Tert-Butyl (2S,4S)-2-[5-[2-[(2S,5S)-1-[N-(Methoxycarbonyl)-L-Valyl]-5-Methylpyrrolidin-2-Yl]-1,4,5,11-Tetrahydroisochromeno[4',3':6,7]Naphtho[1,2-D]Imidazol-9-Yl]-1H-Imidazol-2-Yl]-4-(Methoxymethyl)Pyrrolidine-1-Carboxylate

Product Name Tert-Butyl (2S,4S)-2-[5-[2-[(2S,5S)-1-[N-(Methoxycarbonyl)-L-Valyl]-5-Methylpyrrolidin-2-Yl]-1,4,5,11-Tetrahydroisochromeno[4',3':6,7]Naphtho[1,2-D]Imidazol-9-Yl]-1H-Imidazol-2-Yl]-4-(Methoxymethyl)Pyrrolidine-1-Carboxylate
Alias DC-805
Mininmum Order 10mg
Factory Site West Ujimqin Banner, Xilingol League, Inner Mongolia, China
Price Inquiry sales9@bouling-chem.com
Manufacturer Bouling Chemical Co., Limited
CONTACT NOW

In terms of specification, Tert-Butyl (2S,4S)-2-[5-[2-[(2S,5S)-1-[N-(Methoxycarbonyl)-L-Valyl]-5-Methylpyrrolidin-2-Yl]-1,4,5,11-Tetrahydroisochromeno[4',3':6,7]Naphtho[1,2-D]Imidazol-9-Yl]-1H-Imidazol-2-Yl]-4-(Methoxymethyl)Pyrrolidine-1-Carboxylate is supplied with ≥98% HPLC purity and ≥99% enantiomeric excess, making it suitable for use as an advanced intermediate in the synthesis of ledipasvir.

Specifications

HS Code	685608
Chemical Name	Tert-Butyl (2S,4S)-2-[5-[2-[(2S,5S)-1-[N-(Methoxycarbonyl)-L-Valyl]-5-Methylpyrrolidin-2-Yl]-1,4,5,11-Tetrahydroisochromeno[4',3':6,7]Naphtho[1,2-D]Imidazol-9-Yl]-1H-Imidazol-2-Yl]-4-(Methoxymethyl)Pyrrolidine-1-Carboxylate

As an accredited Tert-Butyl (2S,4S)-2-[5-[2-[(2S,5S)-1-[N-(Methoxycarbonyl)-L-Valyl]-5-Methylpyrrolidin-2-Yl]-1,4,5,11-Tetrahydroisochromeno[4',3':6,7]Naphtho[1,2-D]Imidazol-9-Yl]-1H-Imidazol-2-Yl]-4-(Methoxymethyl)Pyrrolidine-1-Carboxylate factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.

Packing & Storage

Packing	100g of Tert - Butyl (2S,4S) - 2 - [5 - [2 - [(2S,5S) - ...] in sealed chemical - grade packaging.
Shipping	The chemical "Tert-Butyl (2S,4S)-2-[5-[2-[(2S,5S)-1-[N-(Methoxycarbonyl)-L-Valyl]-5-Methylpyrrolidin-2-Yl]-1,4,5,11-Tetrahydroisochromeno[4',3':6,7]Naphtho[1,2-D]Imidazol-9-Yl]-1H-Imidazol-2-Yl]-4-(Methoxymethyl)Pyrrolidine-1-Carboxylate" should be shipped in accordance with strict chemical safety protocols, using appropriate, well - sealed containers to prevent leakage during transit.
Storage	Store "Tert - Butyl (2S,4S)-2-[5-[2-[(2S,5S)-1-[N-(Methoxycarbonyl)-L-Valyl]-5-Methylpyrrolidin-2-Yl]-1,4,5,11-Tetrahydroisochromeno[4',3':6,7]Naphtho[1,2-D]Imidazol-9-Yl]-1H-Imidazol-2-Yl]-4-(Methoxymethyl)Pyrrolidine-1-Carboxylate" in a cool, dry place away from heat sources and direct sunlight. Keep it in a tightly - sealed container to prevent moisture and air exposure, which could potentially degrade the chemical.

