Plant extracts obtained from the U.S. National Cancer Institute's Open Repository collection have been screened for their ability to inhibit the G 2 DNA damage checkpoint. An extract of Duguetia odorata showed promising activity in the assay. Bioassay-guided fractionation revealed that oliveroline (1) was responsible for the G2 checkpoint inhibitory activity of the D. odorata extract. The new alkaloid JV-methylguatterine (2) was identified during this investigation. © 2007 American Chemical Society and American Society of Pharmacognosy.