Bioactive cholinesterase inhibitions of clerodanes from the flowers of Croton krabas and molecular docking studies.

The first investigation of the phytochemical profile of the flowers of Croton krabas led to the isolation of two new clerodane diterpenes, 6S-crotocaudin (1) and crotocaudin B (2), together with two known clerodanes, 6S-crotoeurin C (3) and isoteucvin (4). The structures and absolute configurations of isolated clerodanes were elucidated by extensive analysis of NMR spectroscopic data, mass spectrometry and ECD calculations. Compounds 1-4 demonstrated significant inhibitory activity towards acetylcholinesterase (AChE). Notably, compound 2 exhibited the strongest AChE inhibition (IC50 1.01 µM). Compounds 3 and 4 showed potent butyrylcholinesterase (BChE) inhibitory activity with IC50 values of 1.09 and 1.12 µM, respectively. The molecular docking results revealed that 2 bound to the catalytic anionic site (CAS) and peripheral anionic site (PAS) of AChE, while 3 occupied in the CAS of BChE.

New norclerodane diterpenoids from bulbils of Dioscorea bulbifera L.

Investigation of extracts from bulbils of Dioscorea bulbifera L. yielded two new norclerodane diterpenoids, diosbulbin N acetate (1) and epi-diosbulbin B (3), together with eleven known compounds. Their structures were established based on spectroscopy. The absolute configurations of 1 and diosbulbin B (2) were determined by X-ray crystallographic analysis using Cu Kα radiation. The absolute configuration of 3 was determined by comparison of its ECD spectrum to that of 2. Isolated phenanthrenes 7, 9 and 10 exhibited moderate cytotoxicity against the HelaS3 cell line with IC50 values of 9.03 ± 0.04, 27.13 ± 6.86 and 10.88 ± 2.75 µM, respectively. In addition, 7-9 and 11 showed potent inhibition of NO production by LPS-induced RAW 264.7 macrophages.

A new feruloylfriedelinol from the stems of Bridelia stipularis and its α-glucosidase inhibition.

Phytochemical investigation of the stems of Bridelia stipularis led to the isolation of a new triterpene, 3ß-O-trans-feruloylfriedelinol (1), together with five known compounds, friedelin (2), 3ß-friedelinol (3), lupeol (4), stigmasterol (5), and 4-(1,5-dimethyl-3-oxo-4-hexenyl)benzoic acid (6). Their structures were identified by intensive spectroscopic analysis including 1D and 2D nuclear magnetic resonance, infrared, and mass spectrometry. Compound 1 showed significant α-glucosidase inhibitory activity (IC50 = 337.49 ± 0.59 µM) close to the standard, acarbose. Furthermore, the structure activity relationship of 1 was analyzed by molecular docking studies. In addition, the molecular docking results showed that the interaction between 1 and the active site occurred through hydrophobic forces and hydrogen bonds.

Isopimarane-type diterpenoids from the rhizomes of Kaempferia galanga L. and their biological activities.

Fourteen isopimarane diterpenoids (1-14) were isolated from the rhizomes of Kaempferia galanga, including four new compounds (1-4). The isolated secondary metabolites were identified through analysis of spectroscopic (1 D and 2 D NMR) and mass spectrometric data, together with X-ray diffraction studies. Compounds 4-5, 7-11, and 13 showed strong antimalarial activities, with IC50 values in the range of 1.46-3.99 µg/mL. Moreover, compounds 4, 5, 8, and 12 showed cytotoxicity against KB cell line with IC50 values in the range of 6.13-38.2 µg/mL, while compounds 4, 5, and 12 showed cytotoxicity against MCF-7 cell line with IC50 values in the range of 11.75-47.4 µg/mL. Eventually, the isolated compounds were screened against six bacterial strains and Mycobacterium tuberculosis, demonstrating weak to moderate activities.

Neolignans and polyoxygenated seco-cyclohexenes from the stems and leaves of Piper suipigua Buch.-Ham. ex D. Don.