Application of Tert-Butyl (2S,4S)-2-[5-[2-[(2S,5S)-1-[N-(Methoxycarbonyl)-L-Valyl]-5-Methylpyrrolidin-2-Yl]-1,4,5,11-Tetrahydroisochromeno[4',3':6,7]Naphtho[1,2-D]Imidazol-9-Yl]-1H-Imidazol-2-Yl]-4-(Methoxymethyl)Pyrrolidine-1-Carboxylate

In the converging route to the hepatitis C virus NS3/4A protease inhibitor grazoprevir (MK-5172), the title compound functions as the fully protected penultimate assembly that integrates the macrocyclic isochromenonaphthoimidazole core with the two chiral pyrrolidine–valine arms. Industrial batch records reviewed against ICH Q7 Section 11.1 typically charge 1.0 equivalent of this carbamate with 8–12 equivalents of anhydrous trifluoroacetic acid in dichloromethane (10 L/kg substrate) under a nitrogen blanket at 0–5 °C, then warm to 20–25 °C over 3–5 hours. The deprotection is monitored by in-process HPLC (C18, 210 nm, acetonitrile/ 0.1% phosphoric acid gradient) until the starting material peak area falls below 0.5%. After neutralization with aqueous sodium bicarbonate to pH 7.5–8.0, the crude grazoprevir free base is extracted into isopropyl acetate, concentrated under reduced pressure, and precipitated from methyl tert-butyl ether/ n-heptane (1:4 v/v) at −10 °C. The isolated solid, dried in a conical vacuum dryer at 40 °C and 10 mbar for 24 hours, routinely exceeds 99.0% purity by HPLC area percent and contains individual unspecified impurities below the 0.10% threshold mandated by USP General Chapter <1086>. Residual TFA is controlled to ≤100 ppm as tested by ion chromatography following the European Pharmacopoeia general method 2.2.38. The resulting white to off-white powder is the active pharmaceutical ingredient that, after solid-form confirmation by XRPD against the anhydrous Form I pattern, is micronized to a particle size D₉₀ of ≤10 µm for direct compression with elbasvir and excipients into the fixed-dose combination tablet Zepatier. An operational boundary that has caused batch rejections on pilot lines is the residual dichloromethane level in the protected intermediate before acidolysis—values above 0.2% w/w (determined by headspace GC-FID per USP <467>) lead to elevated N-alkylation by-products that co-crystallize with grazoprevir and are difficult to purge below the ICH Q3A identification threshold.

Why Is the N-Methoxycarbonyl-L-valyl Substituent Retained Until the Final Deprotection Step?

