Synthesis and biological activities of new conformationally fixed analogues of (−)-indolactam-V, the core structure of tumor-promoting teleocidins

−)-Indolactam-V (1) exists as two stable conformers, the twist and the sofa form, in solution at room temperature. 3-Aza-Cope rearrangement of (−)-N13-desmethyl-N13-allylindolactam-V (5) gave new conformationally restricted analogues (2a and 3) along with a normal rearrangement product (7). Both 2a and 3, whose fixed conformation was the twist form, showed significant biological activities related to tumor promotion.