Five new compounds including, a neolignan, eupomatenoid-19 (1) and four polyoxygenated seco-cyclohexenes, artahongkongenes G-J (2-5), together with fifteen known compounds (6-20) were isolated from the stems and leaves of Piper suipigua Buch.-Ham. ex D. Don. Their structures were determined by spectroscopic evidence (IR, UV, 1H NMR, 13C NMR and 2 D NMR) as well as MS. The absolute configurations of polyoxygenated seco-cyclohexenes 2-8 were identified by NOESY data and by comparison of their experimental and calculated ECD spectral data. Neolignans, eupomatenoid-19 (1) and eupomatenoid-7 (10), displayed cytotoxicity against several cancer cell lines. In addition, eupomatenoid-7 (10) showed antibacterial activity against Bacillus cereus, Bacillus subtilis and Staphylococcus aureus.

Discovery of lead natural products for developing pan-SARS-CoV-2 therapeutics.

The COVID-19 pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), remains a global public health crisis. The reduced efficacy of therapeutic monoclonal antibodies against emerging SARS-CoV-2 variants of concern (VOCs), such as omicron BA.5 subvariants, has underlined the need to explore a novel spectrum of antivirals that are effective against existing and evolving SARS-CoV-2 VOCs. To address the need for novel therapeutic options, we applied cell-based high-content screening to a library of natural products (NPs) obtained from plants, fungi, bacteria, and marine sponges, which represent a considerable diversity of chemical scaffolds. The antiviral effect of 373 NPs was evaluated using the mNeonGreen (mNG) reporter SARS-CoV-2 virus in a lung epithelial cell line (Calu-3). The screening identified 26 NPs with half-maximal effective concentrations (EC50) below 50 µM against mNG-SARS-CoV-2; 16 of these had EC50 values below 10 µM and three NPs (holyrine A, alotaketal C, and bafilomycin D) had EC50 values in the nanomolar range. We demonstrated the pan-SARS-CoV-2 activity of these three lead antivirals against SARS-CoV-2 highly transmissible Omicron subvariants (BA.5, BA.2 and BA.1) and highly pathogenic Delta VOCs in human Calu-3 lung cells. Notably, holyrine A, alotaketal C, and bafilomycin D, are potent nanomolar inhibitors of SARS-CoV-2 Omicron subvariants BA.5 and BA.2. The pan-SARS-CoV-2 activity of alotaketal C [protein kinase C (PKC) activator] and bafilomycin D (V-ATPase inhibitor) suggest that these two NPs are acting as host-directed antivirals (HDAs). Future research should explore whether PKC regulation impacts human susceptibility to and the severity of SARS-CoV-2 infection, and it should confirm the important role of human V-ATPase in the VOC lifecycle. Interestingly, we observed a synergistic action of bafilomycin D and N-0385 (a highly potent inhibitor of human TMPRSS2 protease) against Omicron subvariant BA.2 in human Calu-3 lung cells, which suggests that these two highly potent HDAs are targeting two different mechanisms of SARS-CoV-2 entry. Overall, our study provides insight into the potential of NPs with highly diverse chemical structures as valuable inspirational starting points for developing pan-SARS-CoV-2 therapeutics and for unravelling potential host factors and pathways regulating SARS-CoV-2 VOC infection including emerging omicron BA.5 subvariants.

Cytotoxic and antibacterial xanthones from the roots of Maclura cochinchinensis.

Three new furanoxanthones, macochinxanthones A-C (1-3) and sixteen known xanthones (4-19) were isolated from the roots of Maclura cochinchinensis. Their structures were elucidated by spectroscopic analysis including NMR, UV and IR, as well as mass spectrometry. Chiral-phase HPLC analysis of 1-3 revealed that they were scalemic mixtures with an enantiomeric excess (ee) of 0.05%, 36.8% and 8%, respectively. Most of the isolated xanthones exhibited potent cytotoxicity against four cancer cell lines (KB, HelaS3, A549 and HepG2) with IC50 values in the range of 1.29-90.15 µM. In addition, many of them displayed antibacterial activity against Gram-positive bacteria and Methicillin resistant Stephylococus aureus (MRSA) with MIC values in the range of 4-128 µg/mL.

