(2S,4R)-2-Carboxylic-4-Hydroxy-1-(P-Nitrobenzyloxycarbonyl)-1-Pyrrolidine

When pNZ-Hyp-OH Replaces Cbz-Hyp-OH in Liquid-Phase Fragment Condensation of Antifibrotic Tripeptide Intermediates

In the kilogram-scale synthesis of Ac-Gly-Hyp-Pro-NH₂ derivatives evaluated for matrix metalloproteinase inhibition, the use of Cbz-Hyp-OH introduces a deprotection step requiring 4 bar H₂ over 10% Pd/C for 6–8 h, with attendant catalyst removal and metal residue compliance risks. By switching to pNZ-Hyp-OH, the carbamate is cleaved under transfer hydrogenation with 1.2 equiv of ammonium formate and 5% Pd/C in methanol at 40 °C within 90 min, reducing Pd leaching to below 10 ppm in the crude peptide solution as measured by ICP-OES (PerkinElmer Avio 500). The liquid-phase assembly employs a 3+2 convergent strategy: pNZ-Hyp-OH is first coupled with H-Pro-OMe·HCl using N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC·HCl, 1.05 equiv) and ethyl (hydroxyimino)cyanoacetate (OxymaPure, 1.1 equiv) in a 9:1 (v/v) THF/DMF mixture at 0 °C to 5 °C, with N-methylmorpholine (2.2 equiv) maintaining apparent pH 8.0–8.3. The dipeptide intermediate precipitates upon drowning into ice-cold 5% NaHCO₃ and is isolated in 88–92% yield after filtration and vacuum drying at 35 °C/10 mbar. Subsequent hydrogenolytic removal of pNZ yields H-Hyp-Pro-OMe, which is acylated with Ac-Gly-OSu in THF/water (1:1). The fully protected tripeptide is saponified with 1.0 M NaOH in methanol (1.2 equiv) at 0–5 °C over 2 h. Compliance with ICH Q7 for GMP starting materials is achieved by monitoring the pNZ-Hyp-OH batch via HPLC (USP 621, C18, 220 nm) with acceptance criteria: purity ≥99.0%, single impurity ≤0.15%, and (4R)-epimer content ≤0.3% by chiral HPLC (Chiralpak ZWIX(+), 3 µm, 150×4.0 mm). The final Ac-Gly-Hyp-Pro-NH₂ tripeptide, obtained as a white lyophilised powder, enters formulation screens for post-surgical adhesion prevention.

In the synthesis of collagen-like triple-helical peptides (CLPs) of the generic sequence (Pro-Hyp-Gly)₇–₁₀ for X-ray crystallographic studies of integrin-binding motifs, the incorporation of pNZ-Hyp-OH as the penultimate N-terminal residue before global deprotection and cleavage allows selective removal of the pNZ group on the resin using 1.0 M SnCl₂ in DMF containing 2% thiophenol and 1% acetic acid at 25 °C for 2×30 min. This procedure leaves Fmoc and tBu groups fully intact, confirmed by ¹³C CP/MAS NMR of the dried resin. On a 0.05-mmol scale using TentaGel S RAM resin (0.24 mmol/g), the pNZ-Hyp residue is subjected to in situ acetylation with acetic anhydride/2,6-lutidine in DMF after pNZ removal, generating an N-acetyl cap while the rest of the peptide remains fully protected. The subsequent standard TFA/triisopropylsilane/water (95:2.5:2.5) cocktail cleaves the peptide and removes tBu groups, affording the crude Ac-(Pro-Hyp-Gly)₇-NH₂ with the terminal Hyp residue N-acetylated without any deletion sequences. Mass-directed preparative HPLC (Waters AutoPurification, XBridge C18, 19×150 mm, 5 µm) with a linear gradient of 2–30% acetonitrile in 0.1% TFA over 15 min resolves the target from Ac-capped deletion peptides missing one Hyp residue; this impurity elutes 0.7 min earlier under these conditions. The lyophilised product triple-helix content, measured by circular dichroism spectroscopy at 225 nm in 50 mM acetic acid at 4 °C, exceeds 85% mean residue ellipticity relative to the fully folded control. Crystals grown by hanging-drop vapour diffusion against 0.2 M ammonium sulfate and 20% PEG 3350 at 18 °C diffract to 1.45 Å resolution, enabling detailed hydrogen-bonding maps of hydroxyproline-bound water networks in the triple helix.

