Hydroxy-PEG9-t-butyl ester
CAS No.: 2055042-66-3
Cat No.: BP-501096
Purity: ≥95%
4.5 
Hydroxy-PEG9-t-butyl ester is a polyethylene glycol (PEG) linker featuring a terminal hydroxyl group and a protected carboxyl functionality masked as a tert-butyl ester. Structurally, it provides a flexible, hydrophilic chain of moderate length that can be used to spatially separate a ligand-binding moiety from a second functional component while reducing steric clashes and improving aqueous solubility. In PROTAC and targeted protein degradation design, this type of linker is commonly employed to connect two “warheads” (for example, an E3 ligase ligand and a target-binding ligand) through orthogonal chemistries, with the hydroxyl serving as a handle for further derivatization and the tert-butyl ester enabling controlled activation or downstream coupling strategies. The PEG architecture can also help tune the effective geometry required for productive ternary complex formation. This product is therefore valuable for systematic linker optimization in degradation experiments, supporting reproducible conjugate synthesis and facilitating structure–activity relationship studies.
Structure of 2055042-66-3
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Hydroxy-PEG9-t-butyl ester is a polyethylene glycol-based PROTAC linker designed to provide solubility, conformational flexibility, and efficient spacing between a targeting ligand and an E3-recruiting module. Its hydroxy functionality enables orthogonal coupling strategies, while the t-butyl ester offers a protected carboxyl handle that can be unmasked under mild deprotection conditions. These features make it well suited for constructing degraders where controlled linker length and reliable attachment chemistry are critical; detailed structural and reactivity considerations follow below.
Structure: The linker comprises an ether-rich PEG backbone bearing a terminal hydroxy group and a carboxyl protected as a t-butyl ester. It contains multiple C–O–C ether linkages, a stable ester linkage, and a hydroxyl group that supports further derivatization. The PEG segment confers hydrophilicity and flexibility, improving aqueous handling and conjugation compatibility.
Reactivity: The hydroxy group is compatible with common functionalization routes such as esterification, ether formation, or coupling to activated electrophiles used in PROTAC assembly. The t-butyl ester can be cleaved via acid-mediated deprotection to generate a free carboxylic acid for subsequent amide or ester bond formation. Typical workflows use anhydrous organic solvents for coupling steps, followed by controlled deprotection and purification to preserve linker integrity and minimize side reactions.
* 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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