Propargyl-PEG4-tetra-Ac-beta-D-galactose

Propargyl-PEG4-tetra-Ac-beta-D-galactose is a polyethylene glycol (PEG)-based PROTAC linker building block designed to connect targeting ligands to E3-recruiting or warhead modules while enhancing aqueous solubility and improving linker flexibility. Its propargyl functionality supports efficient conjugation, and the galactose-derived tetra-acetate motif provides a defined carbohydrate handle for controlled attachment strategies. The detailed Structure and Reactivity parameters below describe its chemical characteristics and practical use in PROTAC assembly.

Structure: The linker contains a PEG chain providing conformational flexibility, terminated by a propargyl (alkyne) group for bioorthogonal-style coupling. A beta-D-galactose core bearing multiple acetate esters contributes defined stereochemistry and increased hydrophobicity relative to the free sugar. Ether and ester linkages dominate its connectivity.

Reactivity: The terminal alkyne enables conjugation via copper-catalyzed azide–alkyne cycloaddition or related alkyne-based coupling approaches commonly used for PROTAC construction. Typical conditions employ a compatible solvent system and a copper catalyst with appropriate ligand stabilization to minimize side reactions. Reaction efficiency depends on maintaining mild temperatures, controlling oxygen exposure, and ensuring functional-group compatibility with sensitive targeting ligands and E3-binding moieties.