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 IC 50 values of 25 and 27 nM, respectively. Pileamartine C ( 1 ), julandine ( 4 ), and cryptopleurine ( 5 ) exhibited cytotoxicity against 4 tested cancer cell lines with IC 50 values less than 1 µM.