Antiprotozoal and cytotoxic naphthalene derivatives from Diospyros assimilis

Abstract Chemical investigation of the roots of Diospyros assimilis had led to the isolation and characterization of six naphthalene derivatives, two 2-naphthaldehyes, namely 4-hydroxy-3,5-dimethoxy-2-naphthaldehyde 1 , 4-hydroxy-5-methoxy-2-naphthaldehye 2 , its related isomer 5-hydroxy-4-methoxy-2-naphthaldehyde 3 and three commonly occurring naphthoquinones, diospyrin 4 , 8′-hydroxyisodiospyrin 5 and the simple monomer, plumbagin 6 . Their chemical structures were established by detailed NMR investigations including 1 H and 13 C NMR, HSQC, HMBC and NOESY experiments. In addition, the naphthalene derivatives 1–5 were evaluated for their in vitro antiprotozoal activity against protozoan parasites belonging to the genera Trypanosoma , Leishmania and Plasmodium . Among the tested compounds, naphthaldehyde 1 showed moderate inhibition of the growth of the parasites, T. brucei , T. cruzi , L. donovani with IC 50 values of 19.82, 12.28 and 38.78 μM and displayed cytotoxicity towards rat skeletal myoblasts (L-6 cells) with IC 50 of 174.94 μM, while 2 and 3 were found to be comparatively less active to 1 . The dimeric quinones 4 and 5 exhibited good activity against T. brucei and L. donovani with IC 50 of 1.12 and 8.82 μM and 12.94 and 16.66 μM respectively.