Anti-trypanosomal cadinanes synthesized by transannular cyclization of the natural sesquiterpene lactone nobilin

Abstract Acid-catalyzed transannular cyclization of the germacrene-type sesquiterpene lactone nobilin 1 was investigated with the aim of obtaining new anti-trypanosomal cadinane derivatives. The reaction was regiospecific in all tested reaction conditions. Compounds were fully characterized by spectroscopic and computational methods, and the anti-trypanosomal activity was evaluated and compared to nobilin (IC 50 3.19 ± 1.69 μM). The tricyclic derivative 11 showed most potent in vitro activity against Trypanosoma brucei rhodesiense bloodstream forms (IC 50 0.46 ± 0.01 μM). Acid-catalyzed transannular cyclization of natural cyclodecadienes is an efficient strategy to generate new natural product derivatives with anti-protozoal activity.