Epothilone A and B—Novel 16‐Membered Macrolides with Cytotoxic Activity: Isolation, Crystal Structure, and Conformation in Solution

How similar must a compound be to taxol in order to displace it from its binding site on microtubules? The microbial secondary metabolites epothilones A (1a) and B (1b) provide an answer to this question. These comparatively small, simply constructed, and highly cytotoxic macrolides surprisingly show no similarity to taxol, according to X-ray and NMR spectroscopic results.