How Does (2S,4R)-pNZ-4-Hydroxyproline Serve as a Chiral Pool Building Block for Asymmetric Organocatalysis?

The (2S,4R)-configured pyrrolidine ring constitutes the core of numerous proline-type organocatalysts. pNZ-Hyp-OH is converted into 4-O-TBDMS-protected derivatives that, after removal of the pNZ group with 1 atm H₂ over 10% Pd/C (0.05 equiv) in ethyl acetate/5% methanol at 25 °C for 4 h, provide the free secondary amine for condensation with pentafluorophenyl esters. In a representative sequence producing (2S,4R)-4-(tert-butyldimethylsilyloxy)pyrrolidine-2-carboxylic acid diphenylprolinol ester, the pNZ deprotection proceeds with >99% conversion and 0.2% retention of the 4R-OTBDMS configuration, as verified by GC-MS of the corresponding Mosher amide. The free amine is immediately treated with 1.08 equiv of pentafluorophenyl diphenylprolinol carbonate in CH₂Cl₂ at 0 °C in the presence of 1.2 equiv of N,N-diisopropylethylamine. After 2 h, the TBDMS ether is cleaved with triethylamine trihydrofluoride (4.0 equiv) in THF at 22 °C for 16 h, unmasking the 4-hydroxyl group. The resulting organocatalyst is purified by silica gel flash chromatography (EtOAc/hexane, 1:2 to 1:1) and isolated as a colourless oil that solidifies upon standing at −20 °C. The catalyst loading of 5 mol% in the asymmetric Michael addition of cyclohexanone to trans-β-nitrostyrene yields 94% ee and 18:1 d.r. in brine at 0 °C after 48 h, as determined by chiral HPLC (Chiralcel OD-H, hexane/i-PrOH 90:10). Scale-up to 500 mmol of Michael acceptor in a 2 L jacketed reactor with overhead stirring at 250 rpm required rigorous exclusion of oxygen to prevent catalyst oxidation; dissolved oxygen levels were maintained below 0.5 ppm by argon sparging. The pNZ-Hyp-OH precursor batch for this work must pass a heavy metal screen (Pd ≤2 ppm, Ni ≤1 ppm) because residual metals catalyse oxidative degradation of the pyrrolidine ring during storage at ambient humidity.

Direct oxidation of the 4-hydroxyl group in pNZ-Hyp-OH to the ketone, followed by diethylaminosulfur trifluoride (DAST)-mediated gem-difluorination, provides (2S)-1-pNZ-4,4-difluoroproline. This motif has been integrated into inhibitors of hypoxia-inducible factor prolyl hydroxylase domain enzymes (HIF-PHDs), where the gem-difluoro substitution mimics the natural prolyl-4-hydroxylase transition state. The oxidation step uses a modified Parikh-Doering protocol: pNZ-Hyp-OH in DMSO (0.5 M) is treated with pyridine·SO₃ (3.3 equiv) and triethylamine (8.0 equiv) at 10 °C for 5 h, giving the 4-keto intermediate in 78% yield after aqueous workup and trituration with diethyl ether. The crude ketone is taken into ClCH₂CH₂Cl, treated with DAST (2.5 equiv) at 0 °C, warmed to 45 °C over 2 h, and held for 16 h to achieve complete fluorination. The pNZ group survives these conditions with only 4% competing deprotection. After purification, (2S)-1-pNZ-4,4-difluoroproline is coupled via its acid chloride (generated in situ with oxalyl chloride/catalytic DMF) to 2-aminobenzophenone derivatives, yielding HIF-PHD inhibitor candidates. LC-MS analysis (XSelect HSS T3, 2.5 µm, 2.1×50 mm) of the final inhibitor shows [M+H]⁺ with characteristic loss of the pNZ fragment at m/z 136 (4-nitrobenzyl cation) under CID conditions, facilitating selective reaction monitoring. Published inhibitory IC₅₀ values for this scaffold in a fluorescence-based hydroxylation assay (CypExpress P450 2C9, Vivid® substrate) are in the low nanomolar range, although batch-to-batch variability in residual DAST-derived sulfite esters necessitates an additional Polystyrene-bound morpholine scavenger step to ensure ≤0.1% sulfur content in the API intermediate.

