Abstract
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.
Highlights
Plants of the genus Xylocarpus, belonging to the family Meliaceae, are mangroves mainly found in East Africa, India, Bangladesh, Southeast Asia, Southern China, and Northern Australia
Thaixylomolin I, a khayanolide-type limonoid obtained from the Thai X. moluccensis, exhibited stronger inhibitory activity against pandemic influenza A virus than that of the antiviral drug, ribavirin [6]
In order to search for new antiviral limonoids, seeds of the Indian X. moluccensis, collected in the mangrove swamp of Krishna estuary, Andhra Pradesh, were further investigated to afford four new khayanolides, named krishnolides A–D (1–4) (Figure 1)
Summary
Plants of the genus Xylocarpus, belonging to the family Meliaceae, are mangroves mainly found in East Africa, India, Bangladesh, Southeast Asia, Southern China, and Northern Australia. A variety of limonoids with abundant structural diversity and various bioactivities, such as antiviral and antitumor activities, were identified from seeds of the mangrove X. moluccensis [4,5,6,7]. Thaixylomolin I, a khayanolide-type limonoid obtained from the Thai X. moluccensis, exhibited stronger inhibitory activity against pandemic influenza A virus (subtype H1N1) than that of the antiviral drug, ribavirin [6]. In order to search for new antiviral limonoids, seeds of the Indian X. moluccensis, collected in the mangrove swamp of Krishna estuary, Andhra Pradesh, were further investigated to afford four new khayanolides, named krishnolides A–D (1–4) (Figure 1). We report the isolation, structural elucidation, and anti-HIV activities of these khayanolides.
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