Fluorescein-PEG4-acid
CAS No.: 1807518-76-8
Cat No.: BP-500817
Purity: 96%
4.5 
Fluorescein-PEG4-acid is a fluorescein-based linker featuring a short polyethylene glycol spacer (four ethylene glycol units) terminated with a carboxylic acid. The PEG segment provides hydrophilicity and conformational flexibility, helping to reduce steric interference when the fluorophore is conjugated to other PROTAC components. In targeted protein degradation workflows, such linkers are commonly used to generate fluorescently traceable PROTACs or PROTAC-related probes, enabling visualization of cellular uptake, intracellular localization, and trafficking of the assembled degraders. The terminal carboxyl group supports covalent attachment to amine- or hydrazide-bearing partners via standard coupling chemistries, allowing researchers to position the dye at a defined distance from the binding moieties. This product is valuable for mechanistic studies, including monitoring compound distribution and optimizing linker length and attachment sites to improve degradation efficiency and experimental reproducibility.
Structure of 1807518-76-8
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Fluorescein-PEG4-acid is a PEG-based linker building block designed to support PROTAC architectures that benefit from enhanced solubility, flexible spacing, and reliable conjugation handles. Its hydrophilic PEG segment can improve bioconjugate presentation and reduce steric constraints between the targeting ligand and the E3-recruiting module. The fluorescein-containing scaffold further enables fluorescence-based monitoring of synthesis and, where applicable, assay workflows.
Structure: This linker combines a fluorescein chromophore with a PEG spacer terminated by a carboxylic acid. It features ether linkages within the PEG chain, an aromatic xanthene core, and a terminal carboxyl group suitable for amide coupling. Overall, it is amphiphilic and water-compatible due to the PEG segment.
Reactivity: The carboxylic acid functionality is typically used for PROTAC linker attachment via amide bond formation. Common approaches include activating the acid with carbodiimide coupling reagents and an auxiliary base, followed by reaction with an appropriate amine-bearing partner under mild aqueous-organic conditions. Alternatively, acid-to-ester or acid-to-activated ester intermediates can be employed to control chemoselectivity. Reaction outcomes depend on pH, reagent stoichiometry, and protection of other nucleophilic groups.
* 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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