Trichiconins A–C, Limonoids with New Carbon Skeletons from Trichilia connaroides

Cycloartane-type triterpenoids and steroids from Trichilia connaroides and their multidrug resistance reversal activities

Four undescribed cycloartane-type triterpenoids (1-4) and seven undescribed steroids (6-12), along with five known analogues (5 and 13-16), were isolated from the leaves of Trichilia connaroides. Their structures were identified based on the NMR data and HRESIMS, and the absolute configurations were determined through single-crystal X-ray diffraction analysis, Mosher's method, and ECD calculations. The multidrug resistance (MDR) reversal activities of all the isolates were assessed, and compounds 10 and 11 showed significant activities to reverse the MDR of MCF-7/DOX cells with IC50 values of 2.90 and 3.76 μM, respectively. These bioactive compounds may bring fresh insights into the research and development of MDR reversal agents.

Secotrijugins A-D, four highly oxidized and rearranged limonoids from Trichilia sinensis and their anti-inflammatory activity

Four undescribed highly oxidized and rearranged limonoids, secotrijugins A-D, were purified from the leaves and twigs of Trichilia sinensis. Within them, secotrijugin A was characterized as a rare 30-nortrijugin-type limonoid with an unusual cleavage of 1,14-ether bond, secotrijugins B and C represented new examples with the cleavage of δ-lactone ring D, and secotrijugin D was a rare trijugin-type limonoid with an unusual 2,6-oxygen bridge. The structures of limonoids were characterized by means of spectroscopic analysis and ECD calculations. The cellular screening revealed that secotrijugin B was the most active against LPS-stimulated NO production in BV-2 cells, which played an anti-inflammatory role by downregulating COX-2 and iNOS protein expression. The further in vivo experiments confirmed that secotrijugin B had strong in vivo anti-inflammatory effect via suppressing NO and ROS generation.

Ursane and 24-Noroleanane-Type Triterpenoids with Anti-HIV Activity from the Twigs and Leaves of Antirhea chinensis

Investigations on the twigs and leaves of Antirhea chinensis have led to the discovery of two undescribed pentacyclic triterpenoids ( 1 and 2 ) and nine known analogues. Compounds 1 and 2 , each assigned as the ursane and 24-noroleanane-type triterpenoids, featuring similar oxidation pattern of 3 β ,6 β ,19 α -trihydroxy-28-carboxyl. Their structures were elucidated via comprehensive analyses of spectroscopic data. Compound 1 displayed potent anti-HIV activity (EC 50 = 1.24 μ M) and high selectivity index (SI > 32.3).

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.

Structurally diverse limonoids and bio-active evaluation from Trichilia connaroides

Four new limonoids, named as trichiconlide G (1), 2-hydroxyltrijugin F (2), 23-oxo-21-hydroxyltrijugin F (3), 21-oxo-23-hydroxyltrijugin F (4), along with sixteen known analogues (5-20) were isolated from the leaves and twigs of Trichilia connaroides. Their structures and absolute configurations were determined by spectroscopic analyses, X-ray diffraction analysis, and TD-DFT-ECD calculations. Trichiconlide G (1) is one rare naturally occurring 1,2-seco phragmalin-type limonoid bearing a C-7/28 δ-lactone ring. Additionally, 2-hydroxyltrijugin F (2), 23-oxo-21-hydroxyltrijugin F (3), and 21-oxo-23-hydroxyltrijugin F (4) are three naturally occurring limonoids with a rare C-16/8 δ-lactone ring. All isolates were evaluated for their cytotoxic and anti-inflammatory activities. None of compounds exhibited cytotoxicity against five human cancer cell lines A-549, HepG2, 5-8F, Siha, and SCC-4 at the concentration of 40 μM. Compounds 16 and 17 showed moderate anti-inflammatory activity with IC₅₀ values of 28.45 ± 2.51 and 22.66 ± 2.01 μM, respectively.

