a negative finding of authority:

• My searches returned only patent-citation and prosecution-history material (Google Patents, Justia, PubChem, uspto.report, EPO/CN/RU documents citing US 5122614 A), plus Enzon corporate disclosures about other patents.
• The Enzon v. Shearwater Polymers and Enzon v. Roche disputes referenced in Enzon's 2001 press release concerned Enzon's branched PEG patents, which are not identified there as 5,122,614.
• Consistent with the record, the patent's anticipated expiration was 2009-06-16, so assertion of this patent in a 2026 proceeding would be unexpected absent unusual circumstances.
• I did not directly query the CAFC docket or USPTO PatentCenter/assignment databases for this number; my tool coverage was general web search over the fetched Google Patents record. Treat the "no 2026 activity" point as unverified rather than confirmed.

Minor discrepancies noted (interpreted literally, not corrected)

• One secondary source (Unified Patents portal) listed the priority date for the related US-5324844-A family member as 1989-04-18, whereas the Google Patents record for US07/511,243 states 1989-04-19. I have used 1989-04-19 (the value in the authoritative record) and am flagging the one-day discrepancy in the secondary source.
• A Russian citation (RU2176253C2) renders the issue date as 16.07.1992; the authoritative record gives 1992-06-16. I have used 1992-06-16.
• The specification's Summary of the Invention describes a process claim and a modified polypeptide claim; the granted claims (6 total) contain neither — all six are compound claims.

I'll search for litigation involving US patent 5122614.

Let me search litigation-specific databases.

Summary of Findings

I was unable to identify any litigation — district court, ITC, or Federal Circuit — specifically asserting or adjudicating U.S. Patent No. 5,122,614. Based on the searches I ran, I could not locate any docket entry, complaint, CAFC opinion, or litigation-database record tying that patent number to a case. I am reporting this as "no known litigation found" rather than as an absolute negative, because my searches were not exhaustive (see the caveats below).

What I searched

• General web searches for "5122614" and "5,122,614" combined with litigation/infringement terms.
• Searches aimed at the patent's assignee, Enzon (Enzon Pharmaceuticals / Enzon, Inc.), for patent suits.
• Searches targeting CourtListener/RECAP and PACER-style dockets.

What the searches actually returned (and why it is not litigation on '614)

Nearly all hits for "5122614" were patent citations, not litigation:

• Numerous later patents and published applications cite US 5,122,614 as prior art — e.g., EP2805965A1, EP2284191A2, EP2166076A1, US 8,048,408, US 9,187,569, CN100532546C, and Russian/Polish family members. Citations of a patent as prior art are not litigation.
• There were also several unrelated judicial opinions containing the string "5122614" only as part of a Westlaw citation (e.g., Okocha, 2010 WL 5122614, an FCRA case). These are false positives and have nothing to do with the patent.

One near-miss that must be flagged for accuracy: a real patent case, Enzon Pharmaceuticals, Inc. v. Phoenix Pharmacologics, Inc., D. Del. Case No. 1:04-cv-01285-GMS (filed 09/21/2004; terminated 03/06/2006; stipulated dismissal with prejudice). The court's own Patent/Trademark Report to the Commissioner identifies the patent-in-suit as U.S. Patent No. 6,183,738, not 5,122,614. So this case is not litigation on the '614 patent, and I am not counting it.

I also saw a reference to Enzon Pharmaceuticals, Inc. v. Nektar Therapeutics, 2016 NY Slip Op 06977 (N.Y. App. Div., decided Oct. 25, 2016) — a state-court contract/royalty dispute (concerning royalties on patents after expiration, citing Kimble v. Marvel). I could not confirm that U.S. 5,122,614 was among the patents at issue in that contract dispute, so I am not asserting it as '614 litigation.

Important contextual facts about the '614 patent

From the patent record itself (Google Patents, US5122614A):

• Assignee: Enzon, Inc. (later Enzon Pharmaceuticals, Inc.); inventor Shmuel Zalipsky.
• Priority date: 1989‑04‑19; filed 1990‑04‑19; granted 1992‑06‑16; anticipated expiration 2009‑06‑16; legal status "Expired – Lifetime."
• The '614 patent is in a family that includes US 5,324,844 (divisional), US 5,612,460, and US 5,808,096 ("Process for preparing active carbonates…"). Any litigation that did occur would most plausibly have been brought by Enzon during the 1990s–2000s and could have named one or more of these family members. I did not find a case naming '614.

Caveats / limitations

• I could not complete verification against the Unified Patents litigation portal or PACER directly (my searches hit a step limit and the tool set available to me is web search only, which does not authenticate into those dockets).
• Absence of a hit is not proof that no case exists; older pre‑2000 litigation and sealed/under-seal materials are often poorly indexed in free sources.
• My confidence is low-to-moderate that this is a complete negative. I recommend confirming with a direct query to the Unified Patents litigation search (portal.unifiedpatents.com/litigation), a PACER docket search or Docket Navigator, and a Westlaw/Lexis "cited patent" litigation check for 5122614, all of which index district-court complaints by patent number.

Bottom line: No litigation specifically involving U.S. Patent No. 5,122,614 was found. The one Enzon patent-infringement case I did surface (Enzon v. Phoenix Pharmacologics, 1:04-cv-01285-GMS) involved U.S. 6,183,738, a different patent, and is therefore not responsive to your request.

I'll start by checking the structured ODP-derived block against live sources.

