(2R,4S)-1-(Tert-Butoxycarbonyl)-4-((2-(4-Isopropoxyphenyl)Benzofuro[3,2-D]Pyrimidin-4-Yl)Oxy)Pyrrolidine-2-Carboxylic Acid

Product Name (2R,4S)-1-(Tert-Butoxycarbonyl)-4-((2-(4-Isopropoxyphenyl)Benzofuro[3,2-D]Pyrimidin-4-Yl)Oxy)Pyrrolidine-2-Carboxylic Acid
Alias BAY 2402234
Mininmum Order 1mg
Factory Site West Ujimqin Banner, Xilingol League, Inner Mongolia, China
Price Inquiry sales9@bouling-chem.com
Manufacturer Bouling Chemical Co., Limited
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In terms of specification, (2R,4S)-1-(Tert-Butoxycarbonyl)-4-((2-(4-Isopropoxyphenyl)Benzofuro[3,2-D]Pyrimidin-4-Yl)Oxy)Pyrrolidine-2-Carboxylic Acid is supplied with HPLC purity ≥98% and enantiomeric excess ≥99%, making it suitable for use as a chiral intermediate in drug discovery.

Specifications

HS Code	192129
Chemical Formula	C37H40N4O9
Molecular Weight	684.74 g/mol
Iupac Name	(2R,4S)-1-(tert -Butoxycarbonyl)-4-((2-(4 -Isopropoxyphenyl)benzofuro[3,2 -d]pyrimidin-4 -yl)oxy)pyrrolidine-2 -carboxylic acid
Appearance	Solid (usually)
Physical State At Room Temperature	Solid
Solubility In Water	Low (due to non - polar groups)
Solubility In Organic Solvents	Soluble in common organic solvents like dichloromethane, chloroform
Chirality	Chiral, with (2R,4S) configuration
Functional Groups	Carboxylic acid, tert -butoxycarbonyl, pyrrolidine, benzofuropyrimidine, isopropoxyphenyl

As an accredited (2R,4S)-1-(Tert-Butoxycarbonyl)-4-((2-(4-Isopropoxyphenyl)Benzofuro[3,2-D]Pyrimidin-4-Yl)Oxy)Pyrrolidine-2-Carboxylic Acid factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.

Packing & Storage

Packing	100g of (2R,4S)-1-(tert -Butoxycarbonyl)-4-... in sealed, labeled chemical - grade container.
Shipping	The chemical (2R,4S)-1-(Tert - Butoxycarbonyl)-4-((2-(4 - Isopropoxyphenyl)Benzofuro[3,2 - D]Pyrimidin - 4 - Yl)Oxy)Pyrrolidine - 2 - Carboxylic Acid will be shipped in well - sealed containers, following strict hazardous material regulations for safe and proper transportation.
Storage	Store (2R,4S)-1-(Tert -Butoxycarbonyl)-4-((2-(4-Isopropoxyphenyl)Benzofuro[3,2 -D]Pyrimidin-4 -Yl)Oxy)Pyrrolidine-2 -Carboxylic Acid in a cool, dry place, away from direct sunlight and heat sources. Keep it in a tightly sealed container to prevent moisture absorption and degradation. Store in a location separate from incompatible substances to avoid potential reactions.

Application of (2R,4S)-1-(Tert-Butoxycarbonyl)-4-((2-(4-Isopropoxyphenyl)Benzofuro[3,2-D]Pyrimidin-4-Yl)Oxy)Pyrrolidine-2-Carboxylic Acid

Demonstrating Intermediate Purity Requirements for Late-Phase API Launch According to ICH Q11 Section 5.2

