Krishnolides A-D: New 2-Ketokhayanolides from the Krishna Mangrove, Xylocarpus moluccensis

Four new khayanolide-type limonoids with a 2-carbonyl group, named krishnolides A-D (1-4), were isolated from the seeds of an Indian mangrove, Xylocarpus moluccensis, collected in the mangrove swamp of Krishna estuary, Andhra Pradesh. The relative and absolute configurations of these compounds were established by HR-ESIMS, extensive NMR investigations, single-crystal X-ray diffraction analysis with CuKα radiation, and experimental electronic circular dichroism (ECD) spectra. Krishnolides A-D are unusual khayanolides containing two large ester substituents of five or four carbon atoms at the C-3 and C-30 positions, respectively. Krishnolide A, containing an 8,14-epoxy group, exhibited moderate anti-Human Immunodeficiency Virus (HIV) activity with an IC₅₀ value of 17.45 ± 1.65 μM and a CC₅₀ value of 78.45 ± 1.69 μM, respectively. This is not only the first report of natural khayanolides from Indian mangroves of the genus Xylocarpus, but also the first report of the anti-HIV activity of khayanolide.