Preparation of the Three C1-C7, C8-C15, and C16-N22 Fragments of the Hsp90 Inhibitor Herbimycin A

The construction of the three C16-N22 2, C1-C7 6 (as 23) and C8-C15 5 (as 32) segments of the Hsp90 inhibitor herbimycin A (1) is reported. 1Iodo-3-nitro-2,5-diphenol compound 2 was obtained in 55% yield for 3 steps from the commercially available diiodo derivative 7. Reaction between 1,1-dibromo-alkene 22 and vinyltin 17a using Pd(PPh3)4 or Pd(CH3CN)2Cl2/CuI/diisopropylethylamine, in toluene or DMF at 85 °C, led to enyne 23 in 63% yield (19% overall yield from isopropylidene glyceraldehyde). The synthesis of the C8-C15 sub-unit 32 was performed in 3.4% overall yield for 13 steps, from the commercially available ester 24, with a Hoppe crotylation as a key step.