Preparation of the membrane-permeant biarsenicals FlAsH-EDT2 and ReAsH-EDT2 for fluorescent labeling of tetracysteine-tagged proteins.

The membrane-permeant fluorogenic biarsenicals FlAsH-EDT(2) and ReAsH-EDT(2) can be prepared in good yields by a straightforward two-step procedure from the inexpensive precursor dyes fluorescein and resorufin, respectively. Handling of toxic reagents such as arsenic trichloride is minimized so the synthesis can be carried out in a typical chemistry laboratory, usually taking about 2-3 d. A wide range of other biarsenical reagents and intermediates that also bind to tetracysteine-tagged (CysCysProGlyCysCys) proteins can be prepared similarly using this general procedure.