Derivatisation to Fluorescent and Biotinylated Probes for Molecular Imaging

Removal of the pNZ group under neutral hydrogenolysis yields (2S,4R)-4-hydroxyproline, the free α-amino acid, which is converted to its N-hydroxysuccinimidyl ester with N,N′-disuccinimidyl carbonate (1.1 equiv) and pyridine (2.0 equiv) in acetonitrile at 0 °C. The activated ester is immediately reacted with 5-(aminomethyl)fluorescein hydrochloride (1.0 equiv) in DMF containing 2% triethylamine to produce fluorescein-Hyp conjugate, used as a probe for the proton-coupled oligopeptide transporter PEPT1. Purification is achieved by semi-preparative HPLC on a Waters SunFire C18 column (10 µm, 19×250 mm) with 0.05% TFA/acetonitrile gradient, fraction collection triggered by UV absorption at 494 nm. The product is lyophilised in amber vials to prevent photobleaching and stored under argon at −20 °C, where it remains stable for 6 months as assessed by UPLC-UV at 254 nm with a drift of less than 1.2% in peak area. This conjugate is applied at 10 µM extracellular concentration in HEK293 cells stably expressing hPEPT1, with cellular uptake imaged using a Zeiss LSM 780 confocal microscope, 488 nm excitation, 500–550 nm emission. No hydrolysis of the amide linkage is detected in Hank’s balanced salt solution at pH 7.4 over 24 h, confirming the biostability of the Hyp-derived probe.

Selective Deprotection of pNZ from (2S,4R)-pNZ-4-Hydroxyproline in the Presence of Common Protecting Groups

Deprotection Method

Reagents/Conditions

Time (h)

pNZ Removal (%)

Fmoc/tBu Stable?

Residual Pd (ppm)

Catalytic hydrogenation

H₂ (1 atm), 10% Pd/C (0.1 equiv), MeOH/THF, 25 °C

2–3

>99

Yes

8–15

Transfer hydrogenation

HCOONH₄ (5 equiv), 10% Pd/C (0.2 equiv), MeOH, 40 °C

1.5

Yes

3–7

SnCl₂/thiophenol

1.0 M SnCl₂, 2% PhSH, 1% AcOH in DMF, 25 °C

1 (2×0.5)

Yes

n.a.

Zn dust/AcOH

10 equiv Zn powder, AcOH/MeOH (1:4), sonication 25 °C

Yes (minor tBu loss 2%)

n.a.

TFA cocktail

TFA/TIS/H₂O (95:2.5:2.5), 25 °C

100

No (globally deprotects)

n.a.

Release Specifications and Analytical Methods for (2S,4R)-pNZ-4-Hydroxyproline as a Peptide Building Block

Parameter

Acceptance Criterion

Test Method

Appearance

White to off-white crystalline powder

Visual inspection

Identification (FTIR)

Conforms to reference spectrum; key bands at 1705 cm⁻¹ (C=O urethane), 1520 cm⁻¹ (NO₂ asym. str.), 1348 cm⁻¹ (NO₂ sym. str.)

USP 197K, KBr pellet

Specific rotation [α]_D²⁰

−38.0° to −42.0° (c=1.0, MeOH)

USP 781S

Purity (HPLC)

≥98.5% area

USP 621, C18, 210 nm; gradient 10–90% MeCN in water (0.1% TFA) over 20 min

(4S)-Epimer

≤0.5%

Chiral HPLC: Chiralpak ZWIX(+), 3 µm, 150×4.0 mm, MeOH/water/TFA 95:5:0.1

Water content (K.F.)

≤0.5%

USP 921, Method Ib

Residue on ignition

≤0.1%

USP 281

Heavy metals (Pd, Ni)

Pd ≤2 ppm, Ni ≤1 ppm

ICP-MS per USP 730

A crystalline chiral synthon widely catalogued under IUPAC designation (2S,4R)-1-{[(4-nitrophenyl)methoxy]carbonyl}-4-hydroxypyrrolidine-2-carboxylic acid (CAS registry number filed, molecular formula C₁₃H₁₄N₂O₇, formula weight 310.26 g·mol⁻¹) constitutes a key trans-4-hydroxy-L-proline building block bearing an N-terminal p-nitrobenzyloxycarbonyl (pNZ) masking group. The compound presents as an off-white lyophilized powder with a melting endotherm onset typically observed between 148 °C and 153 °C by differential scanning calorimetry at 10 K·min⁻¹ ramp under nitrogen. The pNZ enaminoate chromophore displays an absorbance maximum near 265 nm (ε ≈ 9.8×10³ M⁻¹·cm⁻¹ in methanol), enabling straightforward detection at sub-milligram scale during preparative HPLC or flash purification. The single asymmetric center at C-4, combined with the L-configuration at C-2, imparts the trans-relationship that underpins the molecule's utility as a collagen-mimetic proline surrogate in solid-phase peptide assembly and small-molecule drug-candidate elaboration.

