Aminooxy-PEG3-C2-thiol

Aminooxy-PEG3-C2-thiol is a bifunctional PEG-based linker designed for modular PROTAC construction, enabling efficient conjugation between thiol-bearing ligands and aminooxy-reactive partners. Its flexible poly(ethylene glycol) segment supports favorable linker conformations and can help mitigate steric constraints during target engagement. The thiol handle and aminooxy functionality make it well suited for chemoselective coupling strategies used to assemble targeted protein degraders. Detailed structural and reactivity considerations are provided below.

Structure: The linker contains an aminooxy group and a terminal thiol connected through a short PEG spacer and an ethylene (C2) segment. It features ether linkages within the PEG chain, a thio-functional end group, and an aminooxy moiety capable of forming stable oxime linkages under appropriate conditions.

Reactivity: PROTAC assembly can leverage chemoselective oxime ligation using the aminooxy functionality with aldehyde- or ketone-bearing ligands, typically under mildly acidic aqueous or mixed solvent conditions. The thiol end can be used for thiol–maleimide or thiol–disulfide exchange chemistries, depending on the electrophile present on the partner ligand. Common approaches employ buffered solvents and freshly prepared thiol reagents to maintain nucleophilicity and minimize oxidation.