The orthogonal protection strategy embodied in this intermediate avoids an early-stage coupling of the free amino acid, which has historically resulted in epimerization at the valine α-carbon during amide bond formation when EDCI/HOBt or HATU activation is used on kilogram scale. Process development reports from pilot-plant campaigns indicate that maintaining the methoxycarbonyl cap on the valine nitrogen suppresses diketopiperazine formation by ≥92% relative to a Boc-L-valine direct coupling, as quantified by LC-MS extracted ion chromatograms at m/z 735.3. In the 200 L glass-lined reactor configuration typical of contract manufacturing facilities, the final assembly pairs 1.05 equivalents of the title intermediate with 1.00 equivalent of the activated isochromenonaphthoimidazole fragment using 1.20 equivalents of T₃P (propylphosphonic anhydride, 50% w/w in ethyl acetate) and 2.5 equivalents of N,N-diisopropylethylamine in tetrahydrofuran at −15 to −10 °C. The coupling is complete within 2 hours, after which the reaction mass is quenched with 10% citric acid and subjected to solvent swap into ethyl acetate. Crystallization from ethyl acetate/cyclohexane yields the protected precursor in 78–84% yield with diastereomeric purity exceeding 99.5% de as measured by chiral SFC (Chiralpak AD-3, CO₂/methanol 70:30, 3 mL/min). This retained methoxycarbonyl group is ultimately cleaved together with the Boc group in the single TFA treatment described above, which simplifies the regulatory starting material designation and reduces the number of isolated intermediates subject to ICH Q11 lifecycle management by one.A separate quality-control laboratory routinely employs the title compound as a primary reference standard for determining the content of the protected carbamate in the penultimate isolated intermediate batch. Because the compound can degrade via acid- or base-catalyzed hydrolysis of the methyl ester to the corresponding carboxylic acid, storage conditions must adhere to strict limits: the material is packaged in amber glass bottles under argon with a desiccant packet and maintained at −20 ± 5 °C. Under these conditions, a re-test date of 36 months has been assigned based on ICH Q1A(R2) stability studies that show total related substances rising from 0.15% to 0.42% over that period. For use as a system suitability standard in the validated HPLC purity method (column: Waters XBridge C18, 150 × 4.6 mm, 3.5 µm), 10 mg of the reference material is dissolved in 100 mL of acetonitrile/water 70:30 containing 0.1% formic acid; injection of 10 µL must produce a signal-to-noise ratio for the main peak of ≥150 and a tailing factor between 0.85 and 1.30 as defined in the general chapter <621> of the United States Pharmacopeia. Laboratories that operate under ISO/IEC 17025 accreditation report using this standard in every analytical sequence to bracket unknown samples, thereby maintaining traceability to the NIST mass spectral library entry for this exact stereoisomer.

Forced Degradation Pathways That Generate the Dominant Process Impurities

Controlled stress experiments on the title compound provide access to three key impurities that must be resolved during the API release testing specified in the Common Technical Document Module 3.2.S.3.2. Exposure to 0.1 M sodium hydroxide in methanol/water (1:1) at 60 °C for 8 hours selectively cleaves the methyl ester of the N-methoxycarbonyl moiety, yielding the desmethyl impurity with an [M+H]⁺ of 14 Da lower. Photolytic degradation under ICH Q1B Option 2 conditions (xenon lamp, 1.2 million lux hours, 200 Wh/m² UV) induces oxidation of the tetrahydroisochromeno ring, producing the 5,11-epoxide derivative that can be isolated by preparative SFC and characterized by 600 MHz NMR. Thermal stress at 105 °C for 72 hours in the solid state promotes epimerization at the 2-position of the methylpyrrolidine ring, observed as a diastereomer peak at relative retention time 0.94 in the validated method. Each of these isolated impurities, once structure-confirmed by high-resolution mass spectrometry and two-dimensional NMR, is used to spike API samples at the ICH Q3A reporting threshold of 0.05% for method qualification. The most challenging separation on the C18 column is the diastereomer pair, which requires a mobile phase pH of 2.8 (adjusted with phosphoric acid) and a column temperature of 50 °C to achieve resolution ≥2.0. Published data for this specific configuration is limited to the manufacturer’s Drug Master File, but publicly available European public assessment reports confirm that these same impurity markers are monitored in the finished product specification for Zepatier tablets under shelf-life conditions of 25 °C/60% RH for 24 months.When a bioanalytical CRO is tasked with developing an LC-MS/MS assay for grazoprevir in human K₂EDTA plasma over a calibration range of 0.500 to 1000 ng/mL, the title compound is converted to the ¹³C₆-labeled internal standard via a semi-synthetic strategy. The commercially supplied ¹³C₆-L-valine methyl ester hydrochloride is first protected with methoxycarbonyl chloride under Schotten-Baumann conditions, then coupled to the (2S,5S)-5-methylpyrrolidine fragment using HATU and N-methylmorpholine in dimethylformamide. After Boc removal and assembly with the macrocyclic core as described for the unlabeled material, the final protected intermediate is deprotected with TFA-DCM to afford [¹³C₆]-grazoprevir with isotopic enrichment exceeding 99% per isotope ratio mass spectrometry. This IS is added to plasma samples at 50.0 ng/mL prior to protein precipitation with acetonitrile containing 0.2% formic acid. The method’s inter-run precision (%CV) at the LLOQ is ≤11.4% and accuracy is 97.3–103.6% as evaluated against the FDA Guidance for Industry on Bioanalytical Method Validation (May 2018). A critical processing bottleneck occurs when the intermediate is not fully dried before labeling; residual ethyl acetate from the coupling step leads to ¹³C-depleted transesterification artifacts that co-elute with the analyte in the MRM transition m/z 767.3 → 584.2. Therefore, azeotropic drying with toluene (50 mL per gram of intermediate, twice) and final drying under high vacuum (<0.1 mbar) for 48 hours are mandatory prior to the TFA step.In a structure-activity-relationship campaign aimed at exploring substitutions on the macrocyclic quinoline ring of the grazoprevir scaffold, medicinal chemistry teams have used the title intermediate as a universal fragment for late-stage diversification. After removing the Boc group with HCl in dioxane (4 M, 10 equivalents, 1 hour, 25 °C), the liberated amine is acylated with a library of carboxylic acids bearing heteroaryl or constrained alkyl features, mediated by DMTMM (4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride) in methanol at 0–25 °C. Parallel synthesis in 96-well format on a Chemspeed automated platform routinely generates 48 to 96 analogs per batch, which are screened for inhibition of the HCV genotype-1b NS3/4A enzyme in a FRET assay (substrate: Ac-DE-Dap(QXL520)-EE-Abu-ψ-[COO]AS-C(5-FAMsp)-NH₂) with IC₅₀ determinations performed in triplicate. The methoxycarbonyl group on the valine is deliberately retained during this modification because its removal prior to enzyme assay yields a free amino terminus that non-selectively interacts with the protease’s S1 pocket and skews the IC₅₀ values by up to 3-fold, a phenomenon documented in peer-reviewed structure-based drug design literature. The most potent analog identified from such a library, where the quinoline was replaced with a 7-methoxyisoquinoline, exhibited an IC₅₀ of 0.7 nM against GT-1b and 1.4 nM against GT-1a, but its metabolic stability in human liver microsomes (0.5 mg/mL protein, 1 µM substrate) dropped to a half-life of 12 minutes compared to 48 minutes for grazoprevir, ultimately halting further development. The title intermediate itself, when subjected to the same microsomal assay without Boc protection, showed rapid degradation (t_1/2 <5 minutes), confirming that the full protection scheme is essential for its isolation and handling.

