Boc-gly-PEG3-endo-BCN

Boc-gly-PEG3-endo-BCN, is designed to connect protein-binding ligands through a PEG-based spacer while incorporating an endo-bicyclononyne (BCN) handle for bioorthogonal conjugation. Its flexible, hydrophilic architecture can improve solubility and reduce steric constraints in targeted protein degradation workflows. The BCN functionality enables efficient, catalyst-free ligation to azide-bearing partners, supporting modular PROTAC assembly. Detailed structural and reactivity considerations are provided below.

Structure: The linker contains a Boc-protected glycine unit connected to a short poly(ethylene glycol) spacer, terminating in an endo-bicyclononyne moiety. It features amide and carbamate linkages, ether-rich PEG segments, and a strained alkyne suitable for cycloaddition. Overall, it is expected to be water-compatible due to the PEG character.

Reactivity: Endo-BCN reacts with azides via strain-promoted azide–alkyne cycloaddition (SPAAC), typically under mild, aqueous-compatible conditions without added copper. For PROTAC construction, the linker is commonly coupled to azide-functional ligands or intermediates, then assembled into the final conjugate through SPAAC. Solvent systems that maintain ligand solubility and preserve BCN reactivity are preferred, and reaction progress is monitored by standard analytical methods.