Krishnolides E-K: New limonoids from the Krishna mangrove Xylocarpus moluccensis

Divergent Total Syntheses of Phragmalin and Khayanolide-Type Limonoids: A Torquoselective Interrupted Nazarov Approach

The asymmetric and divergent total syntheses of two phragmalin (moluccensins G and H) and two khayanolide-type (krishnolide F and khayseneganin F) limonoids were disclosed, which employed a torquoselective interrupted Nazarov cyclization as the key step. Taken together with a Liebeskind-Srogl coupling, a benzoin condensation, and bidirectional acyloin rearrangements, our strategy would simplify the synthetic design of both phragmalin and khayanolide-type limonoids and facilitate their modular syntheses. Moreover, the described approach also provides additional insights into the biosynthetic relationships between these two distinct skeletons.

Ten limonoids and three protolimonoids from the Thai mangrove Xylocarpus moluccensis

Ten new limonoids, named xylomolones E-N (1-10), and two new protolimonoids, named xylomolones O (11) and P (12), were isolated from seeds of the Thai mangrove Xylocarpus moluccensis, together with the known compound, hispidone acetonide (13). The structures of these compounds were established by extensive NMR spectroscopic data, single-crystal X-ray diffraction analysis, and comparison of experimental ECD spectra. The absolute configurations of xylomolones E (1) and L (8) were unambiguously determined by single-crystal X-ray diffraction analyses, conducted with Cu Kα radiation. Xylomolones E-L (1-8) are mexicanolide-type limonoids, among which xylomolones J (6) and K (7) contain a C7/C28δ-lactone ring, whereas xylomolones M (9) and N (10) are phragmalin-type limonoids. Xylomolones O (11) and P (12) are two new protolimonoids. In addition, the 1H and 13C NMR spectroscopic data for hispidone acetonide (13) was first assigned completely. In bioassay, xylomolones F (2), M (9), and P (12) exhibited moderate inhibitory activity against the production of NO in LPS-induced RAW 264.7 cells with IC50 values of 31.54 ± 7.27, 62.84 ± 17.62, and 22.7 ± 6.56 μM, respectively.

Hainanxylogranolides A-F: New Limonoids isolated from the seeds of Hainan mangrove plant Xylocarpus granatum

Six new limonoids, named hainanxylogranolides A-F (1-6), together with nineteen known ones (7-25) were isolated from the seeds of a Hainan mangrove Xylocarpus granatum. The structures of the new compounds were established by extensive NMR spectroscopic data combined with the DFT and TDDFT calculated electronic circular dichroism spectra. Hainanxylogranolide A (1) is the aromatic B-ring limonoid containing a central pyridine ring and a C-17 substituted γ(21)-hydroxybutenolide moiety. Hainanxylogranolide B (2) belongs to the small group of mexicanolides containing a C₃-O-C₈ bridge, whereas hainanxylogranolides C and D (3 and 4) are mexicanolides comprising a C₁-O-C₈ bridge. Compounds 9 and 25 posed obvious inhibition effect on the tube formation of HUVECs. There are only about 25% tube-like structures were observed at the concentration of 40.0 μM of compound 25. The antiviral activities of the isolates against herpes simplex virus-1 (HSV-1) and severe fever with thrombocytopenia syndrome virus (SFTSV) were tested in vitro. Compound 23 exhibited moderate anti-SFTSV activity with the IC₅₀ value of 29.58 ± 0.73 μM. This is the first report of anti-angiogenic effect and anti-SFTSV activity of limonoids from the genus Xylocarpus.

Unusual Secondary Metabolites from the Mangrove Ecosystems: Structures, Bioactivities, Chemical, and Bio-Syntheses

Mangrove ecosystems are widely distributed in the intertidal zone of tropical and subtropical estuaries or coasts, containing abundant biological communities, for example, mangrove plants and diverse groups of microorganisms, featuring various bioactive secondary metabolites. We surveyed the literature from 2010 to 2022, resulting in a collection of 134 secondary metabolites, and classified them into two major families in terms of the biological sources and 15 subfamilies according to the chemical structures. To highlight the structural diversity and bioactivities of the mangrove ecosystem-associated secondary metabolites, we presented the chemical structures, bioactivities, biosynthesis, and chemical syntheses.

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.