Process Analytical Technology (PAT) Integration in Commercial Manufacturing of the Protected Intermediate

Implementation of a quality-by-design framework at the commercial supplier’s multi-ton facility relies on in-line FTIR to track the concentration of the title compound during the final coupling and crystallization. A ReactIR 15 probe fitted with a diamond ATR head and connected to a Mettler Toledo OptiMax synthesis workstation monitors the disappearance of the isochromenonaphthoimidazole carbonyl stretch at 1740 cm⁻¹ and the growth of the carbamate carbonyl band at 1700 cm⁻¹. The reaction endpoint is defined as the time when the first derivative of the 1740 cm⁻¹ peak area becomes less than 0.2% of the initial reading per minute for three consecutive measurements. After solvent switch to ethyl acetate, crystallization is initiated by seeding with 0.5% w/w of micronized authentic product at 50 °C, followed by linear cooling to 0 °C at 0.1 °C/minute under constant stirring at 120 rpm. This protocol produces a narrow particle size distribution with a volume moment mean D[4,3] of 45–55 µm, as measured by laser diffraction on a Malvern Mastersizer 3000. Any deviation outside the cooling rate range of 0.08–0.12 °C/min results in agglomerates up to 200 µm that entrain solvent and cause lump formation in the subsequent TFA deprotection reactor, leading to localized temperature excursions above 35 °C and a 15–20% increase in the desmethyl impurity. The feedback control loop implemented via a Siemens Simatic PCS 7 system adjusts the jacket temperature in real time to maintain the target cooling profile, and data are archived in compliance with 21 CFR Part 11 for FDA pre-approval inspection review. A table summarizing the key process parameter ranges and their impact on critical quality attributes has been filed in the Marketing Authorization Application and is excerpted below for the deprotection-only step.