Proceedings overview

Total AIA trial proceedings on file for US 5,122,614: 0 — zero IPRs, zero PGRs, zero CBMs (breakdown: 0 active / 0 claims invalidated / 0 claims sustained / 0 settled / 0 institution-denied). The USPTO Open Data Portal returns no AIA trial proceedings, and independent web searching surfaced none. The bottom line for a defendant is therefore not "hardened patent" and not "canceled claims" — it is a dead patent: all claims (1–6) stand unadjudicated, but the patent's term expired on 2009-06-16 and it is recorded as "Expired – Lifetime." An IPR-based invalidity defense is not merely unnecessary; there is no live infringement theory to defend against.

No proceedings to report

Because there are no proceeding numbers, there are no {PROCEEDING_NUMBER} — {Petitioner} v. {Patent Owner} entries to populate. I will not manufacture any. Every field in the requested per-proceeding template (judge panel, petition grounds, institution decision, FWD claim-level verdict, settlement, CAFC appeal) is empty by definition. Below I document why the docket is empty and what it means, which is the question that actually matters to a defendant.

• Canonical source: USPTO ODP structured "PTAB proceedings on file" block supplied in this prompt — empty.
• Corroborating check: web search for IPR/PGR/CBM activity tied to US 5,122,614, Enzon, and "active carbonates" returned no PTAB dockets, no FWDs, and no CAFC appeals arising from a PTAB trial. References to the patent in the wild (e.g., EP 1,078,006 B1; JP 2003-527090 A; RU 2,268,749 C2) are all citing art, not challenges.

Strategic summary

Claim status. All six claims of US 5,122,614 — claim 1 (the genus polyalkylene-oxide oxycarbonyl-N-dicarboximide compound), claims 2–4 (dependent, defining R²/R³/R⁴ and the N-dicarboximide species), claim 5 (mPEG-succinimidyl carbonate, "SC-PEG"), and claim 6 (the bis-succinimidyl carbonate, "BSC-PEG") — are UNTESTED before the PTAB. None are cancelled; none are sustained by any adjudicative body. That is a status, not a strength. The claims are also expired: the ODP record shows anticipated expiration 2009-06-16 and current legal status "Expired – Lifetime." The same is true of the family members that claim priority to the same 1989-04-19 date: US 5,324,844 (divisional, "Active carbonates…"), US 5,612,460, and US 5,808,096 (process claims, "Process for preparing active carbonates…"). I searched for PTAB activity on these as well and found none; that negative is lower-confidence than the ODP result for the '614 itself, and should be re-verified against PTAB E2E before you rely on it.

Estoppel landscape — the operative point. § 315(e)(2) estoppel is irrelevant here: estoppel only attaches to a petitioner after institution, and no IPR was ever instituted. There is no estoppel, but there is also nothing to estop — no petitioner has ever been barred, and no ground has ever been adjudicated. Important structural caveat: IPR/PGR/CBM practice under the AIA did not exist until 2012-09-16, more than three years after this patent expired on 2009-06-16. AIA trials were never available at any time during the patent's enforceable term. PGR is independently unavailable (requires an effective filing date on/after 2013-03-16; this patent's priority date is 1989-04-19), and CBM never applied (not a financial-services patent, and the CBM program sunset on 2020-09-16). So the empty docket is an artifact of timing, not evidence that the claims withstood attack. Do not read the absence of IPRs as a validation signal.

Pattern signals. No repeat petitioner (there are no petitioners). No PTAB appeals by the patent owner (the patent owner, Enzon, did litigate its PEG portfolio in the late 1990s and early 2000s — its 1998 suit against Shearwater Polymers, Inc. and its 2000 suit against Roche, both resolved by the 2001 Schering-Plough/Roche settlement and a January 2002 Shearwater settlement with a $3.0 million payment to Enzon — but those actions concerned Enzon's branched PEG patents, and I found no indication the '614 was the asserted patent; treat that as unconfirmed). No defensive aggregator (Unified Patents, RPX, or similar) appears anywhere in the chain. One item to flag with caution: a June 25, 1998 Enzon private-placement legal opinion, reproduced on Enzon's investor site, states there is "no information which forms a basis for a finding of unenforceability or invalidity of any of the claims of the Patents and Patent Applications except for with regard to U.S. Patent No. 5,324,614; prior art uncovered after the '614 patent issued may be deemed to be such information…" The number as printed (5,324,614) does not match US 5,122,614, and I could not confirm it is an Enzon patent; it may be a typographical error in the filing, or a reference to a different patent. I cannot resolve this and do not rely on it — but if a seller or licensor ever asserts this family, the existence of that sentence in the patent owner's own diligence record is worth a targeted follow-up.

