Twenty-Nine New Limonoids with Skeletal Diversity from the Mangrove Plant, Xylocarpus moluccensis.

Twenty-nine new limonoids-named xylomolins A₁-A₇, B₁-B₂, C₁-C₂, D-F, G₁-G₅, H-I, J₁-J₂, K₁-K₂, L₁-L₂, and M-N, were isolated from the seeds of the mangrove plant, . Compounds - are mexicanolides with one double bond or two conjugated double bonds, while belongs to a small group of mexicanolides with an oxygen bridge between C1 and C8. Compounds - are khayanolides containing a Δ double bond, whereas and are rare khayanolides containing a Δ double bond and Δ, Δ conjugated double bonds, respectively. Compounds and are unusual limonoids possessing a ()-bicyclo[5.2.1]dec-3-en-8-one motif, while and are 30-ketophragmalins with Δ, Δ conjugated double bonds. Compounds and are phragmalin 8,9,30- esters, whereas and are azadirone and andirobin derivatives, respectively. The structures of these compounds, including absolute configurations of -, -, and , were established by HRESIMS, extensive 1D and 2D NMR investigations, and the comparison of experimental electronic circular dichroism (ECD) spectra. The absolute configuration of was unequivocally established by single-crystal X-ray diffraction analysis, obtained with Cu Kα radiation. The diverse cyclization patterns of - reveal the strong flexibility of skeletal plasticity in the limonoid biosynthesis of . Compound exhibited weak antitumor activity against human triple-negative breast MD-MBA-231 cancer cells with an IC value of 37.7 μM. Anti-HIV activities of , , , , , , , -, and were tested in vitro. However, no compounds showed potent inhibitory activity.