Azido-PEG3-amine: A Heterobifunctional PEG Linker Bearing an Amine and an Azide Terminus

Basic Information

(1) Product name: Azido-PEG3-amine

(2) Structural abbreviation: N3–PEG3–NH2

(3) CAS No.: 134179-38-7

(4) Aladdin catalog Nos.: A122192 ≥98%

Azido-PEG3-amine is a typical heterobifunctional PEG linker, bearing an azide group (–N3) and a primary amine (–NH2) at opposite termini, connected by a triethylene glycol (PEG3) spacer segment in between.

Structural Features

From a structural perspective, the IUPAC name of this linker is 1-amino-11-azido-3,6,9-trioxaundecane, corresponding to the molecular formula C₈H₁₈N₄O₃ (8 carbon atoms). The linear structure, from the amino terminus to the azido terminus, can be written as:

NH₂–CH₂–CH₂–O–CH₂–CH₂–O–CH₂–CH₂–O–CH₂–CH₂–N₃

(1) The blue segment represents the aminoethyl terminus (amine + two-carbon arm), which primarily reacts with carboxylic acids, NHS esters and aldehydes/ketones, serving as the “starting point” for conjugation.

(2) The green segment represents the PEG3 spacer, composed of three consecutive –O–CH₂–CH₂– units. It imparts hydrophilicity and flexibility, improves the overall aqueous solubility of the molecule, and acts as a “spacer arm” after conjugation to reduce steric hindrance.

(3) The red segment represents the azidoethyl terminus, which serves as the reactive site for CuAAC/SPAAC click chemistry with alkynes, BCN, DBCO and related partners, forming stable triazole linkages.

This “blue aminoethyl terminus + green PEG3 spacer + red azidoethyl terminus” structural design endows Azido-PEG3-amine with both excellent aqueous solubility and programmable reactivity at both ends, making it a highly practical linker for bioconjugation and materials surface modification.

Physicochemical and Solubility Properties

(a) Typically appears as a colorless to pale yellow liquid or oily solid, with an appearance characteristic of PEG-based materials.

(b) Owing to the presence of a PEG chain and a terminal amine, it shows good solubility in polar solvents such as water, methanol and DMSO.

(c) The azide group is generally stable under standard storage conditions; however, exposure to elevated temperatures and strongly reducing environments should be avoided.

Bifunctional Reactivity

Reactivity of the amine terminus (–NH2)

The amine terminus is a typical primary amine and can form covalent bonds with a variety of functional groups, most commonly:

1. Reaction with carboxylic acids / activated carboxylic acids (e.g., NHS esters)

(a) In the presence of water-soluble coupling reagents or activators (such as EDC/NHS), the amine can react with carboxyl groups on molecules or material surfaces to form stable amide bonds.

(b) This represents one of the most common applications of Azido-PEG3-amine:

(i) Conjugation to carboxyl-containing small molecules, dyes and biomolecules (such as peptides and proteins);

(ii) Surface modification of carboxyl-functionalized nanoparticles, polymeric materials and coatings.

2. Reaction with aldehydes and ketones (Schiff base formation)

(a) The amine can condense with aldehydes or ketones to form imine (Schiff base) intermediates.

(b) Upon addition of a mild reducing agent (such as NaBH3CN), these intermediates can be further reduced to more stable C–N bonds.

(c) This strategy is frequently used for mild conjugation to aldehyde-containing polysaccharides, glycoproteins and related biomolecules.

Click chemistry at the azide terminus (–N3)

The azide group is one of the most important functional motifs in click chemistry:

1. Cu(I)-catalyzed azide–alkyne cycloaddition (CuAAC)

(a) The azide can undergo a 1,3-dipolar cycloaddition with terminal alkynes (–C≡CH) under Cu(I) catalysis.

(b) This reaction affords structurally robust 1,2,3-triazole rings, which generally exhibit excellent chemical and biological stability.

(c) It is one of the classic reactions in click chemistry.

2. Copper-free click reaction (SPAAC) with BCN, DBCO and other strained alkynes

(a) Strained cyclic alkynes such as BCN and DBCO can react directly with azides under metal-free conditions.

(b) These reactions are suitable for systems that are sensitive to metal ions, such as live-cell labeling and the construction of bioimaging probes.

Through these reactions, the azide terminus of Azido-PEG3-amine can be “clicked” onto a wide range of fluorescent dyes, drug molecules, probes and surface ligands, forming stable triazole linkages.

Typical Application Scenarios

1. Dual labeling / crosslinking of biomolecules

(a) The amino terminus is first coupled to carboxyl-containing biomolecules (such as peptides or proteins), and the azide terminus is subsequently subjected to click chemistry with alkyne-functionalized fluorophores or drug molecules.

(b) This yields “biomolecule–PEG–functional molecule” architectures that can be used for imaging, targeting, or functional studies.

2. Nanomaterials and surface modification

(a) The amino terminus can be used to attach Azido-PEG3-amine to the surface of nanoparticles bearing carboxyl groups or activated esters (e.g., polylactic acid nanoparticles, polymer microspheres).

(b) The azide terminus is then employed in click reactions to introduce various hydrophilic ligands or cell-targeting moieties, thereby tuning the biocompatibility and targeting properties of the nanomaterials.

3. Flexible linker for small-molecule drugs or probes

(a) Azido-PEG3-amine can serve as a flexible PEG linker, enabling small-molecule drugs or probes to be connected via its two termini to carriers or other functional modules.

(b) The PEG segment helps enhance overall aqueous solubility, reduce steric hindrance, and, to some extent, improve in vivo distribution profiles.

In such designs, the central PEG3 segment provides the necessary flexibility and hydrophilicity, while the terminal amine and azide groups are used for different types of conjugation reactions, respectively.

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