Four New Anthraquinones with Histone Deacetylase Inhibitory Activity from Ventilago denticulata Roots.

Chromatographic separation of the crude extracts from the roots of Ventilago denticulata led to the isolation of four new anthraquinones, ventilanones L-O (1-4), together with eight known anthraquinones (5-12). Their structures were elucidated by spectroscopic methods (UV, IR, 1H NMR, 13C NMR, and 2D NMR) and mass spectrometry (MS), as well as comparison of their spectroscopic data with those reported in the literature. HDACs inhibitory activity evaluation resulted that compound 2 exhibited moderate antiproliferative activity against HeLa and A549 cell lines but nontoxic to normal cell. Molecular docking indicated the phenolic functionality of 2 plays crucial interactions with class II HDAC4 enzyme.

Chitosan biological molecule improves bactericidal competence of ceftazidime against Burkholderia pseudomallei biofilms.

Biofilm-associated Burkholderia pseudomallei infections (melioidosis) are problematic because of reduced sensitivity to antibiotics and high frequency of relapse. Biofilm dispersal agents are essential to liberate the biofilm-encased cells, which then become planktonic and are more susceptible to antibiotics. This study aimed to evaluate the ability of deacetylated chitosan (dCS), an antimicrobial and antibiofilm biological macromolecule, to disrupt established biofilms, thus enabling ceftazidime (CAZ) to kill biofilm-embedded B. pseudomallei. We combined dCS with CAZ using a mechanical stirring method to generate dCS/CAZ. In combination, 1.25-2.5 mg ml-1 dCS/1-2 µg ml-1 CAZ acted synergistically to kill cells more effectively than did either dCS or CAZ alone. Notably, a combination of 5-10 mg ml-1 dCS with 256-512 µg ml-1 CAZ, prepared either by mechanical stirring (dCS/CAZ) or mixing (dCS + CAZ), drastically improved bactericidal activities against biofilm cells leading to a 3-6 log CFU reduction. Confocal laser-scanning microscope (CLSM) images revealed that 10 mg ml-1 dCS/512 µg ml-1 CAZ is by far the best formulation to diminish B. pseudomallei biofilm biomass and produces the lowest live/dead cell ratios of B. pseudomallei in biofilm matrix. Collectively, these findings emphasize the potential of novel therapeutic antibacterial and antibiofilm agents to fight against antibiotic-tolerant B. pseudomallei biofilm-associated infections.

Three new indole diterpenoids from Aspergillus aculeatus KKU-CT2.

Three new indole diterpenoids, aculeatupenes A-C (1-3), together with four known compounds (4-7), were isolated from the mycelium of Aspergillus aculeatus KKU-CT2. Their structures were established by spectroscopic evidence and absolute configurations of 1-3 were determined by comparison of their experimental and calculated ECD spectra. Compounds 1, 2, and emindole SB (4) showed weak cytotoxicity against HelaS3, KB, HepG2, MCF-7, and A549 cancer cell lines with IC50 values in the range of 11.12-67.81 µM. Compound 3 showed weak cytotoxicity against HelaS3 cell lines with an IC50 value of 17.48 µM but non-cytotoxicity against Vero cell line. In addition, compound 1 exhibited weak antibacterial activity against Bacillus cereus.[Formula: see text].

Cytotoxic and α-glucosidase inhibitory metabolites from twigs and leaves of Phyllanthus mirabilis, a species endemic to limestone mountains.

The first investigation of Phyllanthus mirabilis Müll.Arg. led to the isolation of six undescribed compounds including two tyramine derivatives: phyllatyramines A and B; three butenolide analogues, phyllantenolide, phyllantenocoside-O-gallate and epi-phyllantenocoside-O-gallate; and a flavanonol gallate, (-)-taxifolin-3-O-gallate; as well as two first isolated natural products, phyllatyramine C and phyllantenocoside; together with twenty-three known compounds. Their structures were elucidated by spectroscopic means. ECD spectra of all isolated butenolides were compared and assigned the configurations. Phyllatyramine A displayed weak cytotoxicity against the KB cell line, while phyllatyramines B and C showed weak cytotoxicity against KB and HeLa cell lines. In addition, phyllatyramine B and (-)-taxifolin-3-O-gallate showed more potent α-glucosidase inhibitory activity than the standard acarbose 3.4 and 5.8 fold, respectively.

