Biotin-PEG6-NH-Mal

This Biotin-PEG6-NH-Mal linker is designed for constructing PROTACs that incorporate a biotin handle and a maleimide electrophile for efficient, chemoselective conjugation. Its PEG-based spacer supports favorable solubility and flexible presentation of functional groups, while the maleimide enables stable thioether formation with thiol-bearing ligands. These features make the linker well suited for targeted protein degradation workflows, where modular assembly and reliable linker–warhead coupling are critical. Detailed structural and reactivity considerations are provided below.

Structure: The linker contains a biotin moiety connected through a polyethylene glycol spacer, terminating in a maleimide functionality. It features amide and ether linkages within the PEG chain and a maleimide ring capable of Michael-type addition. Overall, it is a polar, water-compatible scaffold with an electrophilic double bond.

Reactivity: The maleimide group is reactive toward free thiols via a chemoselective Michael addition, typically forming a thioether under mildly basic aqueous conditions. For PROTAC assembly, thiolated ligands or cysteine-containing components can be coupled to the maleimide-bearing linker to generate stable conjugates. Common approaches use buffered aqueous solvents with controlled pH and temperature, avoiding strong nucleophiles and conditions that promote maleimide hydrolysis.