To access, purchase, authenticate, or subscribe to the full-text of this article, please visit this link: http://dx.doi.org/10.1142/S0192415X14500785 Byline: Nguyen Huu Tung, Mitsuko Suzuki, Takuhiro Uto, Osamu Morinaga, Kofi D. Kwofie, Naa Ammah, Kwadwo A. Koram, Frederic Aboagye, Dominic Edoh, Taizo Yamashita, Yasuchika Yamaguchi, Takao Setsu, Shoji Yamaoka, Nobuo Ohta, Yukihiro Shoyama The crude extract of Alnus japonica bark exhibited a strong effect on the growth of Trypanosoma brucei. Subsequent chromatographic separation resulted in the isolation of two novel diarylheptanoids, known as alnuside C (2) and alnuside D (3), and three known compounds, 1-(3,4-dihydroxyphenyl)-7-(4-hydroxyphenyl)-heptan-3(R)-O-[beta]-D-glucopyranoside (1), oregonin (4) and hirsutanone (5). The structures of the isolates were elucidated based on the use of extensive spectroscopic and chemical methods. Among the isolated diarylheptanoids, oregonin (4) (a major component of plant bark) and hirsutanone (5) exhibited potent in vitro inhibitory activity against T. brucei growth in the bloodstream with IC.sub.50 values of 1.14 and 1.78 [micro]M, respectively. We confirmed that oregonin (4) and hirsutanone (5) were not toxic to human normal skin fibroblast cells (NB1RGB) and colon cancer cells (HCT-15) at a concentration of 50 [micro]M; however, lower levels of toxicity were observed for leukemia cells. To determine the structure activity relationships of the isolated components, we performed Conformation Search and found that the 3-oxo function of the heptane chain in the diarylheptanoid molecule is required for their trypanocidal activity.