Tos-aminoxy-Boc-PEG4-Tos

This PROTAC linker, Tos-aminoxy-Boc-PEG4-Tos, is designed to provide a PEG-based, bis-activated scaffold that supports efficient conjugation of targeting ligands and subsequent formation of productive ternary complexes. Its ether-rich, flexible architecture can improve solubility and conformational adaptability, while protected functional groups enable controlled stepwise assembly. The sections below describe its structural features and practical reactivity considerations for constructing PROTACs.

Structure: Tos-aminoxy-Boc-PEG4-Tos contains a PEG-derived, flexible ether backbone with an N-tosyl/N-Boc-protected hydroxylamine at one end and an O-tosyl alkyl leaving group at the other. The protected hydroxylamine can be unmasked to provide an aminooxy group, while the opposite tosylate provides a separate substitution handle. Aromatic sulfonyl (tosyl) groups provide leaving-group behavior under appropriate conditions, while multiple ether linkages enhance polarity and hydration compatibility.

Reactivity: Suitable PROTAC assembly typically proceeds via selective functional-group transformations that preserve the PEG linker while installing or exchanging reactive handles on the warhead and E3 ligase ligand. The O-tosyl alkyl terminus can undergo nucleophilic substitution under base-promoted conditions, whereas the N-tosyl/N-Boc-protected hydroxylamine requires controlled deprotection before a free aminooxy group is available. Reaction planning should prioritize orthogonality, compatibility with sulfonate leaving groups, and solvent systems that maintain solubility and minimize linker degradation.