6-[6-[5-[(3aS,4S,6aR)-2-Oxohexahydro-1H-thieno[3,4-d]imidazol-4-yl]pentanamido]hexanamido]hexanoic Acid

This PROTAC linker is a carboxylic-acid–functionalized, multi-amide scaffold designed to connect targeting and E3-ligand moieties through robust amide-forming chemistry. Its polar, hydrogen-bonding–capable framework supports productive conjugation and can help tune linker length, conformational flexibility, and overall physicochemical properties relevant to targeted protein degradation. The detailed structural and reactivity considerations for constructing PROTACs with this linker are provided below.

Structure: The linker contains multiple amide linkages and a terminal carboxylic acid, incorporating a fused thieno-imidazolone motif within the overall framework. The structure features carbonyl-rich functional groups, amide N–H and heteroaromatic heteroatoms, enabling strong hydrogen bonding and stable covalent connectivity.

Reactivity: The terminal carboxylic acid is suitable for activation toward amide bond formation commonly used in PROTAC synthesis. Practical approaches include converting the acid to an activated ester or an acid chloride under standard coupling conditions, followed by nucleophilic acyl substitution with an appropriate amine-bearing partner. Mild base-mediated peptide-coupling strategies using coupling reagents and compatible solvents are typically employed to minimize side reactions and preserve sensitive heterocycles.