Natural product sciences: an integrative approach to the innovations of plant natural products

The study on plant natural products not only helps us understand that their structural diversity is the inevitable result of plant species diversity, but also helps us understand certain rules and unity of the inevitable connection between the two. The diversity and complexity of chemical structures of many natural products are beyond imagination before we elucidated their structures. The question that follows is what is the biological significance of these natural products. Intrigued by the relationship between plant resources, natural products and biological functions, the Hao laboratory has taken an integrative approach that employs tools and knowledge from multi-disciplines, including natural product chemistry, chemical ecology and chemical biology, to unveil the effects of plant natural products on plant resistance to diseases, and environmental acclimations. Collaborating with cell biologists, the research has resulted in discovery of new mechanisms of cellular signaling and lead compounds.

Recent advances in natural anti-HIV triterpenoids and analogs

The human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) epidemic is one of the world's most serious health challenges. Although combination antiretroviral therapy provides effective viral suppression, current medicines used against HIV cannot completely eradicate the infectious disease and often have associated toxicities and severe side effects in addition to causing drug resistance. Therefore, the continued development of new antiviral agents with diverse structures and novel mechanisms of action remains a vital need for the management of HIV/AIDS. Natural products are an important source of drug discovery, and certain triterpenes and their analogs have demonstrated potential as pharmaceutical precursors for the treatment of HIV. Over the past decade, natural triterpenoids and analogs have been extensively studied to find new anti-HIV drugs. This review discusses the anti-HIV triterpenoids and analogs reported during the period of 2009-2019. The article includes not only a comprehensive review of the recent anti-HIV agent development from the perspective of medicinal chemistry, but also discusses structure-activity relationship analyses of the described triterpenoids.

Ciliatasecones A–C, three rearranged limonoids from Toona ciliata var. yunnanensis

Three rearranged limonoids with a novel ring-seco model and an unprecedented cycle system were isolated from Toona ciliata var. yunnanensis.

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.

Trijugin- and mexicanolide-type limonoids from the fruits of Heynea trijuga that reverse multidrug resistance in MCF-7/DOX cells

Eleven previously undescribed limonoids, trichisins A-K, including eight structural analogues A-H of trijugin and three H-J mexicanolide derivatives, together with two known mexicanolide derivatives were isolated from the fruits of Heynea trijuga Roxb. ex Sims. The structure determination was based on extensive physical data analyses (NMR, MS), and their basic skeletons and the absolute configurations of trichisins A, B, E, K and trichiconnarone A were assigned via X-ray crystallographic analysis (Cu Kα radiation). The hemiketal motifs in trijugins A, B, and E-G are rare in limonoids. Bioactivity screenings suggested that the trijugin H and mexicanolide-type trichiconnarones A and B limonoids were effective in reversing resistance in MCF-7/DOX cells at a nontoxic concentration of 50 μM with IC₅₀ values of 12.45, 10.86, and 14.96 μM, respectively.

Trichiconlides CF, four new limonoids with 1,2-seco phragmalin-type carbon skeleton from the fruits of Trichilia connaroides

Phytochemical investigation of the fruits from Trichilia connaroides led to the isolation of four rare 1,2-seco phragmalin-type limonoids (1-4) with C-7/28 δ-lactone ring along with two known triterpenoids (5-6). An oxygen bridge between C-1 and C-2 formed an rare 9-oxa-tricyclo[3.3.2.1^7,10]undecane-2-ene moiety in structure of 1 and 2, and 3-4 possessed a bicyclo[5.2.1^4,10]decane skeleton. Their structures were established based on extensive spectroscopic methods and their absolute configurations of 1 were confirmed by TDDFT/ECD calculation and comparative analysis. Compounds 5-6 showed moderate inhibitory effects on Hela tumor cell lines with inhibition ratio values of 83.8% and 87.1% at concentration 40μM, respectively.

Guianolactones A and B, Two Rearranged Pentacyclic Limonoids from the Seeds of Carapa guianensis

Two novel rearranged limonoids, guianolactones A (1) and B (2), were isolated from Carapa guianensis Aubl. (Meliaceae) seeds. The structures of 1 and 2 with their absolute configurations were elucidated in detailed examinations using single-crystal X-ray diffraction analyses and 2D NMR spectra. Guianolactone A (1) has a novel 5/6/6/6/6 pentacyclic core including two δ-lactone and a tetrahydropyran ring, while guianolactone B (2) is a novel limonoid with a 6/6/5/6/6 pentacyclic core featuring a δ-lactone and a tetrahydrofuran ring.

