Efficient relay syntheses and assessment of the DNA-cleaving properties of the pyrrole alkaloid derivatives permethyl storniamide A, lycogalic acid A dimethyl ester, and the halitulin core

Abstract

Palladium catalyzed Suzuki- and Negishi cross coupling reactions are used to convert the now readily available 3,4-dibromopyrrole derivatives 13 and 26 into the core structures of different pyrrole alkaloids. Several compounds of this series exhibit respectable cytotoxicity and resensitize multidrug resistant (MDR) cancer cell lines at non-toxic concentrations. Cytotoxicity and MDR reversal can be efficiently uncoupled by per- O-methylation of the peripheral hydroxyl groups. For the storniamide core structure 9 it is demonstrated that this chemical modification goes hand in hand with a complete loss of the DNA-cleaving capacity of the alkaloid.