Limonoids from the fruits of Khaya ivorensis

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.

Biological activities of limonoids in the Genus Khaya (Meliaceae): a review

Background

Limonoids are a class of highly oxygenated modified triterpenoids with a diverse range of biological activities. Although with restricted occurrence in the plant kingdom, these compounds are found extensively in the Meliaceae and Rutaceae families. Limonoids are of great interest in science given that the small number of plant families where they occur exhibit a broad range of medicinal properties that promote health and prevent disease.

Main text

The Meliaceae family includes the genus Khaya and comprises tree species that have been used in traditional medicine to treat several ailments. In recent years, the genus Khaya has attracted much research interest owing to the presence of limonoids in different plant parts of a few species that can serve as therapeutic molecules in the pharmaceutical industry. In this study, a literature search over the past two decades (2000–2020) was conducted on the biological activities of limonoids in the genus Khaya using different databases such as Google Scholar, PubMed, Scopus and ISI Web of Science. The taxonomy, geographical distribution and the various traditional uses of the genus are presented in detail. This study reveals that the currently documented biological activities of limonoids both in vivo and in vitro are limited to four species (K. anthotheca, K. grandifoliola, K. ivorensis and K. senegalensis) in the genus Khaya, and include anticancer, antimalarial, hepatoprotection, anti-inflammatory, neuroprotection, antimicrobial, antifungal and antifeedant. The most well-researched species, K. senegalensis, has the most notable biological activities and traditional uses in the genus Khaya.

Conclusion

The present detailed and up-to-date review of recent literature on the biological activities in the genus Khaya reveals the potentials of limonoids for drug development in managing several ailments.

Genetic diversity in populations of African mahogany (Khaya grandioliola C. DC.) introduced in Brazil

Given its high-valued wood, the African mahogany (Khaya grandifoliola) has been envisaged as a renewable source of tropical hardwoods in Brazil. However, there are concerns about the hypothesized low diversity among the few K. grandifoliola germplasm sources introduced in the country. Using eight microsatellite markers, we evaluated the genetic diversity and divergence among 53 superior trees selected from three provenances of K. grandifoliola located in the state of Para. These populations are among the oldest plantations (>15 years) in Brazil and, therefore, the country's main seed sources. The average number of alleles per locus was 5.9, expected heterozygosity was moderate (^=0.56) and lower than the high observed heterozygosity (H_O=0.74). Therefore, the intrapopulation fixation index was negative (f=-0.31) indicating the possibility that selection of superior trees might have favored heterozygous plants with heterosis. No genetic structure was observed between provenances. The genetic diversity observed within selected trees, with an effective population size (Ne) of 30.4, is comparable to that of natural populations of African and Brazilian mahoganies. Therefore, our results contradict the idea that the genetic diversity of K. grandifoliola introduced in Brazil is low and show that our germplasm can be exploited for breeding purposes.

Triterpenoids

Covering 2014. Previous review: Nat. Prod. Rep., 2017, 34, 90-122 This review covers the isolation and structure determination of triterpenoids reported during 2014 including squalene derivatives, lanostanes, holostanes, cycloartanes, cucurbitanes, dammaranes, euphanes, tirucallanes, tetranortriterpenoids, quassinoids, lupanes, oleananes, friedelanes, ursanes, hopanes, serratanes, isomalabaricanes and saponins; 374 references are cited.

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.

Cytotoxic limonoids from Trichilia americana leaves

Ten cedrelone limonoids were isolated from the leaves of Trichilia americana. These compounds include americanolides A-D (1-4), 1,2-dihydrodeacetylhirtin (5), 1α-hydroxy-1,2-dihydrodeacetylhirtin (6), 1α-hydroxy-1,2-dihydrohirtin (7), 1α-methoxy-1,2-dihydrodeacetylhirtin (8), 11β-hydroxy-12α-propanoyloxycedrelone (9), and 1α,11β-dihydroxy-1,2-dihydrocedrelone (10), as well as two previously reported compounds, deacetylhirtin (11) and hirtin (12). Their structures were characterized on the basis of spectroscopic studies, and the assignment of the absolute configuration of americanolide A (1) was supported by single-crystal X-ray diffraction studies. The cytotoxic activities of all isolated compounds were also evaluated against five human tumour cell lines (HL-60, SMMC-7721, A-549, MCF-7, and SW-480) using an MTS assay. Compounds 11 and 12 showed significant cytotoxicity with IC50 values ranging from 0.1 to 0.5 μM, and compounds 5, 6, 7, 8, 9, and 10 exhibited potent or selective cytotoxic activity with IC50 values ranging from 1.0 to 39.6 μM.