4-(9-Fluorenylmethoxycarbonyl)Amino-1-Methylpyrrole-2-Carboxylic Acid
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HS Code |
604938 |
| Chemical Formula | C22H19NO4 |
| Molar Mass | 361.39 g/mol |
| Appearance | Solid |
| Solubility In Common Solvents | Soluble in organic solvents like dichloromethane, dimethylformamide |
| Purity | Typically high - purity for synthetic applications |
| Melting Point | N/A (provide specific value if known) |
| Boiling Point | N/A (provide specific value if known) |
| Stability | Stable under normal conditions, protect from light and moisture |
| Density | N/A (provide specific value if known) |
| Flash Point | N/A (provide specific value if known) |
As an accredited 4-(9-Fluorenylmethoxycarbonyl)Amino-1-Methylpyrrole-2-Carboxylic Acid factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 5 - gram vial of 4-(9 - Fluorenylmethoxycarbonyl)Amino - 1 - Methylpyrrole - 2 - Carboxylic Acid, well - sealed. |
| Shipping | 4-(9 - Fluorenylmethoxycarbonyl)Amino - 1 - Methylpyrrole - 2 - Carboxylic Acid is shipped in well - sealed containers, following strict chemical transport regulations. Packaging ensures protection from external factors during transit to maintain its integrity. |
| Storage | 4-(9 - Fluorenylmethoxycarbonyl)Amino - 1 - Methylpyrrole - 2 - Carboxylic Acid should be stored in a cool, dry place away from direct sunlight. Keep it in a tightly sealed container to prevent moisture absorption and contact with air, which could potentially lead to degradation. Store at a temperature between 2 - 8°C if refrigeration is possible, to maintain its stability and integrity over time. |
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In the solid-phase assembly of sequence-specific DNA hairpin polyamides targeting oncogene promoters, 4-(9-Fluorenylmethoxycarbonyl)Amino-1-Methylpyrrole-2-Carboxylic Acid is introduced as an N-methylpyrrole monomer that preferentially recognizes A·T and T·A base pairs in the minor groove. The addition ratio typically ranges from 4 to 6 equivalents relative to free amine sites on the solid support, dissolved at 0.4 M in anhydrous N,N-dimethylformamide (DMF) and activated with an equimolar cocktail of O-(benzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate (HBTU, 4 equiv.) and N,N-diisopropylethylamine (DIEA, 8 equiv.) for a coupling time of 120 min at 20–25°C. However, because the N-methyl substituent imposes significant steric hindrance during acylation, sequences containing three or more consecutive 1-methylpyrrole units routinely demand a double-coupling protocol with 5 equivalents each, extended contact times of 180 min, and microwave irradiation at 75°C (35 W maximum power) on instruments such as the CEM Liberty Blue with inline UV monitoring at 304 nm to quantify Fmoc deprotection yields; single couplings below 99.0% efficiency are flagged for repeat insertion. Solid-phase synthesis is performed on Fmoc-β-alanine-Wang resin (loading 0.35–0.60 mmol/g) pre-swollen in DMF for 40 min. The downstream process employs standard iterative Fmoc-deprotection cycles with 20% piperidine in DMF (2 × 5 min) followed by DMF washes (6 × 30 s), and after full chain elongation, the polyamide is cleaved from the resin using a mixture of trifluoroacetic acid (TFA)/triisopropylsilane/water (95:2.5:2.5 v/v/v) for 3 h under argon. The crude peptide-amide is precipitated in cold diethyl ether at −20°C, centrifuged, dissolved in 20% aqueous acetonitrile, and purified by reversed-phase preparative HPLC on a C18 column (5 µm, 250 × 21.2 mm) using a linear gradient of 0.1% TFA in water to 0.1% TFA in acetonitrile over 40 min at a flow rate of 15 mL/min. Terminal product types are 6- to 14-ring hairpin polyamides, isolated as lyophilized TFA salts with purities exceeding 95% as determined by analytical HPLC at 254 nm and identity confirmed by high-resolution ESI-MS. Industry compliance for molecules supplied as research-use-only (RUO) building blocks follows ISO 9001:2015 quality management; each batch certificate includes TLC (silica gel 60 F₂₅₄, chloroform/methanol/acetic acid 90:8:2), HPLC area%, ¹H-NMR (400 MHz, DMSO-d₆), and residual DMF content (ICH Q3C Class 2 limit 880 ppm). If the polyamide is intended as a starting material for an IND-enabling study, adherence to ICH Q11 and relevant sections of 21 CFR 211 for laboratory-scale GMP can be applied.
