As part of our search for bioactive compounds from the Dichapetalaceae, repeated chromatographic purification of the roots of a hitherto unexamined species, Dichapetalum pallidum, led to the isolation of the newly occurring 7-hydroxydichapetalin P (1) and the known dichapetalins A (2) and X (3). Also isolated were the known compounds friedelin-2,3-lactone (4), friedelan-3-one (6), friedelan-3β-ol (7) and pomolic (8), as well as the dipeptide aurantiamide acetate (5). The compounds were characterized by direct interpretation of their IR, 1D NMR and 2D NMR spectral data and by comparison of their physico-chemical data, including their chromatographic profiles, with the literature and authentic samples in our compound library for the genus Dichapetalum. The compounds were assayed for their anti-proliferative activities against the human T-lymphocytic leukemia (Jurkat), acute promyelocytic leukemia (HL-60) and T-lymphoblast-like leukemia (CEM) cell lines. Overall, dichapetalin X showed the strongest (3.14 μM) and broadest cytotoxic activities against all the leukemic cell lines tested, exhibiting even stronger activities than the standard compound, curcumin.
Keywords: 7-hydroxydichapetalin P; Dichapetalum pallidum; dichapetalin A; dichapetalin X; leukemia; spiroketal.