Construction of Affinity Probes to Study the Epothilone Binding Site on Tubulin

The epothilones are 16-membered macrolides isolated from the myxobacteria, Sorangium cetlulosum. Their mode of action is microtubule hyperstabilization, which is shared with the anticancer drug paclitaxel. The epothilones have been the subject of synthetic and biological studies and this has resulted in clinical trials for several epothilone derivatives. In order to learn more about the epothilone binding site on tubulin we have targeted the synthesis of epothilone affinity probes. We have carried out tubulin labeling studies with two 12-hydroxylmethyl- derived arylazido epothilone analogues, however, no photoincorporation was observed. Studies toward the synthesis of an 8-hydroxymethyl analogue and a 4-hydroxyethyl epothilone derivative are at advanced stages of synthesis and will become available shortly for labeling studies. The chemistry procedures to obtain the various building blocks for the synthesis of the analogues has been validated, their synthesis has been scaled up, and the convergent assembly of the targeted molecules is underway.