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A full account of an asymmetric synthesis of reblastatin (1), 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 analogs 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 Hsp90 protein with enhanced binding activity (~25 nM) than 17-allylamino-17-demethoxygeldanamycin (17-AAG, 4), a geldanamycin (3) derivative currently under evaluation for treatment of cancer (~100 nM).

Enantioselective total synthesis of reblastatin is described. The synthesis highlights hydrozirconation, transmetalation, aldehyde addition sequence to install E-trisubstituted olefin and C7 stereocenter, and the first use of an intramolecular Buchwald-like amidation reaction to close the 19-membered macrolactam.

Ansamycin antibiotics are a class of microbial metabolites that exhibit an array of biological activities. This review covers the synthetic chemistry and biological activity of benzenic ansamycins from 1989 to 2007. In the first section, synthetic approaches to the C15-benzene ansamycins (geldanamycin and related) are discussed. Access to the C17-benzene ansamycins (or ansatrienins) is disclosed in the second half of this article.