A series of C2-arylated analogues of the diketopiperazine brevianamide F has been synthesized using a mild Pd-catalyzed CH-activation procedure. Biological evaluation of the new derivatives in different cell lines shows that this modification is responsible for the remarkable change in activity, turning a mild antibiotic and antifungal natural product (brevianamide F) into novel antitumoral compounds. Furthermore, the approach stated represents a new straightforward and versatile methodology with promising applications in peptidomimetics and medicinal chemistry.