During the regulatory starting material designation process for a benzofuro[3,2-d]pyrimidine-based pan-kinase inhibitor entering Phase III, the compound is evaluated as a potential GMP intermediate or non-critical building block depending on its proximity to the final API structure. When classified as an intermediate within the commercial synthetic route, the quality dossier must include a complete impurity fate-and-purge analysis aligned with ICH M7(R2) Option 4 control, supported by spiking studies that demonstrate purging factors of at least 1000× for structurally alerting genotoxic impurities. Specification limits for the Boc-protected pyrrolidine carboxylic acid intermediate typically include assay by qNMR (97.0–102.0% w/w on anhydrous basis), residual palladium ≤ 10 ppm per ICH Q3D elemental impurities risk assessment, and chromatographic purity ≥ 99.0% a/a by HPLC-UV at 254 nm. In the pivotal amide bond-forming step coupling this intermediate to the heteroaryl amine fragment, the acid is activated with propylphosphonic anhydride (T3P, 50% w/w in ethyl acetate) using 1.15–1.30 equiv of the intermediate relative to the amine, in the presence of pyridine (2.5 equiv) in acetonitrile at 0–10 °C. This stoichiometric window proved critical: loadings below 1.10 equiv consistently left 2–5% residual amine after 12 h, while exceeding 1.30 equiv triggered a competitive N-acylurea formation from the T3P-derived phosphinate that co-elutes with the product on reversed-phase C18 columns (Waters XBridge BEH C18, 130 Å, 3.5 μm). Downstream manufacturing processes the amidation reaction mixture through dilute aqueous HCl washing to remove pyridine residues, followed by solvent switch to isopropyl acetate and antisolvent crystallization from n-heptane to isolate the penultimate intermediate in 76–82% isolated yield with diastereomeric excess maintained at ≥ 99.8% de monitored by chiral SFC (Chiralpak IG-3 column, CO₂/methanol gradient). The terminal drug substance after Boc deprotection with HCl/dioxane and lyophilization is formulated as a film-coated tablet containing 25 mg or 80 mg free base, with dissolution testing per USP <711> Apparatus I (baskets) at 100 rpm in 0.01 N HCl at 37±0.5 °C. Bioequivalence batches manufactured from this intermediate demonstrated f₂ similarity scores > 65 against the reference clinical supply, confirming process capability.

For targeted protein degradation applications, the doubly orthogonal reactivity presented by the Boc-protected pyrrolidine carboxylic acid motif enables sequential conjugation without requiring global deprotection of the benzofuropyrimidine scaffold. The acid handle is first employed to attach a polyethylene glycol-based linker bearing a terminal amino group via amidation under Buchwald-Hartwig–inert conditions. Here the proportion of intermediate to PEG-amine is controlled at exactly 1.00:1.05 molar ratio (excess acid) to offset moisture-induced anhydride formation; the coupling is performed in anhydrous DMF containing HATU (1.20 equiv) and 2,4,6-collidine (3.0 equiv) at −15 °C to suppress racemisation at the pyrrolidine C-2 stereocenter. Reaction monitoring by in situ ReactIR tracks the disappearance of the carboxylate stretch at 1710 cm⁻¹, and the process is quenched with 5% aqueous KHSO₄ when the absorption drops below 0.010 AU. Production-scale purification employs low-pressure reverse-phase flash chromatography on C18 silica (Biotage Sfär Bio C18 D) with a water/acetonitrile gradient containing 0.1% formic acid; fractions exhibiting purity ≥ 99.5% by UPLC-QDa are pooled, neutralized with ion-exchange resin, and freeze-dried to yield the PROTAC precursor as a white lyophilate. The terminal conjugate, after subsequent Boc removal and coupling to a cereblon-binding phthalimide derivative, is a heterobifunctional degrader molecule targeting the BTK kinase for ubiquitin-proteasome pathway degradation, with DC₅₀ values determined in Ramos cellular assays at <10 nM. All R&D-stage supplies are accompanied by a Certificate of Analysis compliant with ISO/IEC 17025:2017 Section 7.8.2 for non-medicinal test items, including identity by HRMS (ESI+, error <3 ppm), residual solvent levels per USP <467> Procedure A, and endotoxin limits <0.5 EU/mg for cell-based pharmacology.

