Diterpenoids and Limonoids from the Leaves and Twigs of Swietenia mahagoni

Research progress of meliaceous limonoids from 2011 to 2021

Covering: July 2010 to December 2021Limonoids, a kind of natural tetranortriterpenoids with diverse skeletons and valuable insecticidal and medicinal bioactivities, are the characteristic metabolites of most plants of the Meliaceae family. The chemistry and bioactivities of meliaceous limonoids are a continuing hot area of natural products research; to date, about 2700 meliaceous limonoids have been identified. In particular, more than 1600, including thirty kinds of novel rearranged skeletons, have been isolated and identified in the past decade due to their wide distribution and abundant content in Meliaceae plants and active biosynthetic pathways. In addition to the discovery of new structures, many positive medicinal bioactivities of meliaceous limonoids have been investigated, and extensive achievements regarding the chemical and biological synthesis have been made. This review summarizes the recent research progress in the discovery of new structures, medicinal and agricultural bioactivities, and chem/biosynthesis of limonoids from the plants of the Meliaceae family during the past decade, with an emphasis on the discovery of limonoids with novel skeletons, the medicinal bioactivities and mechanisms, and chemical synthesis. The structures, origins, and bioactivities of other new limonoids were provided as ESI. Studies published from July 2010 to December 2021 are reviewed, and 482 references are cited.

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.

Recent progress in the chemistry and biology of limonoids

Significant limonoids: new isolated limonoids, and recent developments in the total chemical synthesis, and structural modifications of limonoids regarding the bioactivities have been summarised.

Lactam Triterpenoids from the Bark of Toona sinensis

Three new limonoid-type triterpenoids, namely toonasins A-C (1-3) with a rare lactam E ring, along with six known compounds (4-9) were isolated from the barks of Toona sinensis. The structures of new compounds were elucidated by interpretation of spectroscopic data, and the relative configuration of compound 1 was further characterized by X-ray crystallographic analyses. The isolated compounds were evaluated for their cytotoxic activities against five human tumor cell lines (HL-60, SMMC-7721, A-549, MCF-7 and SW480), and compounds 3 and 5 showed weak cytotoxicities.

Antiviral Limonoids Including Khayanolides from the Trang Mangrove Plant Xylocarpus moluccensis

Eight new khayanolides, named thaixylomolins G-N (1-8), two new phragmalins (9 and 10), and two new mexicanolides (11 and 12) were obtained from the seeds of the Trang mangrove plant Xylocarpus moluccensis. The absolute configurations of these limonoids, except for the stereocenter at C-6 of 11 and 12, were assigned by experimental and TDDFT calculated electronic circular dichroism spectra. The khayanolides may be classified into two subclasses, one of which has a C-2 carbonyl and a 3β-acetoxy group, whereas the other possesses a 2β-acetoxy and a C-3 carbonyl function. Khayanolides, rearranged phragmalin-type limonoids, are reported for the first time from plants of the mangrove genus Xylocarpus. The structure of moluccensin J, a known 30-ketophragmalin containing a Δ(8(14)) double bond, was revised to be a khayanolide, named thaixylomolin K. The antiviral activities of the isolates against pandemic influenza A virus (subtype H1N1) were tested by the assay of cytopathic effect inhibition. Three khayanolides, viz., thaixylomolins I, K, and M, exhibited moderate anti-H1N1 activities. The most potent one, thaixylomolin I (IC50 = 77.1 ± 8.7 μM), showed stronger inhibitory activity than that of the positive control, ribavirin (IC50 = 185.9 ± 16.8 μM).

Mexicanolide limonoids with in vitro neuroprotective activities from seeds of Khaya senegalensis

Fourteen new mexicanolide-type limonoids khasenegasins A–N (1–14) were isolated from the seeds of Khaya senegalensis, and bioactivity scan indicated that these mexicanolide-type limonoids displayed neuroprotective activities.