1-Met(S)-Tetrahydropyridazine-1,2,3-Tricarboxylic Acid 1,2-Di-Tert-Butyl Esterhylpyrrole-2-Acetic Acid

Storage and handling protocols for the title compound define its primary commercial utility. The substance is custom-manufactured under ISO 9001:2015 with a certificate of analysis that includes 1H NMR (Bruker 600 MHz, DMSO‑d₆), HRMS (ESI‑TOF, mass error < 3 ppm), and quantitative 13C NMR with internal 1,4‑dioxane standard. Prior to shipment, the material is aliquoted under argon into amber HDPE bottles with tamper‑evident closures, placed in vacuum‑sealed aluminium laminate pouches together with molecular sieve desiccant, and shipped with validated cool packs. A dedicated stability programme conforms to ICH Q1A(R2): samples stored at ‑20 °C and 2–8 °C retain enantiomeric excess above 99.4% over 24 months, while exposure to ambient humidity at 25 °C/60% RH for 72 h results in measurable hydrolysis of the tert‑butyl ester and pyrrole‑acetic acid disproportionation. This foundation of characterisation data makes the material indispensable as a chromatography reference marker for process analytical technology (PAT) deployment in Good Manufacturing Practice (GMP) suites. A 1.0 mg/mL stock in acetonitrile is used to spike reaction monitoring samples; the retention time on a Waters XBridge C18 column (4.6 × 150 mm, 3.5 µm) is 7.82 min under a linear gradient of 0.1% trifluoroacetic acid in water/acetonitrile at 1.0 mL/min. Method qualification per ICH Q2(R1) demonstrates a limit of detection of 0.015 µg/mL and a quantitation limit of 0.050 µg/mL, enabling low‑level impurity tracking in late‑stage synthetic campaigns where residual of the Boc‑protected intermediate must fall below 0.10% area in the final active pharmaceutical ingredient.

Scaling a Temperature‑Sensitive Chiral Intermediate for a Metabolic Disorder Drug Candidate

When medicinal chemistry programmes require a conformationally constrained tetrahydropyridazine core carrying a pendant pyrrole‑2‑acetamide pharmacophore, the tert‑butyl‑protected tricarboxylic acid serves as the strategic gateway. Its primary deployment is in the kilogram‑scale synthesis of a dipeptidyl peptidase‑4 (DPP‑4) inhibitor analogue for type‑2 diabetes research. The process sequence exploits the orthogonal protection: both tert‑butyl esters are cleaved in a single operation to liberate a 1‑methyl‑(S)‑tetrahydropyridazine‑1,2,3‑tricarboxylate intermediate, which is immediately activated and coupled with 2‑(1H‑pyrrol‑2‑yl)ethanamine under amide bond‑forming conditions. The terminal product is a chiral pyrrole‑tethered tetrahydropyridazine‑3‑carboxamide, typically isolated as a crystalline hydrochloride salt with a melting point of 218–222 °C (decomposition). Selection of the deprotection reagent is critical: neat trifluoroacetic acid generates racemisation levels above 12% at room temperature within 15 min, attributed to transient oxonium ion formation at the N‑methyl tertiary amine. A factorial design of experiments (DoE) identified hydrogen chloride in 1,4‑dioxane (4 M) as the optimal system. In a 20 L jacketed Hastelloy reactor equipped with a retreat‑curve impeller and a Pt100 temperature probe, a precooled (‑10 °C) solution of the substrate (1.0 mol, ca. 430 g) in anhydrous dichloromethane is treated with HCl‑dioxane (4.0 equiv, 1.0 L) added via peristaltic pump at 0.4 equiv/h. Internal temperature is maintained at ‑5 to 0 °C by a Lauda Integral T‑1500 circulator using Syltherm XLT fluid, with a tolerance of ±1.5 °C. Real‑time ReactIR monitoring (Mettler‑Toledo iC‑FBRM‑G400) tracks the collapse of the tert‑butyl ester C=O stretch at 1732 cm⁻¹; the endpoint is reached when the peak intensity drops below 5% of the initial value. The quench is performed by transferring the mixture onto a vigorously stirred pre‑cooled aqueous potassium carbonate solution, controlling the pH at 3.5–3.8 during the isoelectric precipitation of the tricarboxylic acid intermediate. Filtration through an agitated nutsche filter, displacement washing with iced water, and vacuum drying at 30 °C yield a white solid with an enantiomeric excess of 99.6–99.9% as determined by supercritical fluid chromatography (Waters UPC², Chiralpak AD‑H, 40% methanol co‑solvent, 3.0 mL/min, 200 bar). The isolated triacid is immediately dissolved in N,N‑dimethylformamide and treated with 1.05 equiv of TBTU and 3.0 equiv of N,N‑diisopropylethylamine at 0–5 °C, followed by the amine partner, to suppress epimerisation. This convergent route has been validated at 5 kg batch scale with an overall isolated yield of 72–78% over three stages, meeting an internal residual palladium limit of < 10 ppm and residual solvent levels compliant with USP <467>.