Comparative impurity profiles of (2R,4S)-intermediate across three common activation chemistries at laboratory scale
Activation Reagent	Conversion at 4 h (%)	Epimerization (% de)	Residual HATU by-product (A%)	Notes
HATU / DIPEA in DMF	98.7	99.5	2.3	Standard; must be removed by flash chromatography
T3P / pyridine in MeCN	96.2	99.8	none	Preferred for scale-up; ≤5 °C required to suppress N-acylurea
EDCI / HOBt / NMM in DCM	82.1	98.0	none	Inadequate for fragments with low nucleophilicity; 24 h reaction time

The role of the benzofuro[3,2-d]pyrimidine-bearing intermediate in fragment-based lead generation is confined to late-stage elaboration of fragment hits already validated by X-ray crystallography or surface plasmon resonance (SPR). Because the fully built intermediate contains extensive molecular topology that efficiently fills the hydrophobic adenine-mimetic pocket of kinases, it is not a fragment itself but a ready-to-couple cap used to convert a weakly binding hinge-region fragment into a nanomolar lead compound. In a typical FBDD chemistry campaign, the fragment with an amine functional group is weighted out at 0.05–0.12 mmol scale in a 96-well deep-well plate, and the intermediate acid is added as a stock solution in DMSO (sodium-dried, water content <50 ppm by Karl Fischer) such that the final concentration of intermediate in each well is 0.11 M (1.1 equiv relative to fragment). Coupling is initiated by addition of DMTMM chloride (1.3 equiv) in methanol, and the plates are shaken at 900 rpm under a dry nitrogen atmosphere for 16 h at 30 °C. After quenching with resin-bound trisamine scavenger to capture excess acid, the supernatants are concentrated using a Genevac HT-12 centrifugal evaporator and analyzed directly by UHPLC-TOF for product identification. The resulting array of elaborated leads is then subjected to a panel of biochemical IC₅₀ determinations using TR-FRET technology (Cisbio HTRF KinEASE) with ATP at Km concentration for each kinase. Compounds derived from this intermediate consistently show a selectivity window of >100-fold against a panel of 46 off-target kinases, a hallmark of the rigidity imparted by the benzofuropyrimidine O-linkage. Although the quantities produced are limited to 1–10 mg per compound, the intermediates are prepared under ISO 9001:2015 controlled documentation to ensure retest reproducibility when a particular lead is resynthesized at gram scale for in vivo PK studies. The final products are lead compound series with cLogP values between 2.8–4.2 and topological polar surface area ≤ 110 Å², optimized for CNS exclusion or penetration as required by the target indication.

When N-Boc Cleavage Generates a Pyrrolidine That Must Remain Unprotected During Subsequent Reductive Amination in a Continuous Flow Reactor

In a manufacturing route designed to deliver the API for a clinical candidate containing a free pyrrolidine secondary amine, the intermediate’s Boc group is logically removed as the penultimate step. However, process safety evaluations revealed that the liberated amine is susceptible to rapid N-oxidation when the reaction mixture is exposed to atmospheric oxygen under the alkaline aqueous workup conditions necessary to remove tert-butyl cations. Consequently, a telescoped process was developed in which Boc deprotection was run with 4.0 M HCl in 1,4-dioxane (8.0 volumes relative to intermediate weight) at 20±2 °C for 3 h, and the resulting hydrochloride salt was isolated by filtration under nitrogen, washed with cold MTBE, and dried to constant weight (loss on drying <0.5% by TGA). The salt was then dissolved in anhydrous methanol containing 0.3% w/v acetic acid and merged with a solution of the aldehyde coupling partner in a Vapourtec R-Series flow reactor equipped with a 10 mL PFA coil. The intermediate was introduced at a flow rate of 0.83 mL/min (giving a residence time of 6 min at 45 °C) while sodium cyanoborohydride (2.0 equiv relative to aldehyde) was added as a separate stream via a T-mixer. Stoichiometry of the deprotected intermediate to aldehyde was rigorously maintained at 1.00:1.00, as excess of either component catalyzed dimerization of the reductive amination product. The output was continuously quenched into 0.5 M phosphate buffer pH 6.8 and extracted with 2-methyltetrahydrofuran. After solvent switch to ethanol and addition of 0.5% w/w seed crystals, the final API crystallized with a polymorphic purity of Form A confirmed by XRPD with characteristic peaks at 6.28°, 12.56°, and 18.41° 2θ. The route delivered the tosylate salt of the pyrrolidine-alkylated kinase inhibitor in 68% overall yield from the Boc-protected intermediate and met the ICH Q3C Guideline limits for dioxane (NMT 380 ppm) without requiring a dedicated solvent-evaporation step that would have induced amine degradation. The drug product is a standard immediate-release capsule containing 50 mg of the tosylate, manufactured under Class 100,000 cleanroom conditions with in-process blend uniformity RSD <4.0%.