Recommended next steps

• If you are a defendant facing an assertion of US 5,122,614: the dispositive defense is not invalidity — it is expiration and the statute of limitations. The patent expired 2009-06-16 (confirmed on the Google Patents record legal-status line, "Anticipated expiration / Expired – Lifetime"). The § 286 six-year damages lookback has long since closed. Lead with that, and demand the plaintiff identify the specific accused acts and their dates. There is no FWD to quote, because none exists.
• Do not commission an IPR. An AIA trial cannot revive a claim that is not being infringed and cannot be infringed. Any IPR filed now would be a spent fee with no estoppel benefit to anyone.
• Verify the negative directly before you certify it to a court or an investment committee. Run the patent number on USPTO PTAB E2E and the USPTO Patent Center (including the reexamination tab — I found no ex parte reexamination record, but reexaminations do not always appear in the ODP AIA-trials endpoint), and search the CourtListener docket database and the Federal Circuit docket for appeals. My searches surfaced no PTAB proceeding, no reexamination, and no CAFC appeal on this patent, but absence of evidence in a web search is not a certified clearance.
• If the assertion is against a later-expiring family member (e.g., a continuation or a reissue-generation patent claiming priority back to the 1989-04-19 filing), the analysis changes completely and the empty PTAB docket for the '614 tells you almost nothing. Re-scope the search to the specific asserted patent number, and check whether the AIA-trial window was open during that patent's enforceable life.

I'll research the assignment record and ownership history before reconstructing the chain.

Let me dig into the specific assignment records and the Enzon asset dispositions.

US 5,122,614 — Assignment & Ownership Reconstruction

Verification sources used: Google Patents legal events (authoritative snapshot supplied in the prompt), USPTO Assignment Center / legacy indexed search, Enzon SEC filings (8-K 2013-04-30, 10-K/10-Q series), Nektar/Inhale merger-era SEC filings, and Unified Patents / RPX asserter records.

Data-quality caveat up front (important): the Google Patents legal-events block I could retrieve records the existence and date of one assignment but does not expose the reel/frame number or the correspondent of record. I could not render the Assignment Center SPAs to pull the raw reel/frame. Every reel/frame field below is therefore flagged as not captured — verify at Assignment Center, rather than invented. This is a real gap in the record I was given, not a finding.

Inventors

• Sole named inventor. The application (Ser. No. 07/511,243, a CIP of Ser. No. 340,928 filed 1989-04-19) was assigned to Enzon, and the inventor's subsequent PEGylation patents (e.g., the divisionals/continuations US 5,324,844, US 5,612,460, US 5,808,096) are all Enzon filings — i.e., Zalipsky was a staff chemist at the assignee, not an independent inventor.
• No "inventor exodus" pattern applies. The classic fire-sale tell (all inventors leaving the original assignee within 12 months of filing) is not present: with a single inventor who remained at Enzon across the entire family, this is a straightforward employee-invention chain.
• Attorney of record during prosecution was John P. White / Craig J. Arnold (per the patent front page, via uspto.report). Note these are prosecution counsel, not the assignment correspondent — do not conflate the two.

Original assignee

• Entity on the issued patent: Enzon, Inc., a New Jersey corporation, South Plainfield, NJ (later reorganized as Enzon Pharmaceuticals, Inc., NASDAQ: ENZN).
• Primary line of business: PEGylation chemistry and PEG-conjugated biopharmaceuticals. Enzon commercialized PEG-modified proteins (Adagen, Oncaspar) and, critically, monetized its PEGylation patent estate as a licensing platform — the SC-PEG/BSC-PEG carbonate chemistry claimed here (claims 1–6, the compound itself) is core to that platform.
• Did they ship a product embodying the claims? The claims are to the activated PEG reagent compound (SC-PEG / BSC-PEG), not to a drug. Enzon's embodies-the-claims artifact is its own reagent platform and the conjugates made with it; Enzon's marketed drugs used earlier-generation PEG chemistry. Treat "ships a product embodying the claims" as partially — reagent/platform yes, consumer drug no.
• Current status: Operating company in run-off, not dissolved. Enzon wound down R&D in 2013, retained only royalty streams, and announced a merger with Viskase on 2025-06-23 (outside date 2026-03-31). No bankruptcy filing is on record. Note the original assignee still exists as a legal entity, so a "dissolved/orphaned patent" narrative does not apply.

Assignment timeline

Only one recorded assignment appears in the source I retrieved. There is no post-issuance assignment chain on this patent in the Google Patents legal-events snapshot:

• Executed date: not captured / recorded 1990-09-14 — Reel not captured — verify at Assignment Center / Frame not captured
  • Conveyance: Assignment of Assignors' Interest (Assignment)
  • Assignor: Shmuel Zalipsky (sole inventor)
  • Assignee: Enzon, Inc., a corporation of New Jersey
  • Correspondent: not exposed in the retrieved record — cannot be reported without fabricating. Verify at Assignment Center.
  • Context: Contemporaneous with filing — inventor-to-employer assignment establishing original title. This is the only USPTO-recorded link in the chain.

Material transactions that implicate this patent but are NOT recorded as assignments to it (flagged as events, not assignment links):

• 2002-01-07 — Enzon / Inhale Therapeutics (Nektar) strategic alliance. Per the parties' filings, Nektar received "the exclusive right to grant sublicenses under Enzon's PEG patents," described as "over 40 US patents." This is a license/sub-license arrangement, not an assignment; whether any recordation was made against this specific patent is unresolved. Enzon also received $3M and the parties settled Enzon v. Shearwater (the 1998 branched-PEG infringement suit).
• 2009-06-16 — Anticipated expiration of US 5,122,614 (listed legal status). The patent term ended before the 2013 transaction below, which materially undercuts any claim that this patent was a live assertion asset post-2009.
• 2013-04-30 — Enzon's asset purchase agreement selling the "Customized PEGylation Linker Technology platform and related assets," "including certain patents," to Belrose Pharma Inc. for a stated aggregate upfront of $800,000. No assignment record for US 5,122,614 to Belrose was found in the sources retrieved, and given the patent had expired in 2009 it is unlikely to have been a transferred asset. Do not assert a Belrose link to this patent without pulling the assignment schedules at Assignment Center.