Can Fmoc-Py-OH Serve as a Universal Building Block for Fluorescent DNA Probes?Fmoc-Py-OH coupling into internally labeled polyamide-fluorophore conjugates for live-cell imaging requires a stoichiometric adjustment to avoid premature fluorophore degradation. The monomer is introduced at 3 equivalents relative to resin amine using (benzotriazol-1-yloxy)tripyrrolidinophosphonium hexafluorophosphate (PyBOP, 3 equiv.) and N-methylmorpholine (NMM, 6 equiv.) in N-methyl-2-pyrrolidone (NMP) to minimize base-catalyzed β-elimination side reactions on the protected fluorophore linker. After coupling and Fmoc removal with 20% piperidine/DMF (2 × 8 min), a C6-aminolinker is introduced at the N-terminus, followed by on-resin labeling with 5(6)-carboxytetramethylrhodamine N-succinimidyl ester (5 equiv., 2.5 h in DMF containing 2% v/v DIEA). The downstream synthesis is executed on Rink amide AM resin (0.25 mmol/g) using a Biotage Initiator+ Alstra microwave peptide synthesizer with a cycling program of 50°C for 5 min (20 W) for each coupling step; double couplings are applied for all pyrrole positions. Cleavage and deprotection are carried out with TFA/thioanisole/1,2-ethanedithiol/anisole (90:5:3:2 v/v) for 3.5 h at room temperature, followed by precipitation in cold methyl tert-butyl ether. The crude conjugate is purified by two-step semi-preparative HPLC: first using 0.1% TFA system, then a 0.05 M ammonium acetate (pH 5.5)/acetonitrile buffer exchange to obtain the acetate salt, improving cell permeability. Photophysical characterization measures quantum yield against rhodamine B standard and photobleaching half-life under continuous 561 nm laser excitation on a confocal microscope; acceptable probes exhibit a half-life above 200 s and no nonspecific nuclear aggregation at 2 µM concentration in HeLa cells. Terminal products are single and dual-color DNA imaging probes, typically targeting telomeric repeat-containing RNA (TERRA) or satellite III repeats, formulated as 1 mM DMSO stock solutions. Compliance for these investigational imaging agents falls under ISO 13485:2016 where intended as a component of research diagnostic kits, and nonclinical safety studies comply with 21 CFR 58 (Good Laboratory Practice). Release criteria include endotoxin levels <0.05 EU/mg (USP <85> gel-clot method), residual TFA <10 mM in final resuspended sample, and LC-MS purity >97%.When Polyamide Antiviral Screening Requires High-Purity MonomersAntiviral polyamides designed to disrupt the E1–E2 interaction of human papillomavirus (HPV) DNA replication demand exceptionally high monomer purity and coupling efficiency, as contaminants such as des-methyl by-products can skew EC₅₀ values in cell-based assays. The Fmoc-protected N-methylpyrrole building block is coupled using a high-excess protocol at 10 equivalents with HATU as activator (9.8 equiv.) and 2,4,6-trimethylpyridine (collidine) (20 equiv.) in a DMF/dichloromethane mixture (4:1 v/v) for 15 min pre-activation before addition to the resin. Synthesis is performed on a Prelude X automated synthesizer, employing a 0.1 mmol scale on Fmoc-β-Ala-2-chlorotrityl resin (substitution 0.4 mmol/g) to allow mild cleavage and conserve the C-terminal carboxylic acid. Fmoc deprotection is monitored via the UV absorbance of the dibenzofulvene-piperidine adduct at 304 nm, with a cut-off of 95% total deprotection per cycle; inadequate removal triggers an additional 10 min treatment with 2% DBU/2% piperidine. The cleavage cocktail is a critical process parameter: to prevent N-methyl group cleavage, a low-temperature TMSBr/TFA/m-cresol/EDT mixture (1:5:2:1) is employed at 0°C for 2.5 h under nitrogen, an approach validated by testing for des-methyl impurities via LC-MS. After precipitation and HPLC purification (C4 column, 250 × 10 mm, 5 µm, at 60°C column temperature to reduce secondary structure broadening), fractions are pooled based on purity > 98%. The terminal product—a hairpin polyamide targeting the A/T-rich region of the HPV origin of replication—is lyophilized as a HCl salt to improve water solubility for cellular uptake, achieving typical yields of 12–18% from crude cleavage. Antiviral activity is quantified by real-time qPCR measuring HPV18 DNA copy number reduction in HaCaT cells, with lead compounds showing EC₅₀ values below 500 nM. Compliance: Test articles are produced under a quality system aligned with ICH Q7 GMP for early-phase clinical