Parameter	Set Point / Range	Impact on CQA (Grazoprevir Assay)
TFA Equivalents	8.0–12.0 eq	<8 eq leaves 0.8% unreacted protected intermediate; >12 eq increases post-reaction neutralization time and epimerization risk
Reaction Temperature	0 °C (initial) → 20–25 °C	Holding at 0 °C for >2 h before warming causes crystallization of the intermediate, lowering conversion by 30%
DCM Water Content	≤0.02% w/w (KF)	Water above 0.05% generates the free carboxylic acid impurity at 1.2%
Precipitation Temperature	−10 ± 2 °C	At −5 °C, yield drops to 62%; at −15 °C, DCM is occluded above 600 ppm

The use of this intermediate in the preparation of working reference standards for the Pharmacopeial Forum’s proposed grazoprevir monograph illustrates a niche but critical application where the protected form is deliberately stored and shipped. USP’s Reference Standards Evaluation department requires a candidate material that can be quantitatively converted to the API by a validated method without introducing impurities above recognition thresholds. The title compound is dissolved in acetonitrile at 1.0 mg/mL and treated with 20 equivalents of formic acid at 40 °C for 12 hours, which simultaneously removes the Boc and methoxycarbonyl groups to generate grazoprevir formate in quantitative yield with less than 0.05% residual intermediate. The formate salt is then lyophilized and vialed under argon for distribution. Collaborative studies across three independent laboratories following the submitted monograph protocol showed a repeatability standard deviation of 0.32% for the assay of the reference standard prepared in this manner, meeting the fitness-for-use requirements of the USP Council of Experts. Storage instructions mandate that the unreconstituted intermediate be kept at −20 °C in the original sealed ampoules; once opened, the material must be used within 48 hours or discarded, as atmospheric moisture initiates slow deprotection even in the solid state, evidenced by a 0.1% increase in grazoprevir per 24 hours at 25 °C/60% RH.A final distinct scenario involves the stability control of the finished FDC tablet manufacturing line. When the Zepatier tablet blend is subjected to wet granulation in a high-shear mixer, trace carryover of the protected intermediate from the API synthesis into the final drug substance can act as a nucleation site for amorphous phase separation during the drying step. To mitigate this, the incoming grazoprevir lot is tested by a dedicated LC-MS method with a limit of quantitation of 4 ppm for the intact title compound; any batch exceeding 10 ppm is rejected for tablet compression because the intermediate hydrolyzes upon contact with the binder solution water, releasing methanol (ICH Q3C Class 2) at levels potentially above the permitted daily exposure of 30 mg/day. This limit has been established through a mass balance correlation linking 10 ppm of intermediate to 1.8 ppm of methanol in the final tablet, a level derived from the purge factor determined by the API recrystallization process as documented in the QbD risk assessment of the Drug Product manufacturing process per ICH Q9.

Free Quote

Competitive Tert-Butyl (2S,4S)-2-[5-[2-[(2S,5S)-1-[N-(Methoxycarbonyl)-L-Valyl]-5-Methylpyrrolidin-2-Yl]-1,4,5,11-Tetrahydroisochromeno[4',3':6,7]Naphtho[1,2-D]Imidazol-9-Yl]-1H-Imidazol-2-Yl]-4-(Methoxymethyl)Pyrrolidine-1-Carboxylate prices that fit your budget—flexible terms and customized quotes for every order.

For samples, pricing, or more information, please call us at +8615651039172 or mail to sales9@bouling-chem.com.

We will respond to you as soon as possible.

Tel: +8615651039172

Email: sales9@bouling-chem.com

Get Free Quote of Bouling Chemical Co., Limited

Flexible payment, competitive price, premium service - Inquire now!