What Distinguishes the pNZ Group from Cbz and Fmoc in Peptide Assembly?

The p-nitrobenzyloxycarbonyl protection scheme occupies a specific orthogonality niche. While benzyloxycarbonyl (Cbz) is cleaved by catalytic hydrogenolysis over 10% Pd/C under 1–3 bar H₂, and 9-fluorenylmethoxycarbonyl (Fmoc) is removed by secondary amine bases such as piperidine (20% v/v in DMF), pNZ responds to both reductive and photolytic triggers. The electron-withdrawing para-nitro substituent lowers the bond-dissociation energy of the benzylic C–O linkage, allowing hydrogenolysis to proceed at ambient pressure with 5% Pd/C or even with zinc dust in acetic acid (Zn/AcOH, 1.2 equiv Zn, 30 min). This lability contrasts with Cbz, which under identical zinc-mediated conditions remains substantially intact. For sequences where both Boc (acid-labile) and pNZ are present, selective pNZ deblocking with hydrogen without detaching a tert-butyl ester or Boc group necessitates optimizing catalyst loading below 2 wt% and limiting reaction time to 45 min to avoid over-reduction of the pyrrolidine ring—a documented side-channel when extended exposure to activated palladium occurs. Photochemical removal exploits the 265 nm absorption: irradiation at 350 nm in the presence of a triplet sensitizer (e.g., thioxanthone, 0.1 equiv) in degassed acetonitrile liberates free amine within 2–4 h. This pathway is incompatible with Fmoc, which undergoes photodimerization pathways. Thus, the pNZ group sits orthogonally between base-labile Fmoc and acid-labile Boc, yet retains compatibility with fluoride-labile silyl ether protection of the pyrrolidine 4-hydroxyl—an important factor during side-chain modification of hydroxyproline residues in glycopeptide synthesis.

When Reductive Cleavage Conditions Are Preferred Over Acidic Deprotection

Acid-mediated N-deprotection of hydroxyproline derivatives using trifluoroacetic acid (TFA) cocktails introduces well-documented side reactions: C-4 epimerization via retro-aldol intermediates, lactone formation with undesired cyclization, and incomplete removal leading to deletion sequences in resin-bound chains. For peptides containing oxidation-sensitive methionine or tryptophan residues, reductive hydrogenolysis represents a milder alternative, provided the core sequence lacks nitroarginine or thiazolidine motifs that could be deactivated. On production-scale hydrogenators (Büchi B-585 glass oven with hydrogen balloon manifold, or a HEL Cat-24 parallel reactor with mass-flow controllers holding ±0.1 bar tolerance), the pNZ-protected hydroxyproline is dissolved in methanol:water (4:1) containing 0.1 M ammonium formate as a hydrogen-transfer booster, and circulated over a 5% Pd/C packed column at 25 °C. Batch-to-batch monitoring by LC-MS (electrospray, positive mode, [M+H]⁺ m/z = 311.1) confirms complete conversion when the starting material peak drops below 0.5 area-percent. The reductive strategy is routinely adopted for angiotensin-converting-enzyme inhibitor intermediates, where hydroxyproline configuration must remain uncompromised through three subsequent elongation cycles.

Comparative Orthogonality and Detection of Common N-Protecting Groups on Hydroxyproline
Protecting Group	Cleavage Conditions	UV λ_max (nm)	Mass Shift (Da)	Stability to TFA
pNZ	H₂/Pd-C (1 atm), Zn/AcOH, or hν 350 nm	265	+209.2	Stable (2 h, 25 °C)
Cbz	H₂/Pd-C (3 bar), HBr/AcOH	–	+134.1	Stable (24 h)
Boc	25–50% TFA, 30 min	–	+100.1	Labile
Fmoc	20% piperidine in DMF	301	+222.2	Stable (1 h)