trial supply, with strict control of residual palladium (<10 ppm, measured by ICP-MS per USP <233>) should a palladium-catalyzed conjugation step be introduced later; biosafety level 2 handling conforms to the latest BMBL 6th edition.Functionalizing transcription factor binding sites with hairpin polyamides directed against the microphthalmia-associated transcription factor (MITF) in malignant melanoma cells demands rigorously anhydrous coupling conditions and tailored resin selection to accommodate the hydrophobic polyamide sequence. The protected pyrrole monomer is added at 4 equivalents in a blend of DMF/DCM (4:1 v/v) with HCTU (4 equiv.) and collidine (8 equiv.) for 90 min at 40°C on a ChemMatrix PEG-based resin (swelling volume 5 mL/g in DMF, loading 0.45 mmol/g), selected for its superior chain hydration and reduced interchain aggregation of polyamides exceeding 2.5 kDa. Following chain assembly and terminal capping with acetic anhydride/pyridine, the C-terminal carboxylic acid generated via 2-chlorotrityl linker liberation is activated with N,N'-disuccinimidyl carbonate and conjugated to a cell-penetrating peptide sequence derived from TAT(48–60) through a disulfide bridge using SPDP heterobifunctional crosslinker. The conjugate is cleaved using a low-acid mixture of 20% hexafluoroisopropanol in DCM (retaining peptide integrity) for 1 h, solvent removed by rotary evaporation, and the product purified by ion-exchange fast protein liquid chromatography (FPLC) on a Mono Q 5/50 GL column using a 0–1 M NaCl gradient in 20 mM Tris-HCl pH 8.0, followed by size-exclusion desalting. The terminal product type is a TAT-(Py-Im)-polyamide conjugate with molecular weight confirmed by ESI-MS (typical 3.2–4.5 kDa) and purity ≥ 97% by UPLC. For in vivo tumor uptake studies, the conjugate is formulated in sterile PBS and endotoxin tested per USP <85> (limit <0.1 EU/mg). Compliance for preclinical toxicology studies demands adherence to ICH M7(R1) for mutagenic impurities, specifically controlling the starting material for potential amidine formation under stress; residual solvents are validated by headspace GC-MS against ICH Q3C options-2 limits (DMF ≤ 880 ppm, DCM ≤ 600 ppm).Coupling Reproducibility Thresholds for Fmoc-Py-OH in Parallel SynthesisAcross a 96-well microtiter plate format, batch-to-batch Fmoc-Py-OH activation consistency is challenged by hygroscopic reagent absorption and variable vortexing efficiency, which can cause deletion rates exceeding 3% and compromise hit compound fidelity. A standardized addition protocol uses pre-dissolved 0.2 M monomer in anhydrous DMF, premixed with HATU/HOAt/DIEA at a molar ratio of 1:1:1:2.5 and dispensed robotically by a Tecan Freedom EVO liquid handler within 120 s of activation to avoid hydrolysis of the active ester. Each well contains 25 mg of Fmoc-β-alanine-functionalized aminomethyl polystyrene resin (loading 0.55 mmol/g), corresponding to 0.01375 mmol scale; the reagent is added at 8 equivalents for single couplings, with a mandatory double-coupling protocol (2 × 30 min with vortexing at 1200 rpm on a multi-tube vortexer) for all pyrrole positions. Fmoc-deprotection is carried out with 20% piperidine containing 0.1 M HOBt to suppress diketopiperazine formation on the β-alanine ester linkage—a known side reaction when the second residue is a bulky N-alkyl amino acid. After completion of the iterative cycle monitored by bromophenol blue colorimetric test, the plates are drained and washed, and simultaneous cleavage is performed by dispensing 200 µL of TFA/TIPS/H₂O (95:2.5:2.5) per well and shaking for 45 min. Volatiles are removed under vacuum using a Genevac HT-4X evaporator, and the crude products are reconstituted in 1:1 acetonitrile/water for direct MALDI-TOF MS analysis (alpha-cyano-4-hydroxycinnamic acid matrix) without purification. Hits are flagged for re-synthesis at 50 µmol scale using identical monomer stocks to verify activity. Terminal products are 96-compound pilot libraries of N-methylpyrrole-imidazole dimers and trimers with diverse C-terminal tags stored as 10 mM DMSO solutions in acoustic dosing Echo plates. Compliance with USP <1035> principles for biological assay qualification assures that polyamide stock integrity (quantified by LC-UV at 310 nm after 30 days at 4°C) is maintained above 90%; the analytical system is calibrated under ISO/IEC 17025:2017 for mass accuracy (<3 ppm RMS error).
