Cytotoxic Alkaloids from Leaves of Pilea aff. martinii.

Two new phenanthroquinolizidine alkaloids (1 and 2) and a new piperidine derivative (3) were isolated from the leaves of Pilea aff. martinii together with 3 known alkaloids: julandine (4), cryptopleurine (5), and 1,3,6,6-tetramethyl-5,6,7,8-tetrahydro-isoquinolin-8-one (6). Their structures were determined by spectral data analyses including mass spectrometry and 2-dimensional nuclear magnetic resonance data. The absolute configurations of 1-3 were established by comparison of their experimental circular dichroism data with the calculated electronic circular dichroism spectra. The isolated compounds were evaluated for their cytotoxicity against 4 cancer cell lines: KB (mouth epidermal carcinoma cells), HepG-2 (human liver hepatocellular carcinoma cells), LU-1 (human lung adenocarcinoma cells), and MCF-7 (human breast cancer cells). The new phenanthroquinolizidine pileamartine D (2) showed strong and selective proliferation inhibition toward KB and HepG-2 cells with IC50 values of 25 and 27 nM, respectively. Pileamartine C (1), julandine (4), and cryptopleurine (5) exhibited cytotoxicity against 4 tested cancer cell lines with IC50 values less than 1 mu M.