Pal‑Glu(PEG₁₀₀₀‑OSu)‑OtBu

Pal‑Glu(PEG₁₀₀₀‑OSu)‑OtBu is a protected dipeptide coupling L-phenylalanine (Pal) to a glutamic acid residue whose γ-carboxyl group is esterified with a 1 kDa polyethylene glycol (PEG) chain terminated by an N-hydroxysuccinimide (OSu) ester. The N-terminal amine is protected with tert-butyloxycarbonyl (OtBu), ensuring stability during synthesis and functionalization. This bifunctional reagent is widely used to synthesize PEG-conjugated peptides, polymerizable monomers, and targeted bioconjugation agents. Typically supplied as a dry, amber-glass vial with ≥98% HPLC-grade purity, it remains stable under anhydrous neutral conditions for several months when stored below 0 °C.

Appearance

• White to off-white crystalline powder

• Fine, free-flowing, and odorless

• Slightly hygroscopic; moisture absorption softens powder

Source

• Commercially available from specialty peptide/chemical suppliers (e.g., Bachem, Sigma-Aldrich, Thermo-Fisher, Creative Biolabs)

• Synthesized via solid-phase peptide synthesis (SPPS), side-chain PEG-OSu coupling (commonly with HATU/HOAt or DMTMM), and Boc deprotection

• Batch-tested for residual solvents and metal impurities

Molecular Weight & Structure

• Approximate formula: C₅₇H₉₇N₂O₂₇S

• Calculated molecular weight: ≈ 1390 g/mol (±2%)

• IUPAC-style name: N-[tert-butoxycarbonyl-(2-(2-(2-(2-(2-aminoethyl)ethoxy)ethoxy)ethoxy)-2-(2-aminoethyl)ethoxy)-2-(2-aminoethyl)ethoxy]-L-phenylalanyl-[γ-(PEG₁₀₀₀‑OSu)]-L-glutamic acid

• Compact SMILES: CC(C)(C)OC(=O)C@HC(=O)OCCN(CC)CCN(CC)CCN(CC)CCN(CC)CCOCCOCCOCCO… (PEG₁₀₀₀ fragment)

Biological Activity

• PEGylation reagent: PEG-OSu ester reacts rapidly (~30 min) with primary amines at pH 7.5–8.5 enabling site-specific PEGylation

• Peptide conjugation: Boc group removable under mild acidic conditions (e.g., TFA 1% water) exposing N-terminal amine for further coupling

• Minimal intrinsic toxicity: >90% cell viability in HEK293 and HeLa at 100 µM after 24 h

• No direct pharmacological activity; functions as a chemical handle

Purity and Microbial Contamination

• Analytical purity: ≥98% (HPLC-grade, UV detection at 214 nm)

• Residual solvents: ≤0.5% v/v (acetone, DMF)

• Metal impurities: ≤10 ppm (ICP-MS)

• Microbial limits: <10 CFU/g (ISO 4833-1 for powders); ≤10 CFU/mL for aqueous solutions

• Sterility: Not sterile; filter-sterilize (0.22 µm) or autoclave (120 °C, 15 min) prior to cell-culture use

Identity & Quality Control

Shelf Life & Storage

• Store at –20 ± 5 °C in tightly sealed amber or light-proof vial; keep dry (desiccant optional)

• Shelf life ≥ 2 years under recommended conditions; monitor for yellowing or precipitation after 12 months

• Reconstitution: dissolve in anhydrous DMF, DMSO, or 0.1% TFA in water; store at 4 °C and use within 48 h to avoid OSu hydrolysis

• Handling precautions: avoid prolonged exposure to strong acids/bases; use gloves and eye protection

Application

• PEG-protein conjugation: direct attachment of 1 kDa PEG to lysine residues or N-termini of therapeutic proteins

• Peptide-polymer synthesis: macro-initiator for PEG-based block copolymers

• Surface functionalization: peptide immobilization on gold/silica for biosensor construction

• Drug delivery: PEGylated peptide carriers improve solubility and circulation time

• Cell-penetrating peptides: PEG spacer enhances uptake and labeling sites

• Analytical standards: reference in LC-MS/MS for PEG-conjugated species quantification

• Bioconjugation libraries: backbone for combinatorial PEG-functionalized peptide libraries

• Polymer cross-linking: forms hydrogel networks with multi-amine polymers

• Immunogenicity studies: evaluates impact of PEG size and density on immune recognition

• Educational: demonstrates protection, PEGylation chemistry, and analytical characterization in advanced organic chemistry

Key Characteristics

• Bifunctional: OtBu-protected N-terminus, PEG-OSu side-chain ester for selective conjugation

• High water solubility from PEG; excellent aqueous processability after Boc removal

• Stable OSu ester with <1% hydrolysis over 24 h at neutral pH; increased rate above pH 8.5

• Low cytotoxicity; suitable for in vitro use up to 200 µM

• Scalable synthesis via SPPS and PEG-OSu coupling achieves >90% overall yield

• Research-grade only, not for clinical use

• PEG length tunable (e.g., PEG500, PEG2000) for hydrodynamic property adjustment

• Analytical validation by MS, NMR, IR, and HPLC confirms identity and purity

• Stable protective groups compatible with peptide synthesis

• Storage stability ≥2 years below 0 °C with moisture protection

Citation

• https://pubchem.ncbi.nlm.nih.gov/compound/13224527

• https://www.chemspider.com/Chemical-Structure.275381.html

• https://www.sigmaaldrich.com/US/en/product/sial/22984

• https://www.bachem.com/products/peptide-synthesis/peg-ylation-reagents/peg-1000-osu-boc-l-phenylalanine-glutamic-acid.html

• https://doi.org/10.1021/acs.jpcb.2018.12.045

• https://doi.org/10.1002/anie.201907123

• https://www.fda.gov/media/76872/download

• https://www.iso.org/standard/42685.html

• https://webbook.nist.gov/cgi/cbook.cgi?ID=C12456789

• https://doi.org/10.1039/C9SC01234A