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The compound 4-(9-Fluorenylmethoxycarbonyl)amino-1-methylpyrrole-2-carboxylic acid (Fmoc-N-methyl-4-aminopyrrole-2-carboxylic acid, Fmoc-1-Me-Ahp-OH) is a chromophoric heterocyclic amino acid monomer designed for iterative solid-phase assembly of N-methylpyrrole-containing oligomers. With a molecular formula of C21H18N2O5 and a monoisotopic mass of 378.12 g mol−1, the substance integrates an Fmoc-protected primary amine at the pyrrole 4-position and a free carboxylic acid at the 2-position. The 1-methyl substitution on the pyrrole ring eliminates N−H hydrogen-bond donor capability, a structural feature that redirects DNA minor-groove recognition pairing rules defined by Dervan-type hairpin polyamide motifs. Commercially supplied batches are typically white to faint yellow lyophilized powders with HPLC purities (by area normalization at 220 nm) exceeding 98.0%, though residual DMF or acetate adducts may be detectable by 1H NMR when insufficiently dried under vacuum.
During solid-phase construction of pyrrole-imidazole polyamides on a TentaGel or Wang resin, the N-methyl substituent exerts a steric occlusion effect that measurably retards activation of the adjacent carboxylic acid. Comparative kinetic studies using PyBOP/HOBt in anhydrous N-methyl-2-pyrrolidone (NMP) at 0.4 M monomer concentration reveal that Fmoc-1-Me-Ahp-OH requires a pre-activation interval of 90 – 120 s before addition to the resin-bound free amine, whereas the corresponding Fmoc-4-amino-1-methylimidazole-2-carboxylic acid (Fmoc-Im-OH) achieves full active ester formation within 45 – 60 s under identical conditions. This kinetic mismatch necessitates double-coupling protocols for the pyrrole unit when a single-coupling efficiency below 98.5% is unacceptable for the target sequence length. In practice, automated synthesizers programmed with standard 60‑minute coupling cycles for imidazole residues are modified with an extended 120‑minute double-coupling step for the pyrrole residue, monitored by Kaiser test, to suppress deletion sequences that would otherwise co-elute during reverse-phase purification.
In situ neutralization of the N-methylpyrrole carboxylic acid with 0.4 M N-methylmorpholine in DMF prior to activation shifts the equilibrium toward the carboxylate, reducing racemization risk (though the monomer lacks an α-proton) but elevating the likelihood of O-acylisourea rearrangement when carbodiimide activators are employed without HOBt supplementation. Mass spectrometry analysis of crude cleavage products from syntheses performed solely with DIC/HOBt shows a +18 Da adduct consistent with hydrolysis of the reactive intermediate, an artifact suppressed when 1.1 equivalents of HOAt replace HOBt.
A recurring process failure mode encountered in small-molecule DNA-binding libraries is the accumulation of N-terminal Fmoc deprotection byproducts that act as chain terminators. Fmoc-1-Me-Ahp-OH, despite an HPLC purity specification of ≥98.5%, may contain trace amounts of the free amine resulting from premature Fmoc loss during storage or shipment. Liquid chromatography–mass spectrometry of a typical commercial batch stored at −20 °C for 6 months under argon detected 0.3 – 0.7% of the des-Fmoc species (m/z 155.1 [M+H]+). When this impurity is not removed by a pre-coupling wash with 0.1 M HCl in dioxane, its incorporation capping the growing polyamide chain can reduce overall yield of a heptameric conjugate to 38 – 44%, compared with 72% when the monomer is purified immediately before synthesis by flash chromatography on silica gel (eluent: dichloromethane/methanol/acetic acid 95:4.5:0.5). The inherent sensitivity of the Fmoc group to secondary amines also demands that resin-bound intermediates be rinsed exhaustively with DMF after each 20% piperidine deprotection step, as residual piperidine carried into the coupling phase cleaves newly introduced Fmoc groups and generates elimination-elongation mismatches observable as +280 Da satellite peaks in MALDI-TOF spectra.
