Diterpenoids with Aromatase Inhibitory Activity from the Rhizomes of Kaempferia elegans

Abietane Diterpenoids from the Rhizomes of Kaempferia roscoeana and Their Anti-Inflammatory Activities

Six new abietane diterpenes, roscoeananes A-F (1-6), along with two known compounds (7-8) were isolated from the rhizomes of Kaempferia roscoeana. The structures of all compounds were elucidated by analysis of spectroscopic data, and the absolute configurations were assigned by a comparison of the theoretical and experimental electronic circular dichroism (ECD) spectra and a comparison with literature values. The unreported compound 5 is an ether-linked dimer of roscoeanane B (2). Most of the isolated compounds were tested for their nitric oxide inhibitory effects in lipopolysaccharide-activated RAW264.7 cells. Among them, roscoeanane A (1) was found to reduce NO levels in murine macrophage cells with an IC50 value of 3.58 ± 0.95 μM and exhibited low cytotoxicity (IC50 > 50 μM).

Abietane-Type Diterpenoids: Insights into Structural Diversity and Therapeutic Potential

The abietane-type diterpenoids are among the most significant diterpene subsets found in hundreds of plant species belonging to various families. Among which, the members of the genus Salvia and Euphorbia are rich in abietane diterpenoids. Because of the chemical diversity and notable bioactivities, such as anticancer, antiinflammatory, antimicrobial, and antioxidant activities, they are attractive. Herein, recent advances in the isolation and characterization of abietanes from natural sources, as well as their biological activities, from 2015 up to 2024 are reviewed. During this time, over 300 abietanes with diverse structures have been discovered.

Xanthine Oxidase Inhibition by Monoterpene-Chalcone Conjugates from Kaempferia subglobosa and Molecular Docking Insights

Kaempferia subglobosa is a perennial medicinal plant in the Zingiberaceae family, identified as a new species in January 2024. To uncover the biological benefits of K. subglobosa and its compounds, investigation of the metabolites of the roots and rhizomes, yielded three new monoterpene-chalcone conjugates, the globosones A-C, representing a rare metabolite group within the Zingiberaceae, along with six known compounds. The biogenetic pathway for the globosones involves an oxidative [3+2] cycloaddition between α-phellandrene and 4'-methoxy-4,2',6'-trihydroxychalcone. Biological testing revealed potent xanthine oxidase (XO) inhibition by globosones A and B, with IC50 values of 7.0±1.0 and 3.0±0.2 μM, respectively, surpassing the positive control drug allopurinol (IC50 7.2±0.1 μM). Globosones A-C also showed good aromatase inhibition (IC50 3.0-3.5 μM). Molecular docking studies indicated that globosones A and B may inhibit xanthine oxidase through binding at the FAD domain site. The physicochemical properties of these isolates suggest that they possess characteristics suitable for additional biological assessment in more advanced test systems. This study enhances an understanding of monoterpene-chalcone conjugate inhibitors of XO, and offers preliminary insights into the metabolites and bioactivities of K. subglobosa, uncovering potent biological activities associated with this newly discovered plant species.

Discovery and Bioinspired Synthesis of Salpratone A

Salpratone A (1), a novel abietane diterpenoid containing a unique cis-fused A/B ring, was isolated from Salvia prattii. Bioactivity studies showed that 1 has potent activity in inhibiting platelet aggregation induced by multiple agonists as well as antithrombotic efficacy in the FeCl3-induced rat in vivo thrombosis model. Furthermore, a bioinspired synthesis of 1 from the abundant natural product ferruginol was achieved in 6 steps with a 22% overall yield. The key steps include a stereoselective allyl oxidation and a subsequent regioselective Meinwald rearrangement.