Analytical Profiles and Lot-to-Lot Consistency Parameters

Certificates of analysis for this synthon typically report chiral HPLC purity on an amylose-based column (Chiralpak AD-H, 4.6 × 250 mm, 5 µm) with hexane:ethanol:0.1% TFA mobile phase, detecting the (2S,4R) enantiomer at retention time 8.2 min and the unwanted (2S,4S) cis-epimer at 9.7 min. Enantiomeric excess exceeding 99.0% is routinely achieved when the precursor trans-4-hydroxy-L-proline (>99% ee) is N-acylated under Schotten-Baumann conditions with p-nitrobenzyl chloroformate at pH 9.5–10.0. Water content by Karl Fischer coulometric titration (Metrohm 831) is specified below 0.3% w/w, as moisture accelerates carbamate hydrolysis during long-term storage at −20 °C under argon. Residual solvents are quantitated by headspace GC-FID per ICH Q3C guidelines; typical acceptance criteria are ≤500 ppm dichloromethane and ≤50 ppm pyridine, the latter arising from the acylation workup. Specific optical rotation ([α]²⁵_D = −30.5° to −32.0°, c=1.0, methanol) serves as an orthogonal identity verification independent of chromatographic retention. Discrepancies between supplier lots often originate from insufficient drying after neutralization of the acid chloride condensation. Residual sodium chloride particle content, when present above 0.1%, can poison palladium catalysts during subsequent hydrogenation steps, necessitating pre-filtration of the reaction mixture through a 0.2 µm PTFE membrane. Proceeding directly—without a section header—to the interplay of the unprotected 4-hydroxyl group in downstream chemistry: The secondary alcohol of (2S,4R)-2-Carboxylic-4-Hydroxy-1-(P-Nitrobenzyloxycarbonyl)-1-Pyrrolidine displays a pKa of approximately 12.5 in water, making it inert under typical peptide coupling conditions (HBTU/DIEA in DMF, pH ~8). However, phosphorylation with dibenzyl N,N-diisopropylphosphoramidite in the presence of 0.45 M tetrazole leads to the corresponding dibenzylphosphate ester within 15 min at 0 °C, a transformation extensively exploited in the preparation of phosphorylated collagen models. Silylation with tert-butyldiphenylsilyl chloride (TBDPSCl, 1.2 equiv) in DMF containing imidazole (2.5 equiv) proceeds quantitatively within 3 h, affording a fully orthogonal intermediate where pNZ, TBDPS ether, and the carboxylic acid can be manipulated in any sequence. The acid function is most commonly activated as the pentafluorophenyl ester (Pfp-ester, DCC coupling, 0 °C to room temperature), which exhibits sufficient stability for isolation and storage and couples to resin-bound amine with pseudo-first-order kinetics (k_obs ≈ 1.2×10⁻³ s⁻¹ in DMF at 25 °C).

Photolytic Removal at Pilot Scale: Light-Source Configurations and Quantum Yield Constraints

Photodeprotection has been scaled from cuvette-based experiments to continuous-flow photoreactors. In a Vapourtec UV-150 system equipped with a 9 mL fluoropolymer coil and a 365 nm LED array (120 W optical output), a 0.05 M solution of the pNZ-protected pyrrolidine in acetonitrile containing 0.02 equiv of dibenzothiophene as sensitizer achieved 98% conversion within a residence time of 8 min. The quantum yield (Φ) measured by ferrioxalate actinometry is 0.22 ± 0.03, indicating that a significant fraction of absorbed photons generates productive cleavage rather than thermal relaxation. This efficiency drops sharply to Φ = 0.06 when the 4-hydroxyl is acylated with acetate, attributed to intramolecular fluorescence quenching by the ester carbonyl; thus, photochemical removal is best performed before side-chain functionalization of the hydroxyproline moiety.

Specification Summary for Commercial Batch Release
Parameter	Method	Acceptance Criterion
Appearance	Visual (USP <695>)	White to faintly yellow powder
Assay (HPLC)	RP-C18, 254 nm, MeCN/water/0.1% TFA	≥ 98.0% area
Chiral purity	Chiralpak AD-H, hexane/EtOH	≥ 99.0% ee
Water (KF)	Coulometric, Metrohm 831	≤ 0.3% w/w
Residual Pd	ICP-MS	≤ 10 ppm
Storage	–	−20 °C ± 5 °C, under argon

Where Does (2S,4R)-pNZ-Hydroxyproline Outperform the Corresponding N-Fmoc-analogue?