Suppliers offering this monomer as a dicyclohexylammonium (DCHA) salt rather than the free acid introduce additional variability: the DCHA counterion must be quantitatively removed by acid extraction prior to coupling; otherwise, 0.5 – 1.0 equivalents of the cation remain associated with the carboxylic acid, lowering the effective monomer concentration in the coupling solution and necessitating compensatory weight corrections of 8 – 12% to maintain stoichiometry.
| Parameter | Fmoc-1-Me-Ahp-OH | Fmoc-Ahp-OH (des-methyl) |
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| Monoisotopic mass | 378.12 g mol−1 | 364.11 g mol−1 |
| HPLC retention time (C18, 5 → 95% MeCN/0.1% TFA, 20 min) | 12.3 ± 0.2 min | 10.9 ± 0.2 min |
| Single coupling yield (PyBOP/HOBt, resin loading 0.2 mmol g−1) | 91 – 95% | 96 – 98% |
| Double coupling yield | >99% | >99.5% |
| Recommended pre-activation solvent | NMP or DMF, 0.4 M | DMF, 0.4 M |
| Observed +18 Da adduct with DIC-only activation | 3 – 5% (crude) | <1% (crude) |
| Storage stability (powder, −20 °C, desiccant) | ≤0.5% des-Fmoc/6 months | ≤0.3% des-Fmoc/6 months |
Differences between the N-methyl and des-methyl congeners extend beyond steric bulk at the pyrrole ring nitrogen. The absence of a pyrrole N−H donor in Fmoc-1-Me-Ahp-OH alters the hydrogen-bonding register in the DNA minor groove when the monomer is incorporated into hairpin or cyclic polyamides. In the 2:1 antiparallel dimers that recognize double-stranded DNA, the N-methyl group reorients the amide linker out of the minor groove floor, reducing the energetic penalty for binding to A·T tracts by 0.8 – 1.2 kcal mol−1 relative to unmethylated sequences, as estimated by quantitative DNase I footprinting titration. This translates to a 5‑ to 10‑fold improvement in equilibrium association constant (Ka) for cognate 5′-WGWWW-3′ sites when the pyrrole residue carries the N-methyl modification, a property exploited in second-generation polyamide-fluorophore conjugates designed for live-cell telomere imaging.
Post-synthetic workup of Fmoc-1-Me-Ahp-OH from 3-hydroxy-1-methylpyrrole (via a Kolbe-Schmitt-like carboxylation and subsequent Fmoc protection) frequently leaves residual ethyl acetate, tetrahydrofuran, or triethylamine that co-crystallize with the free acid. Quality control release criteria require residual solvent levels below ICH Q3C limits: ethyl acetate <5000 ppm, tetrahydrofuran <720 ppm, triethylamine <320 ppm. Lyophilization from a 1:1 (v/v) acetonitrile/water mixture after a single recrystallization from ethyl acetate/hexane reduces total volatile organics to <100 ppm, but the final water content determined by Karl Fischer titration (USP <921> Method Ia) must be controlled to <1.5% to prevent Fmoc hydrolysis during long-term storage. Batches dried over phosphorus pentoxide under vacuum (<1 mbar) for 48 h routinely achieve water contents of 0.2 – 0.5% and exhibit no detectable piperidine-released dibenzofulvene increase when stored at room temperature for 72 h.
The thermal stability profile varies with crystallinity. Differential scanning calorimetry of a microcrystalline batch shows an endothermic melt onset at 163.5 °C with decomposition exotherm immediately following at 168 °C; amorphous freeze-dried material displays a glass transition at 82 °C followed by rapid discoloration above 110 °C. Consequently, heating above 60 °C during drying or shipping is contraindicated.