Identifier caution: an Enzon SEC exhibit in the retrieved results references "U.S. Patent No. 5,324,614" in a patent-rights context. That is a distinct number and must not be conflated with US 5,122,614 (this patent) or US 5,324,844 (the divisional of this family). Identifiers are quoted literally here, per the no-auto-correction rule.

Timeline diagram

timeline
    title Ownership of US 5122614
    1989 : Inventor files parent case
    1990 : CIP application filed
         : Assignment recorded to Enzon Inc
    1992 : Patent issues to Enzon
    2002 : Enzon licenses PEG patents to Nektar
    2009 : Patent term expires
    2013 : Enzon sells PEGylation platform to Belrose

NPE / troll-pattern signals

1. Shell-entity transfer — not present. The single recorded conveyance (recorded 1990-09-14) runs from the inventor to Enzon, Inc., an operating New Jersey corporation. There is no transfer to a naming-suffix LLC (IP / Holdings / Ventures / Licensing), no registered-agent address of record, and no single-purpose entity anywhere in the recorded chain. No reel/frame supports a shell transfer because no such record exists in the retrieved data.

2. Known asserter in the chain — not present. Neither Enzon, Inc. / Enzon Pharmaceuticals, nor Belrose Pharma, nor Nektar Therapeutics appears on the Acacia, Marathon, IV, IPNav, Wi-LAN, Conversant, Vringo, Pendrell, Innovatio, MPHJ, Lumen View, Round Rock, or Spangenberg lists, nor in Unified Patents' / RPX's high-frequency-plaintiff directories I could reach. Caveat worth stating precisely: Enzon was an active patent enforcer in its operating years (it sued Shearwater over branched PEG, resolved 2002). That is operating-company assertion against a competitor, which is the opposite of the NPE signal — do not misread it as troll conduct.

3. Repeat correspondent across the chain — unclear / not determinable. The retrieved record does not expose the assignment correspondent, and there is only one recorded link, so recurrence cannot be tested. This is the one signal I most want verified because it is where NPE families usually leak: run the Assignment Center query and capture the correspondent on the 1990-09-14 entry, then cross-check that attorney against Unified Patents' and RPX's correspondent lists. Reporting a name now would be fabrication.

4. Cascading transfers — not present. One recorded link, no chains of LLCs, no shared correspondent addresses, no sub-24-month succession. Nothing to cascade.

5. Pre-litigation transfer — not present. No assignment is dated within 6 months before any infringement suit naming this patent. The 1990 assignment is contemporaneous with filing, not with litigation; the only relevant litigation (Shearwater, 1998) was brought by the original owner, not a transferee.

6. Bankruptcy fire-sale — not present. Enzon never filed Chapter 7/11. The 2013 Belrose transaction was an orderly wind-down asset sale at a nominal $800K consideration — notable as a de minimis disposal, but it is not a §363 bankruptcy sale, and this expired patent is not shown to be among the sold assets.

7. Privateering — not present / unclear. The 2002 Nektar arrangement granted a sublicensing right to an operating company in a broad cross-license that also settled litigation. That is monetization-by-licensee, not the classic operating-company→NPE proxy-assertion pattern surfaced by Patent Progress/EFF. I would not call this privateering on the evidence available.

8. Defensive aggregator — not present. The chain does not terminate at RPX, AST, LOT Network, Unified Patents, or OIN. No neutralization event of record.

Verdict

Insufficient data — only the original assignment is of record.

Justification: The sole USPTO-recorded conveyance is the 1990-09-14 inventor→Enzon, Inc. assignment (reel/frame not captured — verify at Assignment Center); there is no post-issuance chain, no shell-entity transfer, no known asserter, and no litigation-timed transfer anywhere in the retrieved record. The patent's anticipated expiration on 2009-06-16 means it has been unassertable for over fifteen years, which independently forecloses most NPE-pattern theories even before the missing correspondent data is filled in. The residual uncertainty is narrow and mechanical: confirm the reel/frame and the assignment correspondent on that single 1990 entry, and confirm whether US 5,122,614 appears on any schedule to the 2013-04-30 Enzon→Belrose asset purchase agreement — those two lookups would convert this from Insufficient data to a clean Owner-retained / non-asserting call.

Verify at: https://assignmentcenter.uspto.gov/ (search patent number 5122614) — mirrored at https://assignment.uspto.gov/patent/index.html

I'll verify the patent number and pull details on each cited prior-art reference.

Let me get the exact "Patent Citations" list on the face of US5122614 and verify at USPTO.

Prior-Art Analysis — US 5,122,614

0. Number verification (literal, no auto-correction)

Confirmed: the number 5122614 corresponds to US 5,122,614 A / US5122614A, application US07/511,243, "Active carbonates of polyalkylene oxides for modification of polypeptides," Zalipsky, Enzon, Inc., filed 1990-04-19, granted 1992-06-16. This is the patent text supplied in the research packet and reproduced at https://patents.google.com/patent/US5122614/en.

No different patent bears this number. Hits on the string "5122614" outside the patent literature (e.g., Westlaw reporter cites) are unrelated — consistent with the earlier "no litigation found" section.

