Fluorescein-thiourea-PEG4-azide
CAS No.: 1454662-54-4
Cat No.: BP-500544
Purity: 95%
4.5 
Fluorescein-thiourea-PEG4-azide is a multifunctional PROTAC linker building block that combines a fluorescein fluorophore with a thiourea-based connection motif and a four-unit polyethylene glycol (PEG) spacer terminating in an azide handle. Structurally, the thiourea linkage provides a stable conjugation element, while the PEG segment confers hydrophilicity and conformational flexibility that can reduce steric interference between the two PROTAC-relevant domains. In targeted protein degradation workflows, the azide group enables bioorthogonal “click” conjugation to complementary alkyne-bearing partners, allowing researchers to attach fluorescent or affinity-modulating modules without disrupting the core binding pharmacophores. The fluorescein functionality is particularly valuable for monitoring synthesis efficiency, tracking cellular uptake or localization, and quantifying conjugate formation in degradation assays. This reagent therefore supports rigorous experimental design and characterization of linker-dependent effects on PROTAC performance, including assembly, stability, and intracellular behavior.
Structure of 1454662-54-4
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Fluorescein-thiourea-PEG4-azide is a versatile PROTAC linker component that integrates a fluorescent fluorescein handle with a thiourea-based connectivity motif and a PEG-based spacer terminating in an azide for bioorthogonal conjugation. Its combination enables efficient assembly of targeted protein degraders while supporting downstream visualization and tracking of linker incorporation. The structural and synthetic considerations that govern its use in PROTAC construction are described in detail below.
Structure: The linker contains a fluorescein fluorophore, a thiourea linkage, and a poly(ethylene glycol) spacer that enhances solubility and conformational flexibility. It features an azide functional group suitable for click-type coupling, along with aromatic and heteroatom-rich domains that support strong electronic and hydrogen-bonding interactions.
Reactivity: The azide terminus is designed for copper-catalyzed azide–alkyne cycloaddition or related azide-compatible conjugation strategies commonly used in PROTAC assembly. Linker incorporation typically proceeds via formation of a stable triazole linkage under mild aqueous or mixed-solvent conditions, with appropriate base and ligand/catalyst systems to control reaction rate and minimize fluorophore quenching. Thiourea functionality can participate in hydrogen-bonding during synthesis and may influence coupling efficiency and final solubility.
* 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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