Phosphonic acid,1,4-butanediylbis-, tetraethyl ester (9CI)
CAS No.: 7203-67-0
Cat No.: BP-500514
4.5 
Phosphonic acid, 1,4-butanediylbis-, tetraethyl ester (often described as a bis-phosphonate tetraethyl ester) is a symmetrical linker featuring a four-carbon spacer between two phosphonate termini, with each phosphonate masked as an ethyl ester. This structural motif provides a compact, chemically stable connection point that can be incorporated into PROTAC architectures where phosphonate-bearing fragments are advantageous for controlled geometry and for tuning polarity and solubility of the conjugate. In targeted protein degradation designs, such linkers can serve as rigid or semi-rigid spacers that position the two binding modules (e.g., an E3 ligase ligand and a target-binding ligand) to favor productive ternary complex formation, while the phosphonate functionality offers a handle for subsequent deprotection or derivatization to enable specific coupling strategies. The compound is therefore valuable for researchers developing linker libraries, optimizing linker length/rigidity, and improving experimental tractability during PROTAC synthesis and structure–activity relationship studies.
Structure of 7203-67-0
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This phosphonate linker is designed to serve as a robust, hydrolytically stable connection element in targeted protein degradation (PROTAC) architectures. Its tetraethyl phosphonate functionality provides a versatile handle for constructing stable conjugates that support controlled spatial organization between the ligand-recruiting modules. The linker’s chemical features can help maintain linker integrity under typical PROTAC synthesis conditions, enabling reproducible assembly and downstream evaluation. Detailed structural and reactivity considerations are provided below.
Structure: The material is a bis-phosphonate ester featuring a butane-1,4-diyl spacer and two phosphonic acid-derived tetraethyl ester groups. It contains P–O and P–C connectivity with multiple ester linkages, providing a compact, polarizable scaffold. The presence of phosphonate esters imparts characteristic acidity upon activation and strong coordination potential.
Reactivity: For PROTAC construction, tetraethyl phosphonate linkers are commonly employed via ester activation or transformation to enable coupling to ligand-bearing functional groups. Typical approaches include hydrolysis to the corresponding phosphonic acid followed by conversion to an activated intermediate suitable for amide or other bond-forming strategies, or direct use of phosphonate-derived electrophiles where compatible. Mild base or acid conditions are selected to preserve sensitive ligand motifs, using standard organic solvents and inert atmosphere when required by functional group stability.
* Our calculator is based on the following equation:
Concentration (start) x Volume (start) = Concentration (final) x Volume (final)
It is commonly abbreviated as: C1V1 = C2V2
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