Fluorescent and photoaffinity labeling derivatives of rhizoxin

A fluorescent probe (D-RZX) and a photoreactive fluorescent probe (AD-RZX) for studying the rhizoxin binding site on tubulin were prepared by the derivatization of rhizoxin (RZX). D-RZX consists of a rhizoxin moiety and a dansyl moiety. AD-RZX has a 5-azidonaphthalene-1-sulfonyl moiety instead of the dansyl moiety of D-RZX. Both D-RZX and AD-RZX bound tubulin in a mutually competitive manner with rhizoxin, indicating their binding to the rhizoxin site on tubulin. AD-RZX bound the rhizoxin site covalently after UV-irradiation, thus showing its usefulness as a photo-affinity probe for labeling of the rhizoxin site.