Novel benzo[d]imidazole-2(3H)-thiones as potent inhibitors of the alpha-melanocyte stimulating hormone induced melanogenesis in melanoma B16 cells.

In order to determine the optimum size of heterocycle of lead compound 1 (6-methyl-3-phenethyl-3,4-dihydro-1H-quinoline-2-thione; IC(50)=0.8 microM) for inhibition of melanogenesis, we have synthesized and evaluated some benzimdazole-2(3H)-thiones 5a-e. The preliminary bioassay has shown that the benzimdazole-2(3H)-thione motif of 5 is essential structural unit for their inhibitory activity. Among all thiones 5a-e, the compound 5d strongly inhibited the formation of melanin with IC(50) value of 1.3 microM.