“…The guaianolides are one of the largest groups of sesquiterpene lactones isolated from higher plants (Roberts & Bryson, 1984;Fraga, 1985Fraga, , 1986Fraga, , 1987Fraga, , 1988Fraga, , 1990Fraga, , 1992Fraga, , 1993Fraga, , 1994Fraga, , 1995Fraga, , 1996Fraga, , 1997Fraga, , 1998Fraga, , 1999Fraga, , 2000Fraga, , 2001 and they are frequently cited as allelopathic agents, especially in plants of the family Compositae. These sesquiterpene lactones have attracted significant interest due to their biological properties, particularly their antitumor and cytotoxic activities (Bruno et al, 2005;Dirsch et al, 2001;Lee et al, 2001;Rodríguez et al, 1976).…”