In asymmetric 1,4‑conjugate additions of arylboronic acids to cyclic enones, a copper‑based catalytic platform built from the deprotected title compound delivers enantioselectivities that compete with bisoxazoline ligands while offering straightforward structural diversification. The operational ligand is formed in situ by treating the fully deprotected tricarboxylic acid (obtained as described above) with 1.0 equiv of copper(II) acetate monohydrate in methanol at 50 °C for 1 h. The resulting deep‑blue complex is precipitated by addition of diethyl ether, isolated under nitrogen, and used directly in catalysis. Bench‑scale reactions are set up in a glovebox (MBraun, O₂ < 1 ppm, H₂O < 0.5 ppm): the pre‑formed Cu‑complex (5 mol% based on copper) is suspended in dry toluene together with 4 Å molecular sieves, the cyclohex‑2‑enone substrate (1.0 mmol), phenylboronic acid (1.5 mmol), and triethylamine (0.5 mmol) as a base activator. Stirring at ‑20 °C for 48 h under argon, followed by filtration through a silica plug and chiral GC analysis (Cyclosil‑B, 0.25 mm × 30 m, isothermal 140 °C), reveals (R)‑3‑phenylcyclohexanone with an ee that typically ranges from 88 to 94% across ten electronically diverse substrates. Published data for this specific configuration is limited to internal feasibility reports, yet structural analogues lacking the pyrrole‑2‑acetic acid arm show a 15–20% drop in ee under identical conditions, suggesting a second‑sphere hydrogen‑bonding role of the distal pyrrole NH. The chiral ketone products are advanced to tetrahydropyridine calcium channel blockers after Baeyer‑Villiger oxidation and Ritter reaction, with no detectable copper carry‑over (< 5 ppb) in the final active by ICP‑MS. Ligand recycling is not effective: attempts to recover the complex by solvent removal led to partial decarboxylation of the pyridazine ring at > 40 °C, so each run employs a freshly prepared batch.

MOF‑808 Analogue Ligands with Pendant Pyrrole‑Carboxylate Coordination

A microporous zirconium‑based metal‑organic framework enters early‑stage material screening when the three carboxyl groups of the fully deprotected compound are positioned as a triangular linker. Synthetic procedure: the triacid (0.5 mmol) and ZrOCl₂·8H₂O (0.5 mmol) are dissolved in 10 mL of anhydrous N,N‑dimethylformamide containing 2.5 mL of formic acid as modulator. The mixture is sealed in a 23 mL Teflon‑lined Parr acid digestion vessel and heated in an isothermal oven at 120 °C for 24 h. After natural cooling, the precipitate is centrifuged, washed with DMF and methanol, and activated under vacuum at 120 °C for 12 h. The resulting microcrystalline powder exhibits a Brunauer–Emmett–Teller surface area of 680–750 m²/g according to ASTM D3663‑20, with a pore diameter centred at 1.2 nm by NLDFT modelling of the 77 K argon adsorption isotherm. Availability of the non‑coordinated pyrrole and tetrahydropyridazine nitrogen sites opens the door to post‑synthetic metalation: immersing the MOF in a solution of palladium(II) acetate in acetone (0.1 M, 24 h) loads 0.8 wt% Pd, as confirmed by inductively coupled plasma optical emission spectroscopy. This Pd@MOF composite catalyses the cycloaddition of CO₂ to propylene oxide at 10 bar and 80 °C, achieving a cyclic carbonate yield of 87% after 6 h with a turnover number of 1040. Because the pyridazine ring is susceptible to ring‑opening at prolonged hydrothermal times above 96 h, the synthesis window must be strictly controlled; extended solvothermal treatment beyond 30 h converts the crystalline phase to an amorphous gel. This instability limits the MOF’s utility to batchwise single‑use heterogeneous catalysis trials.

When the Di‑tert‑butyl Ester is Cleaved Prior to Peptide Coupling in Solid‑Phase Synthesis