Confusable-family warning (flagged, not corrected): the '614 patent's own family members are US 5,324,844 (divisional), US 5,612,460, and US 5,808,096. A secondary EPO citation listing rendered one of these as "US 5324944 A 19940628 – ZALIPSKY SHMUEL" (http://data.epo.org/pise-server/rest/collections/lgpi/EP2279755A2.pdf). That is an apparent typographical corruption of 5,324,844 and is not the '614 patent and not a separate reference. Do not rely on "5,324,944" as a real document without independent verification. Likewise, freepatentsonline citation tables list "5122614 … 1992-06-16 … Zalipsky," which is the '614 patent being cited as prior art by later documents — again, not prior art to '614.

Tool limitation: I could not execute a live authenticated query against USPTO Patent Public Search / PatentCenter; my tooling is general web search, and searches were truncated at the step limit. Verification above rests on the authoritative Google Patents full text (USPTO-derived) plus corroborating secondary records. Where I could not confirm an entry, I say so rather than filling it in.

1. What counts as a "citation" on '614 — three different lists, don't conflate them

One anomaly inside the "Cited By" list worth flagging: JP2875884B2, listed with priority date 1989-04-19 and assignee Novo Nordisk ("Active polyalkylene oxide carbonates for use in modifying polypeptides"). Because its priority date is identical to '614's, it is an apparent same-priority counterpart/relative, not prior art. It should be treated as family, not as a §102 reference.

2. Patent citations (U.S. patent documents) — confirmed

2.1 US 4,179,337 — Davis, Van Es, Palczuk; "Non-immunogenic polypeptides"

Why it does not anticipate. Claim 1 of '614 requires as an integral element a terminal –O–C(=O)–O–R₅ carbonate ester where R₅ is an N-dicarboximide. US 4,179,337 discloses only a generic "activated polymer containing a reactive terminal group" and attributes the immunogenicity benefit to the polymer chain, not to any specific carbonate chemistry. Typical coupling chemistry there is via cyanuric chloride and similar generic activators. Missing element: the N-dicarboximide carbonate. It therefore fails the "arranged as in the claim" test for every claim.

Where it does matter: it is the §103 starting point and the support for the "modified polypeptide" subject matter described (but not claimed) in '614's Summary. It also discloses the alkylene units recited in claim 2 (PEG = –CH₂CH₂–; polypropylene glycol = –CH₂CH(CH₃)–), but disclosure of a subunit is not disclosure of the claim as a whole.

2.2 US 4,670,417 — Iwasaki et al.; "Hemoglobin combined with a poly(alkylene oxide)"

Why it does not anticipate. The '417 patent teaches N-hydroxysuccinimide esters of a poly(alkylene oxide) (i.e., PAO–O–(CH₂)ₙ–CO–O–Su), not N-succinimidyl carbonates (PAO–O–CO–O–Su). The distinguishing element — the interposed –O–C(=O)–O– carbonate — is absent, and the specification of '614 itself identifies this ester linkage's hydrolytic instability as the defect the invention cures (Figs. 1–2). An activated succinimidyl PAO is not the claimed activated succinimidyl PAO carbonate.

Why it is nonetheless the key §103 reference. It supplies (i) poly(alkylene oxide) as the polymer, (ii) N-hydroxysuccinimide as the activating/leaving group, and (iii) expressly names N-hydroxyphthalimide — i.e., two of the R₅/R₁ imides recited in claims 3 and 4 — for a polyalkylene oxide. The remaining question on claims 1/3/4 is whether swapping the succinate ester for a carbonate linkage (and the corresponding leaving-group choice) would have been obvious.

2.3 Unverified third entry

Aggregator "Patent Citations (3)" implies one further patent-document reference beyond 2.1 and 2.2. I could not verify its identity and will not guess. Candidate-frequency reasoning (e.g., Pierce Chemical's US 4,002,531 or analogous early "activated PEG" documents appearing in sibling-family citation tables) is speculation only and is expressly not offered as a finding. Anyone needing the complete face-of-patent list should pull the USPTO PatentCenter "References Cited" / PTAB-equivalent bibliographic data for application 07/511,243 directly.

3. Non-patent literature cited in the '614 specification (authoritative text)

4. Additional references of record in the sibling process patent US 5,808,096 (same family)

PubChem's record for US-5808096-A (https://pubchem.ncbi.nlm.nih.gov/patent/US-5808096-A) lists the following as cited references. They are the search results the Office appears to have considered against the process claims of the continuation, and they bear on the '614 compound only indirectly:

5. Bottom line — per-claim §102 assessment

No cited reference, alone, anticipates any of claims 1–6 of US 5,122,614. Every one of them fails at least one express claim element:

Where the real risk lies is §103, not §102. The obviousness case the applicant had to answer is the combination of:
(a) a succinimidyl-activated poly(alkylene oxide) (US 4,670,417; Abuchowski 1984); plus
(b) a known hydroxyl-activation reagent giving a succinimidyl carbonate (Ogura 1979 / Wilchek 1985); or
(c) a known PEG carbonate that forms urethane-linked conjugates (Veronese 1985; Beauchamp 1983).

The applicant's rebuttal, grounded in the specification's own experimental data, is the K_am/K_h selectivity ratio (Table 1: e.g., at pH 7.8/27 °C, SC-PEG = 12.6 vs SS-PEG = 7.0), the superior storage stability (Fig. 2), the broader usable pH range (Fig. 3, optimum ≈ pH 9.3), and the greater conjugate stability (Fig. 1, urethane vs. ester). Those are unexpected-property and teaching-away arguments against the (a)+(b)/(c) combination — they do not, however, convert any single reference into an anticipatory one.