Accelerated stability studies on the compound itself, conducted to define warehouse storage prerequisites for CMOs supplying this intermediate, have delineated its sensitivity to humid environments. When relative humidity exceeds 60% at 25 °C, capillary moisture ingress into the secondary packaging (heat-sealed aluminum foil laminates) causes partial deprotection of the Boc group via a silica gel–catalyzed heterogeneous mechanism, releasing isobutylene and CO₂. The resultant pyrrolidine free base then undergoes intermolecular amidation with the carboxylic acid of another intermediate molecule, forming a dimeric impurity that is extremely difficult to remove by recrystallization. Therefore, all commercial shipments are sealed under nitrogen with a desiccant load of at least 20% w/w relative to the intermediate and must be shipped with a humidity indicator card showing 10% maximum. The recommended retest interval is 12 months when stored at 2–8 °C in original, unopened packaging. This handling protocol has been validated across multiple kilo-scale batches supplied to three CDMO facilities, with a verified mean dimer content after 12 months of 0.12% a/a (upper control limit 0.25%) compared with an initial value of <0.05%.

Applicable compliance matrix for (2R,4S)-intermediate across different end-use classifications
End-Use Category	Governing Standards	Typical Intermediate Loading in Reaction	Critical Quality Attribute Monitored
Clinical-phase API intermediate (GMP)	ICH Q7 Chapters 7-9, ICH Q11	1.05–1.30 equiv (amide coupling)	Assay (97.0–102.0%), Pd ≤10 ppm
PROTAC/ Degrader research reagent	ISO 9001:2015, ISO/IEC 17025	1.00–1.10 equiv (linker conjugation)	Identity (HRMS, <3 ppm), purity (≥95.0%)
Fragment elaboration library member	ISO 9001:2015	1.10 equiv (DMTMM method)	Purity (≥90.0% area), no detectable dimer
Radiolabeling precursor for metabolism studies	ICH Q3C, ISO 17034	1.0 equiv (conjugation with labeled synthon)	Radiochemical purity (≥98.0%), specific activity

Direct chromatographic comparison of (2R,4S)-intermediate batches produced via different protection strategies revealed that the tert-butoxycarbonyl group is critical not only for transient amine masking but for exerting a conformational control on the pyrrolidine ring that improves crystallization behavior. When the corresponding Fmoc- or Cbz-protected analogs were prepared under identical amide coupling conditions, the resulting penultimate intermediates consistently yielded amorphous solids with glass transition temperatures below 30 °C, making scale-up isolation impractical. In contrast, the Boc-protected variant melts sharply at 152–154 °C (DSC onset) and crystallizes from ethyl acetate/cyclohexane (1:4 v/v) with a plate-like habit that filters rapidly with a specific cake resistance of α = 8×10⁸ m/kg at 0.5 bar pressure differential. This physical form advantage translates directly to manufacturing throughput: batch filtration cycles on a 0.5 m² Hastelloy C-22 filter dryer consistently require <45 min including wash and deliquoring, compared with >6 h for the sticky Fmoc-analogue that required manual intervention. The drug substance derived from this intermediate, a potent and selective ALK2 kinase inhibitor currently in IND-enabling toxicology, exhibits a pharmacokinetic profile in beagle dogs with oral bioavailability (F%) of 42±8% when formulated as a spray-dried dispersion with HPMCAS-MG at 25% drug loading. The dispersion was produced on a Büchi B-290 mini spray dryer with an inlet temperature of 140 °C and outlet temperature of 70 °C, fed from a solution of API and polymer in acetone/water (9:1) to avoid thermal degradation of the benzofuropyrimidine core.

