Anti-trypanosomal activity of doubly modified salinomycin derivatives.

As a group of biologically active compounds, polyether antibiotics (ionophores) show a broad spectrum of interesting pharmacological properties, ranging from anti-bacterial to anti-cancer activities. There is increasing evidence that ionophores, including salinomycin (SAL), and their semi-synthetic analogues are promising candidates for the development of drugs against parasitic diseases. Our previous studies have shown that esterification and amidation of the C1 carboxylate moiety of SAL provides compounds with potent activity against Trypanosoma brucei , protozoan parasites responsible for African trypanosomiasis. In this paper, we present the synthetic pathways, crystal structures and anti-trypanosomal activity of C1 esters, amides and hydroxamic acid conjugates of SAL , its C20-oxo and propargylamine analogues as well novel C1/C20 doubly modified derivatives. Evaluation of the trypanocidal and cytotoxic activity using bloodstream forms of T. brucei and human myeloid HL-60 cells revealed that the single-modified C20-oxo and propargylamine precursor molecules 10 and 16 were the most anti-trypanosomal and selective compounds with 50% growth inhibition (GI 50) values of 0.037 and 0.035 μM, and selectivity indices of 252 and 300, respectively. Also the salicylhydroxamic acid conjugate of SAL (compound 9) as well as benzhydroxamic acid and salicylhydroxamic acid conjugates of 10 (compounds 11 and 12) showed promising trypanocidal activities with GI 50 values between 0.032 and 0.035 μM but less favorable selectivities. The findings confirm that modification of SAL can result in derivatives with improved trypanocidal activity that might be interesting lead compounds for further anti-trypanosomal drug development. Image 1 • A library of novel double-modified salinomycin (SAL) analogues was devised. • Compounds 14 and 15 were characterized using the scXRD method. • Two novel analogues, compounds 11 and 12 , showed promising trypanocidal activity. • Most derivatives showed lower cytotoxic activity against HL-60 cells than SAL. • Anti-trypanosomal mechanism of action of newly synthesized compounds was studied. [ABSTRACT FROM AUTHOR]