Divergent and Stereoselective Synthesis of Ustusal A, (-)-Albrassitriol, and Elegansin D

The first synthesis of ustusal A as well as expeditious access to (-)-albrassitriol is described as featuring a singlet oxygen [4 + 2] cycloaddition, achieving the desired stereoselectivity for the 1,4-cis-hydroxyl groups. Transformation of (+)-sclareolide to III followed by a key Horner-Wadsworth-Emmons (HWE) reaction and stereospecific allylic oxidation facilitated the first synthesis of elegansin D. The biological evaluation of these natural products together with seven elegansin D analogues was performed, among which several elegansin D analogues exhibited potential anticancer activity against liver cancer HepG2 cells (IC50 = 11.99-25.58 μM) with low cytotoxicity on normal liver HL7702 cells (IC50 > 100 μM).

Kaemtakols A-D, highly oxidized pimarane diterpenoids with potent anti-inflammatory activity from Kaempferia takensis

Four highly oxidized pimarane diterpenoids were isolated from Kaempferia takensis rhizomes. Kaemtakols A-C possess a tetracyclic ring with either a fused tetrahydropyran or tetrahydrofuran motif. Kaemtakol D has an unusual rearranged A/B ring spiro-bridged pimarane framework with a C-10 spirocyclic junction and an adjacent 1-methyltricyclo[3.2.1.02,7]octene ring. Structural characterization was achieved using spectroscopic analysis, DP4 + and ECD calculations, as well as X-ray crystallography, and their putative biosynthetic pathways have been proposed. Kaemtakol B showed significant potency in inhibiting nitric oxide production with an IC50 value of 0.69 μM. Molecular docking provided some perspectives on the action of kaemtakol B on iNOS protein.

11,12-seco-Abietane-type diterpene lactones with potential antiplatelet activity from Salvia prattii

Eleven new abietane-type diterpene lactones, salpratlactones D-N (1-11), including five 11,12-seco-11-nor-abietane diterpenes (1-5), four 11,12-seco-abietane diterpenes (6-9), two 20(10 → 5)-abeo-4,5;11,12-bis-seco-abietane diterpenes (10-11), and two known analogues (12-13), were characterized from Salvia prattii. Notably, compounds 1-3 were characterized by a unique linear 6/6/6 tricyclic skeleton. The structures were established by spectroscopic data interpretation, calculated NMR-DP4+ and electronic circular dichroism analysis, as well as single-crystal X-ray diffraction. A bioactivity study showed that 1, 2, 5, 11, and 12 can potently inhibit platelet aggregation induced by arachidonic acid (AA), with IC50 values of 5.66-16.10 μg/ml, stronger than aspirin. In addition, the lactate dehydrogenase assay showed that they had no effect on platelet integrity. Structurally, the same 1,2-benzopyrone fragments of 1, 2, and 5 should be the important pharmacophore for antiplatelet activity.

The amide derivative of anticopalic acid induces non-apoptotic cell death in triple-negative breast cancer cells by inhibiting FAK activation

Anticopalic acid (ACP), a labdane type diterpenoid obtained from Kaempferia elegans rhizomes, together with 21 semi-synthetic derivatives, were evaluated for their cancer cytotoxic activity. Most derivatives displayed higher cytotoxic activity than the parent compound ACP in a panel of nine cancer cell lines. Among the tested compounds, the amide 4p showed the highest cytotoxic activity toward leukemia cell lines, HL-60 and MOLT-3, with IC50 values of 6.81 ± 1.99 and 3.72 ± 0.26 µM, respectively. More interestingly, the amide derivative 4l exhibited cytotoxic activity with an IC50 of 13.73 ± 0.04 µM against the MDA-MB-231 triple-negative breast cancer cell line, which is the most aggressive type of breast cancer. Mechanistic studies revealed that 4l induced cell death in MDA-MB-231 cells through non-apoptotic regulated cell death. In addition, western blot analysis showed that compound 4l decreased the phosphorylation of FAK protein in a concentration-dependent manner. Molecular docking simulations elucidated that compound 4l could potentially inhibit FAK activation by binding to a pocket of FAK kinase domain. The data suggested that compound 4l could be a potential FAK inhibitor for treating triple-negative breast cancer and worth being further investigated.