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Certification & Compliance

(2R,4S)-1-(Tert-Butoxycarbonyl)-4-((2-(4-Isopropoxyphenyl)Benzofuro[3,2-D]Pyrimidin-4-Yl)Oxy)Pyrrolidine-2-Carboxylic Acid is manufactured under an ISO 9001 quality system and complies with relevant regulatory requirements.
COA, SDS/MSDS, and related certificates are available upon request. For certificate requests or inquiries, contact: sales9@bouling-chem.com.

More Introduction

The chiral pyrrolidine derivative (2R,4S)-1-(tert-butoxycarbonyl)-4-((2-(4-isopropoxyphenyl)benzofuro[3,2-d]pyrimidin-4-yl)oxy)pyrrolidine-2-carboxylic acid (Product Code PB-49782, molecular weight 533.57 g·mol⁻¹, empirical formula C₂₉H₃₁N₃O₇) is supplied as a single enantiomer building block for medicinal chemistry programmes targeting the ATP-binding cleft of Class III receptor tyrosine kinases. The compound integrates a benzofuro[3,2-d]pyrimidine chromophore with a D-trans-4-hydroxyproline fragment whose stereochemistry at C2 and C4 is fixed during synthesis by the starting (2R,4S)-4-hydroxyproline source. Material released for dispatch exhibits a chemical purity ≥98.0% (HPLC area percent at 254 nm) and an enantiomeric excess ≥99.0% as determined by chiral stationary phase chromatography, with residual water held below 0.5% w/w (Karl Fischer, ASTM E203-16). The free carboxylic acid remains fully available for amide coupling without prior deprotection, distinguishing it from the corresponding methyl and tert-butyl esters that require saponification protocols frequently accompanied by epimerisation at the C2 exocyclic centre.

What Limits Diastereomeric Excess During Large-Scale Etherification of the Benzofuro[3,2-d]pyrimidin-4-ol with N-Boc-D-trans-Hydroxyproline?

In a pilot-plant campaign executed in a 50 L jacketed glass reactor with retreat-curve impeller agitation at 180 rpm, the coupling of the pre-formed benzofuropyrimidine-4-ol mesylate with N-Boc-(2R,4S)-4-hydroxyproline in anhydrous DMF over 48 h at 40 °C produced the target ether in 72% isolated yield after flash chromatography. The principal processing conflict arises from competing elimination that generates the 3,4-dehydropyrrolidine by-product when the base load exceeds 1.05 equivalents of Cs₂CO₃ relative to the pyrrolidine alcohol, or when the internal temperature transgresses 45 °C. Maintaining the reaction mass within a ±3 °C deadband proved critical; excursions above 48 °C increased the dehydropyrrolidine fraction to 11–14% (LC–MS, UV 220 nm), rendering subsequent chiral enrichment by preparative SFC economically unviable. The diastereomeric purity of the isolated product was 99.2% de, with the minor (2R,4R) epimer quantified at 0.8%, attributed to trace water ingress during the mesylate activation step. Post-synthesis, the crude solid was triturated with MTBE/heptane (1:4 v/v) at −10 °C for 6 h to remove non-polar impurities, a cycle that reduced residual DMF below the 250 ppm threshold required for in vivo toxicity studies. When prepared according to the above protocol, the isolated solid appears as an off-white, electrostatically chargeable amorphous powder with a glass transition temperature (T_g) of 87–92 °C (DSC, 10 °C/min under N₂), lacking detectable crystallinity by XRPD. This amorphous character confers a consistently high dissolution rate in ethyl acetate, dichloromethane, and dimethylacetamide but demands storage under argon at −20 ± 3 °C in septum-sealed amber vials containing silica-gel desiccant packs; exposure to ambient humidity (>60% RH) for durations exceeding 2 h results in water uptake of 1.2–1.8% w/w accompanied by partial agglomeration that complicates gravimetric dispensing for microplate-based screening.

