Four new chemical constituents from Piper pleiocarpum.

Two new polyoxygenated cyclohexenes (1–2), one new benzoate derivative (3), and one new dineolignan (4) together with one known neolignan (5) were isolated from whole plants of Piper pleiocarpum. The structures of these compounds were determined by extensive spectroscopic methods including 1D, 2D NMR, HR-ESI-MS, and by comparison with the literature. The 13C NMR spectra of the known compound 5 were completely assigned for the first time. All isolated compounds (1–5) were evaluated for their cytotoxic activities against five human cancer cell lines (including A-549, SMMC-7721, HL-60, MCF-7, and SW-480), Only compound 4 showed inhibitory activity against MCF-7 cell line with IC50 value of 18.24 ± 0.69 μM.