DBCO-NHCO-PEG4-NHS ester

This DBCO-NHCO-PEG4-NHS ester is a bifunctional PROTAC linker designed to couple a cyclooctyne (DBCO) handle with an NHS-activated ester for efficient attachment to amine-bearing ligands. Its PEG-based spacer enhances solubility and reduces steric constraints, supporting robust formation of PROTAC constructs. The orthogonal reactivity enables sequential, modular assembly of targeted degradation molecules. Detailed structural and reactivity considerations are provided below.

Structure: The linker contains a DBCO cyclooctyne moiety, a carbamate-linked amide segment, and a PEG spacer terminating in an NHS-activated ester. It features an NHS ester for nucleophilic acyl substitution and an alkyne-containing DBCO for strain-promoted cycloaddition, with multiple ether linkages contributing to hydrophilicity.

Reactivity: The NHS ester reacts with primary amines under mildly basic aqueous or mixed solvent conditions to form stable amide bonds via nucleophilic acyl substitution. The DBCO cyclooctyne undergoes strain-promoted azide–alkyne cycloaddition with azide-functional partners without added catalysts. For PROTAC assembly, prepare amine coupling first, then perform DBCO–azide ligation using compatible buffers that preserve NHS reactivity during the initial step and avoid azide/alkyne side reactions afterward.