Synthesis and Early Assessment of Epothilone-Derived Fluorescent Probes for Microtubule Imaging

The synthesis of two bright epothilone-based fluorescent probes for microtubule imaging is described. Building on a tested strategy for the synthesis of epothilone-type structures, an analog of epothilone B with an extended C(6) substituent terminating in an alkyne group has been prepared. A Huisgen [3 + 2] cycloaddition of this analog with azide-functionalized derivatives of Alexa Fluor 488 and Janelia Fluor 646 gave bright fluorescent probes emitting in the green and far-red spectral range, respectively. Both probes bind to microtubules with high affinity and specifically label the microtubule network in A549 cells.