Chemical constituents and antibacterial activity from the stems and leaves of Piper wallichii.

A phytochemical investigation of the stems and leaves of Piper wallichii led to the isolation of two new compounds, an aryl alkanone, piwalkanone (1) and a dioxoaporphine alkaloid, piwallidione (2), together with nine known compounds, a dioxoaporphine alkaloid, cepharadione A (3); two aristolactams, piperolactam A (4) and stigmalactam (5); a piperidine, piperine (6); four isobutylamides, piperlonguminine (7), pellitorine (8), N-isobutyl-2E,4E-octadecadienamide (9), and guineensine (10); and a tyramine, N-trans-feruloyltyramine (11). Their structures were elucidated on the basis of spectroscopic evidence (IR, 1H NMR, 13C NMR and 2 D NMR) and MS. Compounds 2 and 3 showed inhibitory activities against pathogenic bacteria, Bacillus cereus, Bacillus subtilis and Staphylococcus aureus.

Cytotoxic and antibacterial depsidones from the endophytic fungus Chaetomium brasiliense isolated from Thai rice.

Four new depsidones, mollicellins V-Y (1-4), together with eight known depsidones (5-12) were isolated from the endophytic fungus, Chaetomium brasiliense, detached from stems of Thai rice. Their structures were determined by extensive spectroscopic methods. Mollicellins X, H, and F (3, 8 and 10) showed potent cytotoxicity against the human oral epidermoid carcinoma (KB) cell line, and mollicellin F (10) also showed a potent cytotoxicity against the human hepatocellular carcinoma (HepG2) cell line. Besides, mollicellin B (11) exhibited cytotoxicity against the colorectal adenocarcinoma (HT-29) cell line. Moreover, most of the isolated depsidones displayed potent antibacterial activity against Gram-positive bacteria, Bacillus cereus and Bacillus subtilis, and several of them showed moderate activity against Methicillin-resistant Staphylococcus aureus (MRSA) and clinical isolates of S. aureus. In addition, a few of them also showed moderate activity against a Gram-negative bacteria Pseudomonas aeruginosa.

A New Apotirucallane from Walsura trichostemon Leaves and Its Antibacterial and α-Glucosidase Inhibitory Activities.

Phytochemical investigation of Walsura trichostemon leaves led to the isolation of a new apotirucallane-type triterpenoid, 11,25-dideacetyl-16-hydroxytrichostemonate (1), along with two known apotirucallane-type triterpenoids (2 and 3), two known tirucallane-type triterpenes (4 and 5), and two known steroids (6 and 7). Their structures were identified by intensive analysis of 1D and 2D nuclear magnetic resonance, infrared, and mass spectrometry data, which were compared with data reported in the literature. Compounds 2, 3, and 5 exhibited moderate antibacterial activity against Pseudomonas aeruginosa (minimum inhibitory concentration (MIC) value: 64 µg/mL), and compound 4 showed weak antibacterial activity against P. aeruginosa (MIC: 128 µg/mL). Furthermore, compound 5 displayed activity against Bacillus cereus (MIC: 64 µg/mL). In addition, compound 4 showed stronger α-glucosidase inhibitory activity than the control, acarbose. The active compound 4 was subjected to molecular docking experiments using AutoDock4 and revealed precise interactions with the active gorge of the enzyme through hydrogen bonding, supporting the in vitro results.

ent-Clerodane diterpenoids from the stems of Croton krabas.

