(−)-Kunstleramide, a New Antioxidant and Cytotoxic Dienamide from the Bark of Beilschmiedia kunstleri Gamble

A new dienamide, (2E,4E)-7-(3',4'-dimethoxyphenyl)-N-ethyl-6-(R)-hydroxyhepta-2,4-dienamide, named (-)-kunstleramide (1), were isolated from the bark of Beilschmiedia kunstleri Gamble together with one neolignan: (+)-kunstlerone (2) and seven known alkaloids: (+)-nornuciferine (3), (-)-isocaryachine (4), (+)-cassythicine (5), (+)-laurotetanine (6), (+)-boldine (7), noratherosperminine (8), (+)-N-demethylphyllocaryptine (9). Their structures were established from spectroscopic techniques, most notably 1D- and 2D-NMR, UV, IR, OR, circular dichroism (CD) spectra and LCMS-IT-TOF. (-)-Kunstleramide (1) exhibited very poor dose-dependent inhibition of DPPH activity, with an IC(50) value of 179.5 ± 4.4 μg/mL, but showed a moderate cytotoxic effect on MTT assays of A375, A549, HT-29, PC-3 and WRL-68 with EC(50) values of 64.65, 44.74, 55.94, 73.87 and 70.95 µg/mL, respectively.