endo-BCN-PEG12-NHS ester

This endo-BCN-PEG12-NHS ester is a bifunctional PROTAC linker designed to enable efficient, modular assembly of targeted protein degraders. Its BCN (bicyclononyne) handle supports rapid strain-promoted click chemistry with azide-bearing partners, while the NHS ester provides a reactive acylating group for amide-bond formation. Together, these features facilitate controlled conjugation strategies that are widely used to build PROTAC architectures. Detailed structural and reactivity considerations are provided below.

Structure: The molecule contains an endo-BCN strained alkyne motif linked through a polyethylene glycol spacer to an N-hydroxysuccinimide ester. It features an activated carboxylate (NHS ester) for nucleophilic acyl substitution and a cyclooctyne-derived BCN for bioorthogonal cycloaddition. The PEG segment imparts hydrophilicity and conformational flexibility.

Reactivity: PROTAC construction typically uses two complementary steps: NHS ester acylation with primary amines to form stable amide bonds, followed by strain-promoted azide–BCN cycloaddition to connect remaining components without copper. Suitable conditions generally employ amine-containing nucleophiles in mildly basic aqueous or mixed solvents, then proceed to click coupling under conditions that preserve BCN integrity and minimize hydrolysis. No metal catalyst is required for BCN-based ligations, though buffer choice and pH control are important to limit NHS ester loss.