Derivatisation of diospyrin, a bisnaphthoquinonoid isolated from Diospyros montana Roxb., led to the modification of its inhibitory activity, in vitro, towards a murine tumour model, Ehrlich ascites carcinoma (EAC), and two human cancer cell lines, viz., malignant skin melanoma (A375) and epidermoid laryngeal carcinoma (Hep2). Among the novel derivatives, an epoxide exhibited the maximum antiproliferative activity (IC50 values in the range of 0.03-0.21 μM) and a comparatively lower toxicity (IC50 ∼ 98 μM) in normal human peripheral blood mononuclear cells (PBMC). This compound might provide a novel 'lead' for the development of clinically effective antiproliferative agents against cancer. © 2007 Elsevier Ltd. All rights reserved.