Synthetic studies on concanamycin A: Synthesis of the C5∼C13 and C20∼C28 segments

Concanamycin H from the soil actinomycete Streptomyces sp. R1706-8

The actinomycete strain R1706-8 is isolated from a soil sample collected from the nest of the horned-face bee ( Osmia cornifrons) and identified as Streptomyces sp. based upon the results of 16SrRNA sequence analysis. Two concanamycin derivatives obtained from the solid fermentation have been determined by analysis of the infrared, high-resolution electrospray ionization mass spectrometry, 1D and 2D NMR spectra as well as by comparison with literature data. Of the two derivatives, one is a new compound, named concanamycin H, and the other is the known compound, concanamycin G. These compounds are assayed for antibacterial activity, with concanamycins H and G displaying inhibitory activity against Bacillus subtilis (minimum inhibitory concentration = 0.625 µg mL−1).

Vacuolar-type H(+)-ATPase inhibitory activity of synthetic analogues of the concanamycins: is the hydrogen bond network involving the lactone carbonyl, the hemiacetal hydroxy group, and the C-19 hydroxy group essential for the biological activity of the concanamycins?

Synthetic analogue of the concanamycins, which lacks the hydrogen bond network existing in the concanamycin structure, retains vacuolar-type H(+)-ATPase (V-ATPase) inhibitory activity and induces apoptosis to cancer cells that overexpressing epidermal growth factor receptors (EGFR).

Total synthesis of bafilomycin A(1) relying on iterative 1,2-induction in acyclic precursors

The macrolide bafilomycin A(1) was synthesized starting from D-valine and D-mannitol as chiral progenitors of propionate units. Acyclic subunits corresponding to different parts of the molecule were constructed based on an iterative 1,2-asymmetric induction protocol as a distinctive feature of the synthesis. The assembly of two segments encompassing the entire carbon framework of the macrolide was achieved by using a Stille coupling. The resulting seco-ester was further manipulated to provide crystalline bafilomycin A(1) via a conventional carbodiimide-mediated Keck-type macrolactonization.

The first total synthesis of concanamycin f (concanolide a)

A highly stereoselective total synthesis of the macrolide antibiotic concanamycin F (1), a specific and potent inhibitor of vacuolar H(+)-ATPase, has been achieved by a convergent route involving the synthesis and coupling of its 18-membered tetraenic lactone and beta-hydroxyl hemiacetal side chain subunits. The C1-C19 18-membered lactone aldehyde 4 was synthesized through the intermolecular Stille coupling of the C5-C13 vinyl iodide 24 and the C14-C19 vinyl stannane 25, followed by construction of the C1-C4 diene and macrolactonization. Synthesis of 4 via a second convergent route including the esterification of the C1-C13 vinyl iodide 45 and the C14-C19 vinyl stannane 47 followed by the intramolecular Stille coupling was also realized. The highly stereoselective aldol coupling of 4 and the C20-C28 ethyl ketone 5 followed by desilylation provided 1 which was identical with natural concanamycin F.