6. Caveats and flagged inconsistencies

1. Third face-of-patent citation unverified. "Patent Citations (3)" is reported by an aggregator only; the authoritative packet lacked the backward-citation table. The two U.S. patents I can ground are US 4,179,337 and US 4,670,417, both from the specification text itself. Anything beyond these two is stated as unverified.
2. Date-string discrepancy (flagged, not corrected): US 4,179,337 is given as 1979-12-18 by Espacenet and as 1979-12-01 by patents.searchlight.law. I have used 1979-12-18.
3. Apparent typo in a secondary source: "US 5324944 A 19940628 – ZALIPSKY SHMUEL" almost certainly denotes US 5,324,844, a family member of '614 — not a distinct reference. Flagged, not silently corrected.
4. JP2875884B2 shares the 1989-04-19 priority and is therefore family, not prior art, notwithstanding its appearance in the forward-citation list.
5. No "similar number" hits. I did not locate any other patent bearing 5122614; the numeric collisions found were non-patent citations.
6. Meeting-date inconsistency: the task header states "Current Date: April 26, 2026," whereas the operating environment states 2026-09-28. This does not affect any substantive conclusion above (all dates of record are 1973–1992), but it is flagged per the cross-reference instruction.

I'll ground a few key facts about the cited prior art before building the § 103 analysis.

Let me check whether this patent was ever challenged, and confirm a couple of key reference details.

Obviousness Analysis — U.S. Patent 5,122,614 (Zalipsky, Enzon)

Analysis under pre-AIA 35 U.S.C. § 103(a) (the '614 application was filed 1990-04-19 and claims priority to 1989-04-19; the AIA § 103 framework does not apply). Graham v. John Deere Co., 383 U.S. 1 (1966); KSR Int'l Co. v. Teleflex Inc., 550 U.S. 398 (2007).

0. Preliminary caveats (read before the analysis)

1. Date discrepancy. The task header states "Current Date: April 26, 2026," while the research packet's fetch stamp and my operating date are 2026-09-28. This does not affect the § 103 analysis (critical date is 1989/1990), but the inconsistency is flagged rather than silently normalized.
2. Source of the "Prior Art" set. The authoritative Google Patents text supplied in the packet contains (a) the examiner's Prior art keywords ("peg / sup / sub / protein / modification"), (b) a Cited By (363) table, and (c) the references quoted inside the specification's Background. The patent's front-page "References Cited" list is not in the authoritative text; the list I use below (Davis '337, Batz '786, Barcelo '430, Matsuda CA 111:112046m, Abuchowski 1984) comes from a secondary reproduction (everypatent.com). Treat that list as unverified against the official copy.
3. The strongest single reference I found (Ogura/DSC) is not in the patent's own cited-art list. I flag it separately in § 4 as a candidate that a challenger would be expected to raise.
4. I have not verified the actual disclosures of US 4,248,786 (Batz) or US 4,891,430 (Barcelo) — both are classified in heterocyclic/succinimide chemistry (260/326.26 and 548/542 respectively), which makes them potentially material. This is the largest evidentiary gap in the analysis.

1. Person having ordinary skill in the art (PHOSITA)

A polymer/bioconjugate chemist with a Ph.D. (or M.S. plus several years) in organic chemistry, biochemistry, or polymer chemistry, with practical experience (i) activating poly(alkylene oxide)s at their hydroxyl termini, (ii) reacting activated polymers with protein amine groups in aqueous buffer, and (iii) using N-hydroxysuccinimide ("NHS"/"HOSu") active esters and chloroformate/carbonate chemistry. This level of skill is established on the face of the record itself: the '614 Background is written as a survey of the known activation toolbox (cyanuric chloride, SS-PEG, carbonyldiimidazole, phenyl chloroformates), which presupposes that this toolbox was routine knowledge.

2. Claim 1 deconstructed — and what the prior art must supply

Claim 1 (the only independent claim) covers:

Structurally, claim 1 is the intersection of two known reagent families: the poly(alkylene oxide) carbonate family (element c skeleton) and the N-hydroxysuccinimidyl-activated PEG family (element c leaving group). That framing drives the entire § 103 case.

3. The prior art set and what each reference contributes

4. Combination 1 (primary): Veronese 1985 + Abuchowski 1984 (SS-PEG) — and/or + Iwasaki '417

This is the combination most likely to invalidate claim 1 (and a fortiori claims 4, 5).

The structural difference is one variable. Veronese's species is PEG–O–CO₂–Ar (Ar = p-nitrophenyl or 2,4,5-trichlorophenyl). Claim 1 covers PEG–O–CO₂–(N-dicarboximide). Both are carbonate esters of the same poly(alkylene oxide) hydroxyl, both acylate protein amines through the same carbonyl, and both produce the same urethane (carbamate) linkage. The chemistry and the product are identical; only the identity of the displaced alcohol (phenol → N-hydroxyimide) changes.

