page_title: FlAsH-EDT2
section_title: Preparation
hierarchical_section_title: FlAsH-EDT2 / Preparation
caption_attribution_description: English: FlAsH preparation
context_page_description: FlAsH-EDT₂ is an organoarsenic compound with molecular formula C₂₄H₁₈As₂O₅S₄. Its structure is based around a fluorescein core with two 1,3,2-dithiarsolane substituents. It is used in bioanalytical research as a fluorescent label for visualising proteins in living cells. FlAsH-EDT₂ is an abbreviation for fluorescin arsenical hairpin binder-ethanedithiol, and is a pale yellow or pinkish fluorogenic solid. It has a semi-structural formula (C₂H₄AsS₂)₂--C₆H₄COOH, representing the dithiarsolane substituents bound to the hydroxyxanthone core, attached to an o-substituted molecule of benzoic acid.
  FlAsH-EDT₂ is used for site-specific labelling, selectively binding to proteins containing the tetracysteine motif Cys-Cys-Xxx-Xxx-Cys-Cys and becoming fluorescent when bound. It displays non-specific binding to endogenous cysteine-rich proteins, meaning it binds to sites other than the one of interest. Further optimization of the TC motif has revealed improved FlAsH binding affinity for a CCPGCC motif, and higher quantum yield when the tetracysteine motif is flanked with specific residues.
context_section_description: FlAsH-EDT₂ can be prepared in three steps from fluorescein (see figure).
caption: Step 1: HgO in TFA; Step 2: AsCl3, followed by Pd(OAc)2 and DIEA; Step 3: H2EDT in aqueous acetone.
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