New amides from the fruits of Piper retrofractum

Three new amides, (2E,14Z)-N-isobutyleicosa-2,14-dienamide (1), dipiperamides F and G (2 and 3), together with 30 known compounds were isolated from the fruits of Piper retrofractum. Their structures were elucidated by extensive spectroscopic analyses including 1D and 2D NMR as well as MS, and by comparison with the literature. A plausible biosynthetic pathway leading to the amides isolated in this study is discussed. All isolated compounds were screened for their antifungal and cytotoxic activities. Piperanine (9) showed growth inhibition against the fungus Cladosporium cladosporioides, while dipiperamides F and G (2 and 3), chabamide (30), nigramide R (31), dehydropipemonaline (24), pipernonaline (25), guineensine (22), brachystamide B (23), retrofractamide C (20), pellitorine (13), and pipericine (14) exhibited considerable cytotoxicity against L5178Y mouse lymphoma cells with IC50 values of 10.0, 13.9, 11.6, 9.3, 8.9, 17.0, 17.0, 16.4, 13.4, 28.3, and 24.2 mu M, respectively. (C) 2015 Elsevier Ltd. All rights reserved.