Four limonoids from Bacillus subtilis-fermented neem seeds and their cytotoxic activity.

Four new limonoids, 7,12-dihydroxyvilasinone (1), vilasindione (2), 4-dehydroxynimbandiol (3) and azadiramide B (4), were isolated from extracts of Bacillus subtilis-fermented neem seeds. Their planar structures and relative configurations were elucidated by spectroscopic methods including UV, IR, MS and NMR, and the absolute stereochemistry was determined by comparing their experimental and calculated CD spectra. 4 is a rare salannin-class limonoid alkaloid. In cytotoxic assays, 3 showed inhibitory activity against MDA-MB-231, A375 and Hela cell lines with IC50 values of 21.45 ±â€¯5.41, 17.67 ±â€¯3.96 and 28.13 ±â€¯9.12 µM, respectively, while 4 selectively inhibited growth of MDA-MB-231 cell line with an IC50 value of 15.73 ±â€¯6.07 µM.