The first phytochemical investigation from the stems of Croton krabas resulted in the isolation of three new ent-clerodane diterpenoids, crotonkrabases A-C (1-3), along with two known compounds, 12-oxohardwickiic acid (4) and crotonpyrone B (5). Their structures were elucidated using extensive spectroscopic methods. The structure of 3 was unambiguously proven by X-ray crystallography. Furthermore, the absolute configurations of compounds 1-3 were identified by NOESY and the comparison of their experimental ECD spectra with those of calculated ECD spectra reported in the literature. Compounds 1, 2, and 5 showed antibacterial activities against two Gram-positive bacteria (Bacillus cereus and Bacillus subtilis); whereas compound 4 exhibited weak antibacterial against B. cereus. In addition, compound 4 showed potent α-glucosidase inhibitory activity, which was lower than the reference standard acarbose.

New Pyrrolobenzoxazine Sesquiterpenoid Derivatives from the Fungus Talaromyces trachyspermus.

Three new pyrrolobenzoxazine sesquiterpenoids, talatrachyoxazines A - C (1:  - 3: ), together with fourteen known compounds (4:  - 17: ), were isolated from the fungus Talaromyces trachyspermus EU23. Their structures were identified by spectroscopic evidence and mass spectrometry. The absolute configurations of 1:  - 3: were determined by NOESY data and comparison of their calculated and experimental electronic circular dichroism (ECD) spectra. Compound 1: showed cytotoxic activity against HelaS3, KB, HT-29, MCF-7, and HepG2 cell lines with IC50 values of 7, 11, 10, 12, and 10 µM, respectively. Compounds 1: and 14: showed weak antibacterial activity against the gram-positive bacteria Bacillus cereus and Bacillus subtilis, while 1:  - 3: and 14: showed weak antibacterial activity against the gram-negative bacterium Pseudomonas aeruginosa. In addition, compound 1: showed weak antibacterial activity against Escherichia coli.

Bioactive secondary metabolites from roots of Cissus rheifolia planch.

Two new aromadendrin rhamnosides, cissusfoliate A (1) and 3-epi-cissusfoliate A (2) together with seven known compounds (3-9) were isolated from the roots of Cissus rheifolia Planch. Their structures were determined by extensive spectroscopic methods. The absolute configurations of compounds 1-5 were assigned by combination of the J coupling constant values of H-2 and H-3 and the comparison of their experimental ECD spectra with those reported in literature. Compounds 1, 3 and 5-8 showed antioxidant effects on ORAC, ATBS and DPPH assays as well as antibacterial activity against six pathogenic bacterial strains. Their cytotoxicity against Hela, KB, MCF-7, HepG2 and HT-29 cell lines were also evaluated.

Inhibition of nitric oxide production by clerodane diterpenoids from leaves and stems of Croton poomae Esser.

Chromatographic separation of crude extracts from the leaves and stems of Croton poomae Esser led to the isolation of two new clerodane diterpenes crotonolide K (1) and furocrotinsulolide A acetate (2) and six known clerodane diterpenes (3-8), together with twelve known compounds (9-20). Their structures were established from spectroscopic analysis. The clerodane diterpenoids 1-8 were evaluated for inhibition of nitric oxide (NO) production in LPS-activated RAW 264.7 macrophages. Compounds 1, 2, 5, 7 and 8 showed potent inhibitory effects, with IC50 values ranging from 32.19 to 48.85 µM, which is better than both the standard drugs indomethacin (154.5 µM) and dexamethasone (56.28 µM).

A new antibacterial tirucallane from Walsura trichostemon roots.

Phytochemical investigation of the roots of Walsura trichostemon, a Thai medicinal plant, provided a new tirucallane, 3-epimesendanin S 12-acetate (1), together with four known compounds, 3-epimesendanin S (2), meliasenin G (3), ß-sitosterol (4) and ß-sitosterol glucoside (5). Their structures were characterized by intensive spectroscopy including 1 D and 2 D NMR, UV, IR and MS spectrometric analysis. The isolated compounds were evaluated for antibacterial and acetylcholinesterase inhibitory activities. Compounds 1-2 showed antibacterial activity against Bacillus cereus and Bacillus subtilis with MIC values ranging from 16-128 µg/mL. In addition, compound 3 was active against Pseudomonas aeruginosa and Escherichia coli with MIC values of 64 and 128 µg/mL, respectively.