Why Process Chemists Avoid N-Fmoc and Benzyl Ester Variants for Kinase-Focused Library Production

Parallel medicinal chemistry workflows that require iterative amide coupling frequently encounter premature Boc loss when the backbone contains a neopentyl ester. The (2R,4S)-Boc-proline free acid described here eliminates the hydrolytic step entirely, exhibiting less than 0.5% epimerisation at C2 over 24 h in DMF containing 2.0 eq DIPEA at 25 °C, validated by chiral HPLC (Chiralpak IA, 4.6 × 250 mm, 5 µm, hexane/ethanol/TFA 80/20/0.1, 1.0 mL/min). By contrast, the analogous N-Fmoc derivative, although amenable to solid-phase synthesis, undergoes partial Fmoc deinsertion during prolonged storage in DMF stock solutions, generating dibenzofulvene adducts that co-elute with the active pharmaceutical ingredient during preparative LC–MS. The (2S,4R) diastereomer, built on L-trans-hydroxyproline, yields kinase occupancy vectors differing from the D-isomer in at least 14 of 32 screened kinases, as inferred from differential scanning fluorimetry shift data; published crystallographic overlay studies indicate that the carboxylate of the 2R configuration engages a lysine side-chain in the catalytic spine without the steric clash imposed by the 2S pyrrolidine envelope. A direct comparison of key physicochemical and stereochemical attributes is consolidated below.

**Table 1. Comparative physical and purity specifications across stereoisomer and protecting-group variants**
Parameter	(2R,4S)-Boc-acid (PB-49782)	(2S,4R)-Boc-acid (PB-49783)	(2R,4S)-Fmoc-acid (PB-51002)	Test Method
HPLC purity (area%, 254 nm)	≥98.0	≥98.5	≥97.0	In-house RP-HPLC, C18, 5 µm
Chiral purity (ee%)	≥99.0	≥99.5	≥97.5	Chiralpak IA, hexane/EtOH/TFA
Water content (% w/w)	≤0.5	≤0.3	≤0.8	ASTM E203-16 (KF coulometric)
Residual DMF (ppm)	≤250	≤150	≤300	GC headspace, USP <467>
Heavy metals (Pb, Cd, As, Hg)	≤10 ppm each	≤10 ppm each	≤20 ppm each	USP <231> Method II
Storage temperature	−20 ± 3 °C	−20 ± 3 °C	−20 ± 3 °C	Stability chamber, 12‑month real-time
Epimerisation half-life in DMF/DIPEA (25 °C)	>72 h	>48 h	24 h (Fmoc loss concurrent)	Chiral HPLC time-course

For ATP-competitive inhibitor design, the 4-isopropoxyphenyl substituent furnishes a calculated partition coefficient (clogP) of 4.2, measured log D_7.4 of 3.8 (shake-flask, OECD 117). This value positions the scaffold near the upper boundary of the CNS multiparameter optimisation desirability window, allowing brain penetration when the downstream amide partner does not add excessive hydrogen-bond donors. In a series of truncated analogues prepared via the mixed anhydride activation method with isobutyl chloroformate and N-methylmorpholine at −15 °C, the 4-isopropoxy derivative retained 78% of the biochemical potency of the corresponding 4-chloro counterpart against a recombinant VEGFR-2 TRK construct but demonstrated a 7‑fold improvement in passive permeability through MDCK-MDR1 monolayers (P_app A→B 12.3 × 10⁻⁶ cm/s vs. 1.7 × 10⁻⁶ cm/s). The 4-methoxy analogue, while synthetically more accessible, exhibited a log D_7.4 of 2.4 and efflux ratio >5, limiting its utility beyond peripheral targets. Published quantitative kinase selectivity fingerprints for the exact pair (isopropoxy vs. methoxy) are not available for the full diseasome panel; internal screening against a 96‑kinase panel (radiometric assay, ATP at K_m) showed that the isopropoxy group shifts selectivity away from Abl₁ and Src toward Kit and PDGFRβ, though the mechanistic origin remains unverified by co-crystallography.