Limonoids from the roots of Trichilia sinensis and their cytotoxicities

Six new compounds (1-4, 8, 10), along with six known limonoids (5-7, 9, 11, 12), were isolated from the roots of Trichilia sinensis. Their structures were elucidated on the basis of extensive spectroscopic methods including ¹H NMR, ¹³C NMR, DEPT, HSQC, HMBC, ¹H-¹H COSY and ROESY experiments, as well as by comparison with the literature. All the compounds were evaluated for cytotoxicities against K562, SGC-7901 and BEL-7402 cell lines. Compounds 2, 7, 10, 11, and 12 showed weak inhibitory activity to the selected cell lines.

Gelsekoumidines A and B: Two Pairs of Atropisomeric Bisindole Alkaloids from the Roots of Gelsemium elegans

Two pairs of atropisomeric bisindole alkaloids, gelsekoumidines A (1) and B (2), with a new carbon skeleton, were isolated from the roots of Gelsemium elegans. Compounds 1 and 2 represent the first examples of seco-koumine-gelsedine type alkaloids, which feature an unprecedented 20,21-seco-koumine scaffold fused with a gelsedine framework via a double bond. Their structures including absolute stereochemistry were elucidated by spectroscopic data, single-crystal X-ray diffraction, and electronic circular dichroism (ECD) calculation. A plausible biogenetic pathway for the new compounds is also proposed. Compound 2 exhibited a moderate inhibitory effect against nitric oxide (NO) production.

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.

Phragmalin-type limonoids from the roots of Trichilia sinensis

Twelve new limonoids were isolated from Trichilia sinensis. Some compounds exhibited cytotoxicity and acetylcholinesterase-inhibiting activity.

Spirotrichilins A and B: Two Rearranged Spirocyclic Limonoids from Trichilia connaroides

Spirotrichilins A (1) and B (2), two novel limonoids with an unprecedented spiro[cyclopenta[b]furan-2,1'-cyclopentan] ring system in A/B/C rings, were isolated from the fruits of trichilia connaroides. Their planar structures and absolute configurations were established based on 1D-, 2D-NMR data, electronic circular dichroism (ECD) exciton chirality method and time-dependent density functional theory (TDDFT)/ECD calculation. A benzilic acid-like rearrangement in ring A was proposed as the key step in the plausible biogenetic pathway of 1 and 2.

Cipacinoids A-D, Four Limonoids with Spirocyclic Skeletons from Cipadessa cinerascens

Four limonoids, cipacinoids A-D (1-4), with spirocyclic skeletons were isolated from Cipadessa cinerascens. It is particularly notable that compounds 1-3 had a 17S-configuration for the first time in the limonoid family. Their structures with absolute configurations were assigned by spectroscopic data, X-ray crystallography, and CD analysis. Compound 1 showed moderate protein tyrosine phosphatase 1B (PTP1B) inhibition.

Trichiconlides A and B: two novel limonoids from the fruits of Trichilia connaroides

Trichiconlides A (1) and B (2), two novel limonoids, were isolated from the fruits of Trichilia connaroides. Compound 1 is a novel limonoid with a highly rearranged A/B ring system and an intact D ring, which formed an unprecedented 5/6/5/6/5 carbon skeleton. Trichiconlide B (2) possesses a 10-oxatricyclo[3.3.1.(3,8)]decane core and formed a cage-like structure located between rings A and C. Their structures and absolute configurations were elucidated by spectroscopic methods, single crystal X-ray diffraction, the ECD exciton chirality method and TDDFT/ECD calculations. 1 showed a moderate inhibitory effect on nitric oxide (NO) production.

Limonoids with Anti-HIV Activity from Cipadessa cinerascens

Sixteen new limonoids, named ciparasins A-P (1-16), comprising three structural categories of trijugin-type (1-7), cipadesin-type (8-15), and prieurianin-type (16) compounds, as well as 15 known limonoid analogues (17-31), were isolated from Cipadessa cinerascens. Ciparasins E-G (5-7) were found to possess a rare γ-hydroxylbutenolide moiety at C-17. Ciparasins B (2) and P (16) showed significant anti-HIV activities, with EC50 values of 5.5 ± 0.6 (SI >7.2) and 6.1 ± 0.7 (SI >6.5) μM, respectively.