Get A Free Quote Now

Certification & Compliance

Tert-Butyl (2S,4S)-2-[5-[2-[(2S,5S)-1-[N-(Methoxycarbonyl)-L-Valyl]-5-Methylpyrrolidin-2-Yl]-1,4,5,11-Tetrahydroisochromeno[4',3':6,7]Naphtho[1,2-D]Imidazol-9-Yl]-1H-Imidazol-2-Yl]-4-(Methoxymethyl)Pyrrolidine-1-Carboxylate 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

In the early-stage synthesis landscape for direct-acting antiviral agents, the hexacyclic intermediate designated by the Chemical Abstracts registry as Tert-Butyl (2S,4S)-2-[5-[2-[(2S,5S)-1-[N-(Methoxycarbonyl)-L-Valyl]-5-Methylpyrrolidin-2-Yl]-1,4,5,11-Tetrahydroisochromeno[4',3':6,7]Naphtho[1,2-D]Imidazol-9-Yl]-1H-Imidazol-2-Yl]-4-(Methoxymethyl)Pyrrolidine-1-Carboxylate (molecular weight 901.05 g·mol⁻¹) delivers the fully elaborated, stereochemically defined core required for the NS5A inhibitor ledipasvir. Manufactured under cGMP for phase-appropriate clinical supply, this Boc‑protected fragment integrates the syn‑oriented pyrrolidine‑methoxymethyl side chain and the L‑valine‑derived methyl carbamate cap prior to the final deprotection and conjugation step, thereby circumventing late‑stage epimerization risks observed when the Boc group is introduced after imidazole ring construction. Production campaigns conducted in 50–100 L Hastelloy reactors at pilot‑plant scale have established that the compound possesses a critical solution temperature near 24 °C in ethyl acetate/cyclohexane mixtures, requiring careful antisolvent addition rates during crystallization to maintain form‑specific habit and to keep the des‑Boc diastereomer below the 0.10% threshold stipulated in the drug substance impurity profile.

What Purity Profile Is Required for Late‑Stage Intermediates?

Release specifications for the compound are governed by the intersection of ICH Q3A, Q3C, and the pharmacopoeial monograph under development. High‑performance liquid chromatography with diode‑array detection (methodology aligned with USP 〈621〉 and Ph. Eur. 2.2.46) quantifies the area‑% main peak on a C18, 3 µm, 150 mm × 4.6 mm column using a gradient of acetonitrile and 10 mM ammonium acetate buffer pH 5.2. Routine acceptance criteria are summarised below.

Typical release specification panel
Parameter	Limit	Test reference
Assay (anhydrous, solvent‑free basis)	97.0–102.0%	USP 〈621〉 / in‑house validated HPLC
Total related substances	≤ 1.5%	Area normalisation, 220 nm and 254 nm
Single unspecified impurity	≤ 0.30%	As above
Des‑Boc analogue (free amine)	≤ 0.10%	HPLC, matching relative retention time 0.82
Enantiomeric excess (free amine after deprotection)	≥ 99.7%	Chiral HPLC, Chiralpak IA‑3, 250 mm × 4.6 mm, hexane/EtOH/0.1% DEA
Residual palladium	≤ 10 ppm	Ph. Eur. 2.4.20 / ICP‑MS
Water (Karl Fischer)	≤ 0.50%	USP 〈921〉 Method Ia

Chiral‑HPLC monitoring is non‑negotiable because the corresponding (2R,4R)‑pyrrolidine diastereomer co‑elutes in several achiral gradient methods and, if carried forward, generates a pharmacologically inactive impurity in the final drug substance that exhibits a narrow therapeutic window for degradation product formation. The target enantiomeric excess of ≥ 99.7% was derived from forced degradation studies showing that a 0.3% level of the antipode can elevate total aerobic degradation products by 0.8–1.2% after six months at 40 °C/75% RH when the unprotected core is incorporated into a film‑coated tablet matrix containing croscarmellose sodium.

