Abstract:
Three maleimide-based enediynes with different numbers of hydroxyl groups at the alkyne ends were synthesized by Sonogashira coupling reaction between diiodomaleimide and different terminal alkynes. Through the maleimide assisted rearrangement and cycloaromatization (MARACA) mechanism, these enediyne molecules were converted to enyne-allenes at room temperature, producing highly reactive diradical intermediates through Myer-Saito cyclization reactions. Electron paramagnetic resonance confirmed the generation of free radical intermediates in the system by using the free radical trapping agent, N-tert-Butyl-
α-phenylnitrone. DNA gel electrophoresis indicated that these enediynes generated highly reactive free radicals, which further deprived hydrogen atoms from the DNA backbone at physiological temperature, resulting in the fragmentation of plasmid DNA strands and cleavage of supercoiled DNA into the cyclic form. The DNA cleavage process is concentration-dependent, and different enediyne structures exhibited different cleaving effects over the same concentration gradient. Protein gel electrophoresis showed that the ability of the enediyne compounds to degrade proteins agreed with that to produce free radicals. In the presence of a highly reactive enediyne with an oxygen atom at the propargyl position, the structural integrity of the protein backbone was destroyed at a low concentration (5 mmol/L) of enediyne compounds, resulting in protein denaturing. Taken together, this work provides an insight into exploiting maleimide-based enediyne for the structural degradation of a variety of biological macromolecules such as proteins and oncogenes.