Limonoids from Swietenia macrophylla and their antitumor activities in A375 human malignant melanoma cells

•Sixteen new and 18 known limonoids from Swietenia macrophylla.•Their structures were determined by by using spectroscopic data and X-ray crystallography.•The cytotoxicities of all the componds were evaluated against four human tumor cell lines (SMMC-7721, SW620, A549, A375).•The inhibitory effects of the new compounds on nitric oxide (NO) production were tested.•Flow cytometric analysis showed that treatment with 19 significantly induced A375 cell apoptosis in a dose-dependent manner.