Antiprotozoal and cytotoxic naphthalene derivatives from Diospyros assimilis

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 H-1 and C-13 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 IC50 values of 19.82, 12.28 and 38.78 mu M and displayed cytotoxicity towards rat skeletal myoblasts (L-6 cells) with IC50 of 174.94 mu M, 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 IC50 of 1.12 and 8.82 mu M and 12.94 and 16.66 mu M respectively. (c) 2006 Elsevier Ltd. All rights reserved.