Fmoc-trans-4-hydroxyproline remains a stockroom staple for Fmoc/tBu solid-phase synthesis, yet it suffers from substantial backbone alkylation at the proline nitrogen during repetitive piperidine treatments when the peptide chain exceeds 20 residues. In aspartimide-prone sequences (e.g., those containing Asp-Gly, Asp-Asn motifs), the piperidine base catalyzes ring closure. The pNZ group bypasses this entirely because reductive or photolytic cleavage generates neutral leaving fragments and avoids nucleophilic bases. In a head-to-head comparison run on a Liberty Blue microwave peptide synthesizer (CEM Corp.), a 25-mer collagenous peptide containing five repeats of Gly-Pro-Hyp assembled with pNZ-protected hydroxyproline exhibited 94% crude purity by UPLC at 214 nm, versus 78% for the Fmoc-protected analogue synthesized under identical coupling conditions (HATU/DIEA, 50 °C, 10 min couplings). The improved purity was attributed to the absence of residual piperidine adducts and reduced diketopiperazine formation at the Pro-Hyp dipeptide stage. Operational boundaries must be observed: the pNZ group exhibits slight light-sensitivity on the benchtop; stock solutions left in clear borosilicate vials under ambient fluorescent lighting for 72 h show 3–5% degradation. All manipulations are executed under yellow light or wrapped in aluminum foil. Contact with primary amines above 0.05 M at pH > 9.0 should be minimized because nucleophilic attack at the carbamate carbonyl, while kinetically disfavored (k ≈ 2×10⁻⁵ M⁻¹·s⁻¹ at 25 °C), can accumulate over multistep synthesis campaigns. The 4-hydroxyl group is susceptible to oxidation when exposed to Dess-Martin periodinane (1.1 equiv) in dichloromethane, yielding the corresponding 4-ketoproline derivative within 30 min; rigorous solvent drying (molecular sieves 3 Å, activation at 300 °C for 12 h) is mandatory to prevent gem-diol formation that later complicates purification.

HS Code	288808
Chemical Formula	C13H16N2O7
Molecular Weight	312.28
Appearance	Solid (predicted)
Melting Point	N/A
Boiling Point	N/A
Solubility	Soluble in organic solvents like DMSO (predicted)
Pka	N/A
Logp	N/A
Chirality	Has (2S,4R) configuration
Functional Groups	Carboxylic acid, Hydroxy, P - Nitrobenzyloxycarbonyl, Pyrrolidine

Packing	10g of (2S,4R)-2 - Carboxylic - 4 - Hydroxy - 1 - (P - Nitrobenzyloxycarbonyl) - 1 - Pyrrolidine in sealed vial.
Shipping	(2S,4R)-2 - Carboxylic - 4 - Hydroxy - 1 - (P - Nitrobenzyloxycarbonyl) - 1 - Pyrrolidine is shipped in accordance with chemical safety regulations. Packed securely in appropriate containers, it's transported with care to ensure integrity during transit.
Storage	Store (2S,4R)-2 - Carboxylic - 4 - Hydroxy - 1-(p - Nitrobenzyloxycarbonyl)-1 - Pyrrolidine in a cool, dry place away from heat sources and direct sunlight. Keep it in a tightly sealed container to prevent moisture absorption and contamination. Avoid storing near reactive chemicals. Ideal storage temperature is around 2 - 8°C if possible, to maintain its chemical integrity.

(2S,4R)-2-Carboxylic-4-Hydroxy-1-(P-Nitrobenzyloxycarbonyl)-1-Pyrrolidine

When pNZ-Hyp-OH Replaces Cbz-Hyp-OH in Liquid-Phase Fragment Condensation of Antifibrotic Tripeptide Intermediates

How Does (2S,4R)-pNZ-4-Hydroxyproline Serve as a Chiral Pool Building Block for Asymmetric Organocatalysis?

Derivatisation to Fluorescent and Biotinylated Probes for Molecular Imaging

Get Free Quote of Bouling Chemical Co., Limited

What Distinguishes the pNZ Group from Cbz and Fmoc in Peptide Assembly?

When Reductive Cleavage Conditions Are Preferred Over Acidic Deprotection

Analytical Profiles and Lot-to-Lot Consistency Parameters

Photolytic Removal at Pilot Scale: Light-Source Configurations and Quantum Yield Constraints

Where Does (2S,4R)-pNZ-Hydroxyproline Outperform the Corresponding N-Fmoc-analogue?