Why a PHOSITA would have been motivated to make that substitution:

1. The problem and its two criteria were expressly recognized in the art. The '614 Background itself recites the field's two requirements (fast mild reactivity; non-toxic/readily separable residues) — and then critiques the prior art as failing exactly one criterion each: Veronese satisfies reactivity but releases toxic, hydrophobic phenol residues (p-nitrophenol / 2,4,5-trichlorophenol) with affinity for proteins; SS-PEG satisfies the residue criterion but has a labile ester. Identifying a problem in the art and the criterion for its solution is the classic predicate for obviousness.
2. The solution was a "finite number of identified, predictable solutions." KSR, 550 U.S. at 421. Given a PEG chloroformate/carbonate core, the leaving group is a single design variable, and the art already enumerated the candidates: imidazole (Beauchamp), aryl/phenol (Veronese, and the later EP 632 082 A1 / DMAP variant), and N-hydroxysuccinimide (Abuchowski; Iwasaki). Later art in this very field describes it in precisely those terms — "converting PEG into a chloroformate … This theme can be played in many variants substituting the chlorine with **N-hydroxy succinimide … with imidazole … with para-nitrophenol, DMAP … All these groups give rise to carbamate linkages to the peptide" (US 6,245,901 description). That passage is post-dating and not prior art, but it is evidence of how ordinary this mapping was to the skilled artisan.
3. NHS was the known, non-toxic answer. Abuchowski 1984 and Iwasaki '417 both put NHS on the end of an activated PEG and both taught that (i) NHS esters react with protein amines in ~30 min in mild aqueous buffer, and (ii) the released N-hydroxysuccinimide is non-toxic and used routinely in protein chemistry — the patent itself concedes this. Replacing phenol with NHS therefore directly satisfies the second criterion that Veronese failed, without sacrificing the first.
4. The 1-carbonyl "carbonate" core was independently known to be the fix for the ester-lability problem. Beauchamp (PEG-imidazolyl carbonate), Veronese (PEG-phenyl carbonate) and Larwood & Szoka (urethane stability) collectively teach that a PEG carbonate → urethane route avoids the labile ester, while Berger & Pizzo teach the urethane conjugate is better, not merely more stable.
5. No teaching away. Nothing in Veronese, Abuchowski, Iwasaki, Beauchamp or Ulbrich disparages a succinimidyl carbonate, or teaches that N-hydroxyimides are unsuitable as carbonate leaving groups. The prior art's own criticism is directed at the phenol residues, which cuts in favor of the substitution.

Reasonable expectation of success. The transformation is textbook, and the '614 specification confirms it was routine: PEG chloroformate is generated in situ by treating the polymer with phosgene, then reacted with HOSu and triethylamine (Scheme 3 and Examples 1–2), with essentially quantitative active-carbonate content (Example 1: "101% of theoretical"; Example 2: "98%"). No undue experimentation is needed to arrive at the claimed compound starting from the combination.

Verdict — Combination 1: Strong prima facie case of obviousness of claim 1 as a whole, and of claims 4 and 5 (which merely narrow to N-succinimide and to the mPEG/H-capped species that Veronese and Abuchowski both used). Strength: high, contingent on confirming that Veronese's disclosure is as its abstract reports and that no reference teaches away.

5. Combination 2: Veronese 1985 + Beauchamp 1983 (leaving-group optimization)

Beauchamp teaches a PEG carbonate (imidazolyl) that forms urethane links with lysine ε-amines — i.e., the claimed carbonate-to-urethane concept — but with a weak leaving group, necessitating 48–72 h at pH 8.5. A PHOSITA seeking to keep the urethane chemistry while shortening reaction time to the ~30 min benchmark already established for NHS-activated PEGs (Abuchowski) would substitute the imidazole/phenol leaving group for the higher-utility N-hydroxyimide leaving group. The '614 specification itself frames the invention as exactly this trade-off ("reactivity of the new agents, SC-PEG and BSC-PEG, are comparable to the conventionally used SS-PEG… higher degrees of modification achievable in shorter periods of time" versus CDI-PEG). Strength: high — this is a pure, well-motivated leaving-group optimization, and the art supplies the success benchmark.

6. Combination 3: DSC (Ogura et al., 1979) + Davis '337 — the reference the record omits

N,N'-disuccinimidyl carbonate ("DSC") was first synthesized by Ogura et al. in 1979 and is the standard reagent for converting hydroxyl groups into N-succinimidyl carbonates, which then react with amines to give carbamates (protocol literature: "NHS Carbonate Activation of Hydroxylic Supports using DSC"; "Primary and hindered secondary alcohols (to form carbamates with amines)" — yield 65–89%). Applying a known hydroxyl-activating reagent to a known class of hydroxyl-terminated polymers used for protein conjugation (Davis '337; Veronese; Abuchowski; Beauchamp) is the paradigm of obviousness: a known reagent applied to a known substrate for its known purpose.

Two important qualifications:

• I retrieved this from secondary/aggregator sources (a BenchChem technical guide dated Dec 2025 citing Ogura et al.; ScienceDirect topic pages). The 1979 Ogura primary reference has not been verified, and I could not confirm whether it discloses applying DSC to poly(alkylene oxide)s. If it does, claim 1 may additionally be vulnerable under § 102.
• DSC is not in the '614 front-page citation list as reproduced. Its omission would be a notable gap if it is as broad as the secondary sources indicate.

Verdict: Potentially the most efficient attack on claims 1, 5 and 6, but flagged as unverified and should not be relied on without pulling the primary literature.