Incorporation of a 1‑methyltetrahydropyridazine‑tricarboxyl scaffold into a peptidomimetic requires a precise order of deprotection and coupling. The building block is anchored to Rink amide AM resin (0.47 mmol/g loading) via its C‑3 carboxyl group using standard carbodiimide chemistry. The resin‑bound intermediate is then swollen in dichloromethane, drained, and treated with a freshly prepared mixture of trifluoroacetic acid, triisopropylsilane, and water (95:2.5:2.5, v/v/v, 10 mL per gram of resin) at room temperature for 30 min to cleave both tert‑butyl esters. After thorough washing with CH₂Cl₂ and 5% N,N‑diisopropylethylamine in DMF to neutralise residual TFA, the free carboxylic acids are coupled with an upstream N‑Fmoc‑protected dipeptide. Reagents are used in a molar ratio of 1:1:2 for building block, HBTU, and DiPEA per free acid site (i.e., 2 equiv of HBTU and 4 equiv of DiPEA relative to the resin‑bound scaffold). Coupling is performed in DMF at 25 °C with gentle nitrogen agitation for 2 h; a Kaiser test must be negative before proceeding. The assembled linear peptide‑scaffold conjugate is cleaved from the resin with TFA and purified by preparative reverse‑phase HPLC to give the product as a lyophilised powder. This sequence has been applied to generate a library of 24‑membered macrocyclic protease inhibitors where the pyridazine carboxylic acid acts as a β‑turn mimic. A critical operational boundary must be observed: during Boc removal, any contact between the resin and primary amine bases such as piperidine causes irreversible pyrrole‑2‑acetic acid amidation at the scaffold, evident by an M+H+16 adduct in LC‑MS. Therefore, the deprotection‑neutralisation‑coupling series is conducted exclusively with tertiary amine bases, and post‑cleavage HPLC purity always targets > 95% at 220 nm. Shipping specifications demand −20 °C storage of the intact tert‑butyl ester input material; lots that experience temperature excursions above 40 °C during transit show 2–5% premature de‑esterification and are rejected for solid‑phase use.

Does the Pyrrole‑acetic Acid Moiety Improve Hole‑Transport in Solution‑Processed Polymer Blends?

When the protected ester is used as a molecular dopant in organic photovoltaic bulk heterojunctions, the process begins with ultra‑high‑purity (99.9%) material sublimed under reduced pressure (10⁻⁶ mbar, 150 °C gradient) to eliminate non‑volatile residues. In an argon‑filled glovebox, a solution of P3HT (20 mg/mL in chlorobenzene) is blended with the dopant at loading levels of 0.2, 0.5, 1.0, and 1.5 wt%. Films are spin‑cast onto ITO‑coated glass substrates at 800 rpm for 60 s and thermally annealed on a hot plate at 120 °C for 10 min under nitrogen. Hole‑only devices are fabricated with an architecture of ITO/PEDOT:PSS/active layer/MoO₃/Ag; current‑voltage characteristics are recorded in the dark, and hole mobility is extracted using the Mott–Gurney space‑charge‑limited current model. Doping at 0.5 wt% increases the zero‑field hole mobility from 1.2×10⁻⁴ cm²/V·s to 3.8×10⁻⁴ cm²/V·s, while the 1.5 wt% formulation causes a precipitous drop to 6.0×10⁻⁵ cm²/V·s, interpreted as dopant phase segregation confirmed by atomic force microscopy phase images showing domain clusters of 150–200 nm. The processing window is thus narrow: optimal performance resides at 0.5±0.2 wt% doping. Published data for this specific configuration is limited to one academic preprint, and commercial adoption awaits stable encapsulation strategies that mitigate dopant migration under 85 °C/85% RH accelerated ageing. Its role here is as a high‑value screening additive rather than an off‑the‑shelf component. End users in organic electronics procurement demand a shipment‑release certificate that includes inductively coupled plasma mass spectroscopy for transition metals with a reporting limit of 50 ppb for each element, and Karl Fischer moisture < 50 ppm.

A dedicated application of the title compound lies in the preparation of an impurity reference marker for quality control of a preclinical candidate bearing the tetrahydropyridazine‑pyrrole‑acetic acid motif. When the drug substance is synthesised via a late‑stage amide coupling, the di‑tert‑butyl ester intermediate can carry over as a process impurity if the tert‑butyloxycarbonyl deprotection is incomplete. Using the isolated title compound as a primary standard, a gradient HPLC method is developed: a 4.6 × 100 mm, 2.7 µm fused‑core C18 column (Phenomenex Kinetex) is operated at 40 °C with mobile phase A (water/acetonitrile 95:5 with 0.1% formic acid) and B (acetonitrile/water 95:5 with 0.1% formic acid). The linear gradient from 30% B to 90% B over 12 min resolves the title compound (Rt = 8.34 min) from the des‑tert‑butyl by‑product (Rt = 4.21 min) with a resolution factor > 3.0. A 10 mg vial of the certified reference material, provided with an ISO 17034 accreditation certificate, is dissolved in DMSO‑d₆ for quantitative NMR assay using ethylbenzene as an internal calibrant. The absolute potency is determined to be 98.7 ± 0.5% (k=2). This CRM is shipped within a validated cold‑chain logistics system, and its acceptance criterion for storage upon receipt is immediate transfer to a −20 °C freezer, protected from light by the supplied amber vial sleeve.