In this study, we explore the cytotoxic activity of four natural abenquines (2a–d) and fourteen synthetic analogues (2e–j and 3a–h) against a panel of six human cancer cell lines using a SRB assay. It was found that most of the compounds revealed higher levels of cytotoxic activities than naturally occurring abenquines. The analogues carrying ethylpyrrolidinyl and ethylpyrimidinyl with either an acetyl group (2...