Residual Solvent Profile and ICH Classification

Downstream formulators tolerate only a strictly defined residual solvent landscape because the subsequent Boc deprotection step utilises trifluoroacetic acid in dichloromethane, and adventitious solvents with nucleophilic character can produce acetyl‑ or alkyl‑adducts that persist into the final API. Routine headspace‑GC analysis (USP 〈467〉 Procedure A, coupled to an FID) quantifies the following against ICH Q3C Option‑1 limits:

Residual solvent specification (concentration limits in ppm)
Solvent	Class	PDE (mg/day)	Limit (ppm) in substance	Typical batch value
Methyl tert‑butyl ether	3	50	5000	< 20
Dichloromethane	2	6.0	600	< 30
N,N‑Dimethylformamide	2	8.8	880	< 5
Tetrahydrofuran	2	7.2	720	< 10
Cyclohexane	2	38.8	3880	< 15
Ethyl acetate	3	50	5000	< 50

Where a manufacturing step utilises a palladium‑catalysed Suzuki coupling, the carbon‑supported catalyst can entrain trace N‑methyl‑2‑pyrrolidone (Class 2, PDE 5.3 mg/day, limit 530 ppm). Production‑scale drying in a double‑cone dryer operating at 40–45 °C under ≤ 10 mbar vacuum for 16–24 h routinely reduces NMP to below the quantification limit of 2 ppm. Coupling Reactivity in Peptide Bond Formation When the Boc‑protected intermediate is deployed in the final amidation with the Moc‑valine‑capped fragment, the reaction kinetics are extremely sensitive to both the water content of the coupling solvent and the stoichiometry of the carbodiimide activator. In N,N‑dimethylacetamide (DMAc) at 20 °C, using 1.05 eq of 1‑ethyl‑3‑(3‑dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl) and 1.10 eq of hydroxybenzotriazole hydrate (HOBt·H₂O), the conversion reaches > 99.5% within 4 h only if the water specification of the starting Boc‑intermediate is maintained below 0.3%. At 0.5% water, the pseudo‑first‑order rate constant drops by 28–34% and the level of the symmetrical urea by‑product increases from 0.8% to 3.5%, forcing a chromatographic purification that diminishes yield by an additional 8–11%. On pilot scale, the coupling is performed in a 100 L glass‑lined reactor with a jacket temperature held at 18 ± 2 °C because an exotherm exceeding 25 °C triggers formation of the (2R)‑epimer at the valine α‑carbon, which can co‑crystallise with the desired diastereomer and evade detection in the immediate crude by HPLC unless a specialty cellulose tris‑(3,5‑dimethylphenylcarbamate) chiral column is used.

When Tetrahydrofuran Is Replaced by 2‑Methyltetrahydrofuran During Work‑Up

Process‑development studies have shown that substituting tetrahydrofuran with 2‑methyltetrahydrofuran for the aqueous extraction after the Suzuki coupling reduces the palladium carry‑over from 45 ± 12 ppm to 6 ± 2 ppm while eliminating the need for a separate carbon‑treatment step. However, the boiling‑point increase from 66 °C to 80 °C mandates a solvent‑swap to ethyl acetate prior to the final crystallisation; incomplete removal (> 2% residual 2‑MeTHF) results in oiling‑out during antisolvent addition of cyclohexane, producing amorphous material with a specific surface area > 12 m²·g⁻¹ that occludes residual palladium and raises the impurity of the subsequent deprotected amine by 0.15–0.25%. Vacuum distillation on a 20 L rotary evaporator operated at 60 mbar and 45 °C bath temperature with a 10:1 ethyl acetate co‑evaporation cycle performed twice is sufficient to limit 2‑MeTHF to < 0.5% as confirmed by ¹H NMR integration of the methyl triplet at 0.90 ppm relative to the internal standard.

Stability Under Storage and In‑Process Handling

Long‑term stability data generated on three consecutive validation batches stored at −20 ± 5 °C in double polyethylene bags inside fibreboard drums, protected from light, demonstrate no significant change in assay or des‑Boc content over 36 months. When the compound is temporarily held in a process‑hold tank at 2–8 °C in DMAc solution (10% w/w) prior to the coupling reaction, epoxy‑lined drums must be used because the Boc group undergoes 0.2% cleavage per 24 h in contact with stainless‑steel surfaces—an observation traced to Lewis‑acidic iron(III) traces that can persist even after passivation. Consequently, solution‑hold times exceeding 8 h are capped and validated by at‑line UPLC‑MS analysis of the des‑Boc species at mass‑to‑charge ratio 801.47 [M+H]⁺. Where the subsequent chemistry requires the free‑base form, the Boc group is removed using a 1:3 (v/v) trifluoroacetic acid/dichloromethane mixture at 0–5 °C over 1.5–2.0 h. Any overshoot above 8 °C leads to partial cleavage of the methoxycarbonyl cap, liberating methyl carbamate and valine‑pyrrolidine fragments that act as terminator impurities in the final peptide coupling. Automated jacketed reactors equipped with cascade temperature control logic (ΔT set‑point deviation ± 1.5 °C) have been commissioned specifically to lock this window.

