Chemical Structure and Molecular Design

(S)-2,6-Bis-(m-PEG8)-amidohexanoic acid is built on an L-lysine-derived hexanoic acid scaffold in which both the alpha (2-position) and epsilon (6-position) amino groups have been acylated with methoxy-terminated octaethylene glycol (m-PEG8) chains, yielding a symmetric bis-amide architecture. The molecule retains a single free carboxylic acid at the 1-position, serving as the primary reactive handle for downstream conjugation to amines, alcohols, or other nucleophiles via standard coupling chemistry such as EDC/NHS activation.

The stereochemical center at C-2 is maintained in the (S) configuration, corresponding to the natural L-amino acid absolute configuration. This chirality can be important in biological contexts where stereoselectivity of enzymatic processing or receptor interaction is considered. The two m-PEG8 arms each contribute eight ethylene oxide repeat units, providing a combined PEG mass contribution that substantially increases the hydrodynamic radius and aqueous solubility of any molecule to which this building block is attached.

Physicochemical Properties and Handling

The bis-m-PEG8 substitution pattern confers excellent hydrophilicity to this building block. PEG chains of this length are well documented to coordinate water molecules through hydrogen bonding with ether oxygens, resulting in a highly water-soluble compound suitable for aqueous buffer systems commonly used in bioconjugation workflows. The methoxy end-caps prevent undesirable chain-end reactivity and ensure chemical stability under standard laboratory conditions.

The amide bonds linking the PEG chains to the lysine backbone are stable across a broad pH range and are resistant to hydrolysis under physiological conditions, making the compound suitable for applications that require metabolic or physiological stability. The free carboxylic acid terminus has a pKa consistent with aliphatic carboxylic acids (approximately 2–4), and is readily activated using carbodiimide-based or other standard coupling reagents.

For handling, the compound should be stored according to supplier recommendations, typically at low temperature and protected from moisture to prevent hygroscopic uptake by the PEG chains. Solutions should be prepared fresh or stored at –20 °C in aliquots to maintain integrity. Compatibility with common organic co-solvents such as DMSO and DMF broadens its utility in mixed aqueous-organic reaction systems.

Research Applications and Use Cases

(S)-2,6-Bis-(m-PEG8)-amidohexanoic acid is primarily used as a PEG-based solubility and pharmacokinetic modifier in medicinal chemistry and chemical biology research. Its bis-PEGylated architecture enables researchers to append two hydrophilic PEG chains to a single attachment point on a molecule of interest via the carboxylic acid handle, effectively increasing aqueous solubility, reducing aggregation, and potentially extending plasma half-life in preclinical studies.

Key application areas include: (1) PROTAC and targeted protein degradation — as a hydrophilic linker component that improves aqueous solubility of otherwise lipophilic bifunctional degrader molecules; (2) antibody-drug conjugate (ADC) linker chemistry — as a building block to introduce PEG spacers that reduce aggregation of hydrophobic payloads; (3) peptide and small-molecule PEGylation — to modify bioactive molecules and improve their developability profiles; and (4) probe and tool compound synthesis — where solubility enhancement is required for cellular or biochemical assay compatibility.

The free carboxylic acid allows straightforward coupling to primary amines on peptides, proteins, or small molecules using standard NHS ester or carbodiimide chemistry, making this reagent broadly accessible to researchers without specialized conjugation infrastructure.

Ordering and Product Specifications

(S)-2,6-Bis-(m-PEG8)-amidohexanoic acid is available from Aladdin Scientific under catalog number B596788. This product is cross-referenced to BroadPharm catalog number BP-24221. Researchers are advised to confirm current available pack sizes, purity specifications, and certificate of analysis data directly with Aladdin Scientific at the time of ordering, as these parameters may be updated.

For procurement, laboratory managers should verify the structural confirmation data (e.g., NMR, MS) provided in the certificate of analysis to ensure the compound meets the purity requirements of their specific application, particularly for sensitive assays such as PROTAC cell viability studies or quantitative bioconjugation reactions.