Diterpenoids and p-methoxycinnamic acid diol esters from Kaempferia saraburiensis Picheans. (Zingiberaceae): Structural assignment of saraburol and their biological activities

Five undescribed compounds, including three diterpenoids namely, saraburol, saraburanes A and B, and two p-methoxycinnamic acid monoterpene diol esters, named E/Z-saraburinic esters, together with ten known oxygenated isopimarane diterpenoids, were isolated from the whole plant of Kaempferia saraburiensis Picheans. Among these compounds, saraburol possesses an unusual 6/9/6 tricyclic ring system bearing a 1,3-dioxonane-4-one scaffold, which is rarely found in natural products. The structure of isolated compounds was elucidated by spectroscopic methods, including HRESIMS, FTIR, 1D and 2D-NMR, and by comparison with published data, and their absolute configurations were determined by comparison of experimental with calculated ECD spectra and hydrolysis reaction. Using gauge-independent atomic orbital (GIAO) NMR shift calculations coupled with DP4+ probability analyses, biogenetic considerations, and optical rotation allowed for the complete characterization of saraburol. A plausible biosynthetic pathway for saraburol and saraburane A was proposed. The cytotoxicity result indicated that E-saraburinic ester exhibited the most potent activity with an IC₅₀ value of 12.0 μM against MOLT-3 cells with a selectivity index of 12.5. Saraburane B exhibited the most potent activity against Gram-positive bacteria strain Staphylococcus epidermidis with MIC (MBC) value of 25 (50) μg/mL.

Antimicrobial Terpenoids and Polyketides from the Algicolous Fungus Byssochlamys spectabilis RR-dl-2-13

Four new carotane sesquiterpenoids, byssocarotins A-D (1-4), two new nor-sesquiterpenoids, byssofarnesin (5) and byssosesquicarin (6), and three new polyketides, byssoketides A and B (7 and 8) and (8R)-paecilocin A (9a), were obtained from a macroalga-associated strain (RR-dl-2-13) of the fungus Byssochlamys spectabilis. These isolates were identified by a combination of spectroscopic methods, including mass spectroscopy, nuclear magnetic resonance, electronic circular dichroism, and X-ray diffraction. Compounds 1-4 greatly contribute to the diversity of rarely occurring 2,15-epoxycarotane sesquiterpenoids, while 5 and 6 are degradation products of farnesane and sesquicarane precursors, respectively. Compound 7 is a structurally unique furan fatty acid derivative that possesses an aldehyde group and a large conjugated unit, and 8 features a hemiketal group. During antimicrobial assays, 8 showed antagonism against the phytopathogenic fungi Glomerella cingulata, Fusarium oxysporum f. sp. cucumerium, and F. oxysporum f. sp. cubense and the marine-derived bacteria Vibrio parahaemolyticus and V. harveyi with MIC values of 13 to 50 μg/mL.

Sesquiterpene Lactones from Sigesbeckia glabrescens Possessing Potent Anti-inflammatory Activity by Directly Binding to IKKα/β

Chromatographic fractionation of Sigesbeckia glabrescens led to the identification of 10 new sesquiterpene lactones, named siegesbeckialides I-O (1-7) and glabrescones A-C (8-10), along with 14 known analogues. An anti-inflammatory activity assay showed that siegesbeckialide I (1) most potently inhibited LPS-induced NO production in RAW264.7 murine macrophages. Furthermore, siegesbeckialide I suppressed the protein expression of iNOS and COX2, as well as the release of PGE₂, IL-1β, IL-6, and TNF-α in LPS-stimulated RAW264.7 cells. Mechanistically, siegesbeckialide I directly binds to inhibitors of IKKα/β and suppresses their phosphorylation. This leads to the inhibition of IKKα/β-mediated phosphorylation and degradation of inhibitor α of NF-κB (IκBα), as well as the activation of NF-κB signaling.