Amino-PEG2-t-butyl ester

This amino-PEG2-t-butyl ester linker is designed for modular PROTAC synthesis, providing a flexible polyethylene glycol spacer that can improve effective spatial reach between the target-binding ligand and the E3 ligase-recruiting moiety. The t-butyl ester functionality enables controlled installation and subsequent conversion to a reactive carboxylate handle under mild deprotection conditions, facilitating efficient conjugation workflows. The detailed structural and reactivity considerations are provided below.

Structure: The linker contains an amino group and a short polyethylene glycol segment, terminating in a t-butyl ester. It features ether linkages within the PEG chain, an amide-adjacent functional motif depending on conjugation state, and a tert-butyl ester that is acid-labile. Overall polarity and hydrogen-bonding capacity support solubility and linker flexibility.

Reactivity: The t-butyl ester can be converted to the corresponding carboxylic acid under acid-mediated deprotection, generating a carboxylate suitable for amide bond formation. For PROTAC assembly, the resulting acid is commonly coupled to amine-bearing ligands using standard peptide-coupling strategies (e.g., carbodiimide-based systems with additives) in polar aprotic solvents. Alternatively, the amino functionality can be used for coupling to activated carboxyl derivatives, proceeding via nucleophilic acyl substitution.