Synthesis and evaluation of isatins and thiosemicarbazone derivatives against cruzain, falcipain-2 and rhodesain

While commercial isatins were practically inactive against the target proteases, thiosemicarbazone derivatives were found to be active. The most active compound from the series displayed an inhibitory IC50 value of 1 μM against rhodesain. One thiosemicarbazone was found to be active against all three proteases with inhibitory IC50 values of 10 μM or less. A combination of N-benzylation and appropriate substitution on the aromatic portion of the isatin scaffold was generally found to be beneficial especially against cruzain for ketone inhibitors.