The synthesis and tumor-inhibitory activity of a series of aminonaphthoquinone derivatives of diospyrin, which was isolated from Diospyros montana Roxb., are presented here for the first time. An aminoacetate derivative showed the maximum (∼93%) increase in life span in vivo against murine Ehrlich ascites carcinoma (EAC) at a dose of 1 mg kg-1 day-1 (ip; five doses), and the lowest IC50 (0.06 μM) in vitro. Further, the same analogue also exhibited considerable enhancement in antiproliferative activity when evaluated against human cell lines, viz. malignant skin melanoma and epidermoid laryngeal carcinoma (IC50 = 0.06 and 0.92 μM, respectively) in comparison to the natural precursor, diospyrin (IC50 = 0.82 and 3.58 μM, respectively). Moreover, diospyrin and all its derivatives were found to show significantly greater (∼17- to 1441-fold) cytotoxicity against the tumor cells as compared to normal human lymphocytes. All these quinonoids generated substantial amounts of reactive oxygen species in EAC cells, more or less commensurate to their respective IC50 values. © 2007 Elsevier Masson SAS. All rights reserved.