Synthesis of Reblastatin, Autolytimycin, and Non-Benzoquinone Analogues: Potent Inhibitors of Heat Shock Protein 90

A full account of an asymmetric synthesis of reblastatin (1) and the first total synthesis of autolytimycin (2) and related structural compounds is described. The syntheses expand the utility of a highly regio- and diastereoselective hydrometalation aldehyde addition sequence to assemble the fully functionalized ansa chain of the natural products. Also documented is an intramolecular copper-mediated amidation reaction to close the 19-membered macrolactams. The amidation reaction was also employed for the generation of structural derivatives (6-9) of phenolic ansamycins. Ansamycin natural products and selected structural analogues were evaluated in a competitive binding assay to breast cancer cell lysate and a cytotoxicity assay. Both reblastatin (1) and autolytimycin (2) were shown to bind the heat shock protein 90 with enhanced binding activity (similar to 25 nM) than 17-allylamino-17-demethoxygeldanamycin (17-AAG, 4), a geldanamycin (3) derivative currently under evaluation for treatment of cancer (similar to 100 nM).