Fluorescein-PEG6-bis-NHS ester
CAS No.: 2055105-59-2
Cat No.: BP-500400
Purity: 95%
4.5 
Fluorescein-PEG6-bis-NHS ester is a bifunctional, PEG-based linker that combines a fluorescein fluorophore with two N-hydroxysuccinimide (NHS) ester reactive groups at the termini of a six-unit polyethylene glycol chain. Structurally, it provides a flexible, hydrophilic spacer that reduces steric hindrance while enabling covalent conjugation to primary amines on proteins, peptides, or other targeting ligands via stable amide-bond formation. In PROTAC and targeted degradation workflows, such a linker is valuable for generating fluorescently traceable conjugates, for example by labeling E3 ligase recruiters or substrate-binding modules to monitor synthesis efficiency, cellular uptake, subcellular localization, and degradation kinetics. Its dual NHS functionality supports controlled, stoichiometric crosslinking or dual-labeling strategies, facilitating experimental optimization of multicomponent degraders and mechanistic studies of ternary complex formation and trafficking in biochemical and cell-based assays.
Structure of 2055105-59-2
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This Fluorescein-PEG6-bis-NHS ester is a bifunctional, fluorescent PROTAC linker building block designed to enable efficient conjugation of two ligands through NHS ester chemistry while providing optical tracking of assembly and cellular localization. Its PEG-based spacer imparts flexibility and solubility, and the fluorescein reporter facilitates monitoring of coupling efficiency and degradation workflows. The points below describe the structural features and practical reactivity considerations for constructing PROTACs using this reagent.
Structure: The molecule combines a fluorescein fluorophore with a flexible PEG spacer terminating in two activated N-hydroxysuccinimide (NHS) ester groups. It contains ester linkages on the terminal reactive sites, an ether-rich PEG backbone, and aromatic and xanthene-based ring systems. Overall, it is suited for aqueous bioconjugation due to PEG-mediated solvation and reduced steric congestion.
Reactivity: The bis-NHS ester reacts with primary amines via nucleophilic acyl substitution, forming stable amide bonds. Suitable conditions typically use mildly basic aqueous or mixed aqueous buffers to promote amine deprotonation while preserving NHS ester reactivity. Common coupling approaches include sequential or one-pot addition of amine-bearing ligands under controlled stoichiometry. No special catalysts are required; however, avoid prolonged exposure to water or competing nucleophiles (such as primary amines or excess buffers) to minimize hydrolysis.
* 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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