If Coupling Is Performed Without Pre-Activation Drying

Routine amide bond formation employing HATU or EDCI/HOBt in DMF or NMP proceeds without incident provided the PB-49782 lot has been dried over P₂O₅ in vacuo (≤10 mbar, 24 h) immediately prior to use. If residual water exceeds 0.8% w/w, the activated ester intermediate hydrolyses at a rate that competes with aminolysis; monitoring by LC–MS shows a 15–22% reversion to the starting acid within 2 h at 0 °C when HATU is the coupling reagent. This premature hydrolysis generates an acidic micro-environment that accelerates Boc scission, culminating in the accumulation of the unprotected pyrrolidine-amine which then reacts as a nucleophile with the remaining activated ester to produce dimeric impurities detectable at +44 Da adducts. Consequently, reactions executed in open-to-air 96-well plates without anhydrous solvent handling regularly exhibit purity reductions of 8–12% relative to septum-capped vial syntheses. Combination with primary or secondary amines requires basification to at least 1.5 equivalents of a tertiary amine (e.g., DIPEA or 2,4,6-collidine) to neutralise the carboxylic acid and prevent salt formation that retards activation. The benzofuropyrimidine ring itself withstands hydrogenation conditions (H₂ 1 atm, 10% Pd/C, EtOH, 25 °C) without furan reduction or pyrimidine ring saturation, confirmed by the persistence of the characteristic UV absorption at 288 nm and 315 nm. However, exposure to lithium aluminium hydride or BH₃·THF results in partial reduction of the pyrimidine ring, delivering a mixture of 3,4-dihydro and 1,4-dihydro regioisomers that are inseparable on silica gel and should be avoided. When scaling the final coupling to quantities exceeding 500 g, the crude product isolation frequently stalls if the anti-solvent addition rate exceeds 10% v/v per minute. Rapid precipitation generates a gelatinous, solvent-occluded mass exhibiting glass-transition broadening and a suppression of the already modest melting endotherm; vacuum oven drying at 35 °C for 72 h fails to reduce residual dichloromethane below 600 ppm, in contravention of the ICH Q3C Option 2 concentration limit. Controlled addition of n-heptane (4 volumes) over 90 min with overhead stirring at 120 rpm yields a free-flowing particulate that passes through a 250 µm sieve and retains a specific surface area of 0.9 m²/g (BET) sufficient for direct formulation blending without further micronisation. Handling on the bench: personnel should wear nitrile gloves meeting EN 374 and safety glasses; airborne fine particles may cause respiratory irritation if inhaled, though no occupational exposure limit has been formally established for this structure. Waste streams containing the compound are classified under European Waste Catalogue code 18 02 05* (chemicals consisting of or containing hazardous substances) and require incineration in a permitted facility.

**Table 2. Functional-group tolerance during downstream derivatisation of PB-49782**
Reaction Manifold	Compatible Functional Groups	Incompatible / Degradation Observed	Monitoring Technique
Amide coupling (HATU/DIPEA, DMF, 0 °C)	Alkyl amines, anilines (electron-poor), amino acid esters	Thiols (competing S-acylation), hydrazines (ring-chain tautomerism)	LC–MS (ESI+) and ¹H NMR (400 MHz)
Boc deprotection (TFA/CH₂Cl₂ 1:1, 1 h)	Amide, ester, sulfonamide, nitrile, aryl halide	Acid-labile silyl ethers, N-Trityl groups, 4,4’-dimethoxytrityl	TLC (silica, EtOAc/hexane) and ¹⁹F NMR
Hydrogenation (H₂, 10% Pd/C)	Benzofuran, pyrrolidine ring, Boc group	Benzyl esters, nitro groups (reduce), aryl bromides/iodides (dehalogenation)	UHPLC–DAD (210–400 nm)
Alkylation (NaH, alkyl halide, THF)	Carboxylate (forms ester), pyrimidine N (non-regioselective)	Alcohols (without protection), water (vigorous gas evolution)	LC–MS, microanalysis