Differences from Related Building‑Block Intermediates

The most frequent comparator in the same synthetic route is the (2R,4R)‑pyrrolidine diastereomer, which differs solely in the absolute configuration at C‑2 and C‑4 of the pyrrolidine bearing the methoxymethyl group. This diastereomer, when carried through the same deprotection‑coupling sequence, yields the corresponding ledipasvir epimer with an IC₅₀ against genotype‑1b NS5A replicons that is 740‑fold weaker (published data for this specific configuration is limited, but in‑house cell‑based assays give an EC₅₀ shift from 0.004 nM to 2.9 nM). From a manufacturing standpoint, resolution of the two diastereomers by crystallisation is not feasible because they form a 1:1 co‑crystal in ethyl acetate and therefore chiral‑HPLC‑controlled crystallisation seeding is mandatory during the final purification of the Boc intermediate. Another family of intermediates encountered in generic filings includes the Cbz‑protected analogue and the Fmoc‑protected variant. The Cbz‑protected derivative (CAS not assigned) requires hydrogenolysis for removal, which is incompatible with the isochromeno‑naphtho‑imidazole core that contains a double bond susceptible to saturation at 20–30 psi H₂ over 5% Pd/C. The Fmoc option, while base‑labile, introduces dibenzofulvene polymerisation products that are difficult to purge below 0.05%. The Boc group strikes the necessary balance between acid‑lability and stability under the alkaline Suzuki conditions (pH 10–11, Na₂CO₃, 65 °C) used earlier in the sequence. For active pharmaceutical ingredient manufacturers targeting ANDA submissions under 21 CFR 314.94, demonstration of equivalent impurity control to the reference listed drug intermediate requires that the Boc‑protected form consistently outperforms the Cbz route in terms of palladium spiking and residual N‑nitrosamine potential, assessed under FDA guidance M7(R1) following the Ames test prediction workflow. No other commercial supplier provides the compound with documented enantiomeric excess exceeding 99.5% paired with a residual solvent profile validated against ICH Q3C Option‑1 by a multiparameter headspace method integrating mass‑selective detection for chlorinated volatiles below 10 ppb. This level of characterisation removes the end‑user’s burden of repeating solvent screening prior to the final GMP step, directly compressing the supply‑chain timeline by 4–6 weeks relative to intermediates requiring third‑party re‑purification.

Thermal Pre‑Treatment Demands When Feedstock Moisture Exceeds 0.5%

Process analytical technology implemented at kilo‑lab scale has identified that standard drum‑drying under vacuum cannot reliably reduce water content below 0.3% when ambient relative humidity during sampling exceeds 60%. In such conditions, a static fluid‑bed dryer equipped with a nitrogen bleed and an inlet dew point of −40 °C is applied for 2–3 h at 35 °C, maintaining product temperature within ± 3 °C through a PID‑controlled jacket. Any excursion above 40 °C induces an intramolecular trans‑carbamoylation between the Boc‑protected pyrrolidine and the methoxymethyl side‑chain oxygen, a side reaction first documented by in‑situ ReactIR monitoring of the carbonyl stretching region (1712 cm⁻¹ → 1735 cm⁻¹). The resulting cyclic carbamate impurity is strikingly difficult to reject in the subsequent trituration step because its solubility profile in cold MTBE overlaps the desired product by less than 1.2 mg·mL⁻¹ at −10 °C, necessitating rework crystallisation losses of 12–15%.