Total syntheses of thiocoraline and BE-22179 and assessment of their DNA binding and biological properties

Full derails of the total: syntheses of thiocoraline (1) and BE-22179 (2), C-2 symmetric bicyclic octadepsipeptides: possessing two pendant 3-hydroxyquinoline chromophores, are described in which their relative and absolute stereochemistry were established. Key elements:of the approach include the late-stage introduction of the chromophore, symmetrical; tetrapeptide coupling, macrocyclization of, the 26-membered octadepsipeptide conducted at the single secondary amide site following disulfide formation, and a convergent assemblage:of the tetradepsipeptide with introduction of The labile thiol ester linkage in the final coupling reaction under-near racemization free conditions. By virtue of the late-stage introduction of the chromophore and despite the challenges this imposes on the synthesis, this approach provides ready access to a range of key chromophore analogues. Thiocoraline and BE-22179 were shown to bind to DNA by high-affinity bisintercalation analogous to echinomycin, but with little or no perceptible sequence selectivity. Both 1 and 2 were found to exhibit exceptional cytotoxic activity (IC50 = 200 and 400 pM, respectively, L1210 cell line) comparable to echinomycin and one analogue, which bears the luzopeptin chromophore, was also found to be a potent cytotoxic agent.