7. Combination 4: PEG chloroformate + HOSu (process/method-of-making framing)

The claimed compounds are the direct product of reacting a poly(alkylene oxide) chloroformate with an N-hydroxydicarboximide in the presence of a base — the very process recited in the patent's Summary and Scheme 3. Both halves are known: PEG chloroformate from phosgene + PEG (the specification treats this as an in-situ, one-pot step needing no elaboration), and chloroformate + N-hydroxyimide → activated carbonate (the standard "substitute the chlorine with the desired leaving group" transformation, as later art in this field describes it). Where a claim to a compound reads on the sole, predictable product of a known reaction between known reactants, the claim is obvious as a product of an obvious process. Strength: moderate-to-high, useful as a secondary theory supporting Combination 1.

8. Dependent claims 2, 3, 5, 6

9. Anticipated rebuttals and secondary considerations

(a) "Unexpected" hydrolytic stability of the conjugate. The patent's FIG. 1 shows SC-PEG-derived PEG-BSA is more stable than SS-PEG-derived conjugate. This is not unexpected — it was expressly taught or predicted by Veronese 1985 (urethane route), Beauchamp 1983, and Larwood & Szoka 1984, and the Background recites all three. No nexus.

(b) "Unexpected" selectivity and storage stability of the reagent. Table 1 shows SC-PEG is less reactive than SS-PEG (K_h 10.3 vs. 21.6 ×10⁻³ min⁻¹ at pH 7.8/27 °C) but with a more favorable selectivity ratio (K_am/K_h 12.6 vs. 7.0 at pH 7.8/27 °C) and better storage stability (FIG. 2). These are real advantages, but they are modest in magnitude (well under a factor of two on the selectivity ratio at most pH/temperature conditions in Table 1) and are the predictable consequence of replacing a labile succinate ester with a carbonate while retaining NHS. A patentee would need to show the advantages are unexpectedly large or that the prior art taught the opposite direction — the data in Table 1 shows SC-PEG is slower, which is the "wrong" direction for a reagent the art valued for fast reaction (Veronese: "rapidly at pH near neutrality").

(c) Teaching away. I found no teaching away. The references criticize phenol leaving groups, not imide leaving groups. An argument that a PHOSITA would have expected a succinimidyl carbonate to be too hydrolysis-labile does not work on this record: the patent's own Table 1 shows SC-PEG is more hydrolysis-resistant than SS-PEG, so the alleged prejudice is contradicted by the inventor's data and was not a documented prejudice in the art.

(d) Commercial success / licensing. Likely weak on nexus. The 1990s Enzon PEG-enzyme products that are commonly associated with this era (e.g., PEG-adenosine deaminase) are generally described in the literature as using the earlier succinimidyl-succinate/carbonate chemistries, and I could not verify that any blockbuster product practiced the '614 claims. Unverified — do not assert.

(e) Prosecution history. The examiner allowed over Davis '337, Batz '786, Barcelo '430, Matsuda CA 111:112046m, and Abuchowski 1984 (per the secondary reproduction). That is evidence the examiner did not find this particular combination, but it is not a defense: a challenger's burden is to show what the references teach, and the Veronese 1985 combination does not appear in the reproduced reference list at all, despite Veronese being discussed at length in the specification's Background as prior art.

(f) § 112 backstops (outside § 103). Claim 1's genus sweeps in poly(propylene oxide), poly(butylene oxide), block/random copolymers, and any N-dicarboximide, with a = 1–1000 — yet the specification exemplifies only PEG and (nominally) the imide variants. A written-description/enablement attack on the full genus is available and would narrow the claims toward the exemplified species, which are the ones most plainly obvious.

10. Bottom line and confidence

Combinations that would render the claims obvious:

1. Veronese 1985 + Abuchowski 1984 (SS-PEG) (optionally + Iwasaki '417 and/or Larwood & Szoka 1984) → claims 1, 4, 5 (and, with Davis '337, the genus). Strongest theory. Motivation: recognized two-criteria problem; substitution of the toxic phenol leaving group with the known non-toxic NHS leaving group while retaining the carbonate core that yields the known-stable urethane.
2. Veronese 1985 + Beauchamp 1983 → claims 1, 4, 5 via leaving-group optimization of a known PEG carbonate.
3. DSC (Ogura 1979) + Davis '337 (and/or Veronese) → claims 1, 5, 6; potentially § 102 as well. Unverified — highest-priority pull.
4. Chloroformate + N-hydroxyimide process knowledge → supports all compound claims as products of an obvious, conventional one-pot process.
5. Dependent claims 2, 3, 6 fall with the independent claim by routine class-member selection and known polyalkylene oxide / homobifunctional chemistry.

Confidence:

• High that claim 1–6 face a strong prima facie § 103 case over Veronese + Abuchowski/Iwasaki — the difference is a single, well-motivated leaving-group substitution within one known reagent family.
• Moderate as to whether that prima facie case would survive a well-supported Rule 132 showing of unexpected results; on the present data the selectivity/stability margins are small and the stability advantage was already in the art.
• Low/unverified as to US 4,248,786 (Batz), US 4,891,430 (Barcelo), Matsuda CA 111:112046m, and the primary Ogura 1979 DSC disclosure. These four should be obtained and read in full before any conclusion is finalized; the front-page reference list I used is from a secondary reproduction, not the authoritative text.

Flagged inconsistency with prior sections: the earlier "Patent summary" states the granted claim set contains "neither" a process claim nor a modified-polypeptide claim — that remains accurate, and the § 103 analysis above is confined to the six granted compound claims. No contradiction found between the prior sections and this analysis.