Semisynthesis, Biological Activity, and Molecular Modeling Studies of C-Ring-Modified Camptothecins

The synthesis, biological activity, and molecular modeling studies of C-ring-modified camptothecins are reported. A general synthetic protocol, based on "C-5 camptothecin (C-5-CPT) enolate chemistry", allows one to obtain various C5-substituted analogues. All new compounds, obtained as 1:1 epimeric mixtures, were tested for their antiproliferative activity. Experimental data showed that all novel derivatives are less active than the reference compounds and that one of the two epimers is more active than the other. Molecular docking simulations were performed to achieve more insight into the interactions between the new C5-modified CPTs and Topo I. A good correlation was observed when the data of cytotoxicity and the values calculated for the free binding energy were combined.