Fmoc-NH-PEG6-NHS ester

Fmoc-NH-PEG6-NHS ester is a PEG-based, amine-reactive linker designed for constructing PROTACs and other targeted protein degradation conjugates. It combines an Fmoc-protected handle for controlled amide coupling with an NHS-activated ester that enables efficient formation of stable amide bonds with primary amines under mild conditions. This product offers convenient orthogonality for stepwise synthesis, improved solubility, and reduced steric bias, supporting reliable assembly of bifunctional degraders. Detailed structural and reactivity considerations are provided below.

Structure: The molecule features an Fmoc-protected nitrogen linked to a polyethylene glycol chain terminating in an NHS-activated carboxylate. It contains aromatic carbamate functionality, ether-rich PEG segments, and an activated N-hydroxysuccinimide ester for acyl transfer. Overall, it is an electrophilic, water-compatible linker with flexible, hydrophilic character.

Reactivity: The NHS ester typically reacts with primary amines to form amide bonds via nucleophilic acyl substitution. For PROTAC synthesis, amine-containing ligands are generally coupled in polar aprotic or buffered aqueous-organic media using base to maintain nucleophile availability while minimizing hydrolysis. No special catalysts are required; however, controlling exposure time and temperature helps preserve activation. After coupling, the Fmoc group can be deprotected under standard base conditions to enable subsequent conjugation steps.