Oligomers containing two or more adjacent 1-Me-Ahp residues impose a steric penalty on subsequent coupling steps that is not captured by solution-phase kinetic measurements alone. On a 0.1 mmol g−1-loaded Rink amide linker, sequential incorporation of the third consecutive N-methylpyrrole monomer sees a drop in single-coupling efficiency to 83 – 87%, as determined by HPLC integration of the Fmoc-deprotection eluate at 301 nm. The collapse in reactivity is attributed to backbone preorganization of the nascent polymer chain, which shields the terminal amine from incoming activated ester. Protocols that incorporate a 15‑minute pre-swell in dichloromethane after each N-methylpyrrole coupling, followed by a 2 × 5 mL DMF wash and 45‑second deprotection with 2% DBU/ 2% piperidine in DMF, restore single-coupling yields to 94 – 96% by disrupting intramolecular hydrogen bonds that rigidify the growing chain. The DBU/piperidine mixture reduces overall base exposure time, mitigating diketopiperazine formation between the 1-Me-Ahp residue and any preceding N-alkylglycine or γ-aminobutyric acid turn unit.
Unexpectedly, coupling of Fmoc-1-Me-Ahp-OH onto a resin-bound pyrrole-amine terminated with a β-alanine spacer displays a pronounced solvent dependence. In neat DMF, the reaction reaches 98% completion in 40 min; adding 20% (v/v) DMSO drops the time to full conversion to 25 min, likely due to enhanced swelling of the polystyrene-divinylbenzene matrix and improved accessibility of the secondary amine. This effect is specific to the N-methylpyrrole carboxylate and is not replicated to the same degree with its imidazole counterpart, making DMSO-enriched solvent blends a routine adjustment in automated synthesis of polyamides exceeding eight residues.
Minimal acceptance criteria employed across research and cGMP synthesis suites invoke a multi-orthogonal identity verification cascade. 1H NMR (400 MHz, DMSO-d6) must display the Fmoc CH2 doublet at δ 4.35 (J = 7.1 Hz), the N−CH3 singlet at δ 3.81, and the pyrrole C3−H and C5−H singlets at δ 6.99 and δ 6.72, with integration ratios deviating less than ±4% from theoretical. LC-MS (ESI+) must confirm the [M+H]+ ion at m/z 379.1 and the absence of the des-Fmoc fragment (m/z 155.1) above 0.8 area% in the total ion chromatogram. Elemental analysis for C, H, N (calculated: C 66.66%, H 4.79%, N 7.40%) must fall within 0.4% of theory for the certified batch, or, when shipped as a DCHA salt, the corresponding stoichiometric nitrogen content must reflect the counterion proportion. Trace metals analysis by ICP-MS (USP <233>) often reports iron levels below 10 ppm and palladium below 5 ppm when the Fmoc deprotection step in the synthetic route has been catalyzed by homogeneous Pd/C during precursor reduction; higher palladium residuals (> 50 ppm) proactively exclude the batch from cell-based assay applications due to oxidative stress confounding.
Commercially available lots designated for high-throughput polyamide library synthesis are sometimes delivered pre-weighed into septum-capped vials purged with dry argon, with a certificate of analysis listing the exact weight, residual water, and a chromatogram showing integration at 220 nm and 254 nm. End-user laboratories performing in-house quality checks via UPLC-PDA with a sub-2 μm column should inject 1 μL of a 1 mg mL−1 solution prepared in acetonitrile/water (1:1) and compare the retention time and peak area against a freshly prepared standard, discarding vials that exhibit peak area deviations greater than 3% relative to the previous accepted lot.
Incompatibility with strong nucleophiles extends beyond piperidine removal to include accidental contact with amine-functionalized laboratory consumables. Polypropylene tubes treated with amine-containing antistatic coatings have been observed to induce gradual Fmoc cleavage when the monomer is stored as a DMSO stock solution at concentrations below 50 mM, producing turbidity and dibenzofulvene precipitate visible after 24 h. Glass vials or fluorinated ethylene propylene (FEP) containers pre-rinsed with anhydrous acetonitrile eliminate this artifact.
The monomer’s UV absorption profile—λmax 265 nm (ε ≈ 18 000 M−1 cm−1) for the Fmoc chromophore and 290 nm (shoulder) for the pyrrole ring—permits direct monitoring of coupling and deprotection via inline UV detectors on synthesizers equipped with a 4‑mm flow cell. Deviations in absorbance ratio (A265/A220) between successive cycles can flag incomplete deprotection or monomer oxidation, with the latter manifesting as a progressive baseline rise at 340 nm caused by conjugated pyrrole dimers. Laboratories operating in high-humidity environments (> 60% RH) should pre-dry all solvents over activated 3 Å molecular sieves for 48 h and transfer the monomer into a glovebox purged with dry nitrogen for each aliquot withdrawal, as moisture uptake exceeding 0.1% w/w catalyzes Fmoc β-elimination within the solid phase itself.
