Fluorescein-PEG5-NHS ester
CAS No.: 2353409-62-6
Cat No.: BP-501570
Purity: 95%
4.5 
Fluorescein-PEG5-NHS ester is a fluorescent, PEG-based linker that combines a fluorescein dye with a short, flexible polyethylene glycol spacer terminated by an N-hydroxysuccinimide (NHS) ester. The PEG5 chain provides aqueous solubility and spatial separation between the dye and the reactive group, while the NHS ester enables efficient, amide-bond formation with primary amines on proteins, peptides, or other amine-containing handles under standard bioconjugation conditions. In PROTAC and targeted protein degradation workflows, this reagent is valuable for installing a traceable fluorophore onto lysine-containing ligands or other amine-functionalized components, facilitating monitoring of conjugation efficiency, quantifying labeling stoichiometry, and tracking material behavior during synthesis and purification. Its compact PEG spacer helps preserve the functional accessibility of the conjugated partner, supporting rigorous experimental validation of PROTAC assembly and downstream biochemical assays.
Structure of 2353409-62-6
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Fluorescein-PEG5-NHS ester is a fluorescent polyethylene glycol (PEG) linker designed for efficient conjugation chemistry in PROTAC workflows, enabling attachment of targeting ligands or handles while providing strong optical readouts for monitoring synthesis and ternary complex formation. Its NHS-ester functionality supports rapid, mild coupling, and the PEG spacer enhances solubility and spatial separation to reduce steric interference. The sections below describe the linker’s structure and practical reactivity for constructing PROTAC conjugates.
Structure: The linker combines a fluorescein fluorophore with a PEG chain terminated by an N-hydroxysuccinimide ester. It contains an activated carboxylate (NHS ester) for nucleophilic acyl substitution, multiple ether linkages in the PEG segment, and aromatic xanthene-derived fluorescence-bearing motifs.
Reactivity: The NHS ester reacts with primary amines and, in some cases, amino-functional groups on ligands under mildly basic aqueous or mixed solvent conditions. Formation proceeds via nucleophilic acyl substitution, releasing N-hydroxysuccinimide. Typical approaches use buffered solutions and avoid prolonged exposure to strong nucleophiles that can hydrolyze the ester; catalysts are generally unnecessary, while careful control of pH and water content helps maintain coupling efficiency.
* 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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