Bioassay-Guided Isolation and Identification of Cytotoxic Compounds from Melaleuca quinquenervia Fruits.

The fruit extract of Melaleuca quinquenervia yielded a total of 19 compounds, including two novel spiro-biflavonoid enantiomers (1a and 1b) and a chalcone derivative (3). Their structures were determined through spectroscopic analysis. The enantiomers of the racemic mixture of compound 1 were successfully resolved into (+)-1 and (-)-1 using chiral-phase HPLC. Single-crystal X-ray diffraction analysis was also used to confirm the structure of 1. The enantiomeric configurations of 1 and 2 were determined through a comparison of the calculated and experimental electronic circular dichroism spectra. Compounds 2 (melanervin), 14 (methyl betulinate), 15 (3-O-acetylbetulinic acid), and 16 (pyracrenic acid) were found to be highly cytotoxic, with compound 16 showing superior growth inhibition of nonsmall cell lung cancer cells (A549 cells) (IC50 2.8 ± 0.1 µM) compared to cisplatin (IC50 3.3 ± 0.0 µM), a positive control chemotherapeutic drug. Both compound 16 and cisplatin were significantly more cytotoxic toward A549 lung cancer cells compared to nontumorigenic Vero E6 cells.

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.

Bioactive xanthones, benzophenones and biphenyls from mangosteen root with potential anti-migration against hepatocellular carcinoma cells.

Liver cancer refers primarily to hepatocellular carcinoma (HCC) accounting for over 90% of cases and is the highest incidence in men in Thailand. Over the past decades, the incidence of HCC dramatically increased with a strong rise of mortality rates. Garcinia mangostana, "Queen of Fruit" of Thailand, is known as a rich source of xanthones with potent cytotoxic properties against various cancer cells. Study on xanthones is provoking not only due to the structural diversity but also a wide variety of pharmacological activities. Hence the aim of the current study is to determine the effects of metabolites from G. mangostana root on cell proliferation and migration of hepatocellular carcinoma cells. Twenty-two metabolites, including two new benzophenones and one new biphenyl, were isolated and characterized. Five xanthones with a prenyl moiety showed significant cytotoxicity against both HCC cells tested; however, only dulxanthone D displayed the most promising activity on the migration of Huh7 HCC cells, comparable to sorafenib, a standard drug. Moreover, the compound dose-dependently induced apoptosis in Huh7 cells via mitochondrial pathway. Accordingly, dulxanthone D held a great potential for development as a novel migration inhibitor for effective HCC treatment.

Cassane-type diterpenes from roots of Pterolobium macropterum and their anti-inflammatory activity.

Eight undescribed cassane diterpenes, pterolobirins C-J, together with two known analogs, were isolated from the roots of Pterolobium macropterum. Their structures were characterized by extensive spectroscopic techniques including NMR, MS, ECD and X-ray crystallographic spectroscopy. The absolute configuration of pterolobirin J was confirmed by single-crystal X-ray diffraction data. The compounds were screened for their anti-inflammatory activity on the lipopolysaccharide (LPS) induced nitric oxide (NO) production in J774. A1 macrophage cells. Pterolobirin E and sucutinirane C displayed good NO inhibition with IC50 values of 24.44 ± 1.34 and 19.16 ± 1.22 µM, respectively.

Picrotoxane sesquiterpene and α-pyrone derivative from Dendrobium signatum and their free radical scavenging potency.

One new picrotoxane sesquiterpene (1) and one new α-pyrone derivative (4), together with nine known compounds, were isolated from the aerial parts of Dendrobium signatum. The structures of the new compounds were elucidated based on the interpretation of 1D and 2D NMR, HRESIMS and electronic circular dichroism (ECD) data. The absolute configuration of 1 was confirmed by single-crystal X-ray diffraction data. The new α-pyrone 4 exhibited promising ABTS scavenging activity with IC50 value of 0.7 µM.

Cytotoxicity and Nitric Oxide Production Inhibitory Activities of Compounds Isolated from the Plant Pathogenic Fungus Curvularia sp.

Chemical investigation of the mycelia of the pathogenic fungus Curvularia sp. which was isolated from a leaf of Dactyloctenium aegyptium (crowfoot grass), resulted in the isolation of a new compound, curvulariahawadride (5), along with five known compounds (1-4, and 6). Their structures were determined on the basis of spectroscopic data, including 1D and 2D NMR and HRESIMS. The absolute configuration of 5 was established from experimental and calculated electronic circular dichroism (ECD). Compounds 1, 3, and 5 showed nitric oxide (NO) production inhibitory activity with IC50 values of 53.7, 32.8, and 12.8 µM, respectively. Compounds 2 and 4 showed significant cytotoxicity against lung cancer A549, colorectal cancer SW480, and leukemic K562 cells with an IC50 ranging value of 11.73 to 17.59 µM.

Two new xanthones from the root of Thai Calophyllum inophyllum and their toxicity against colon and liver cancer cells.

Two new xanthones, 1,3,6,7-tetrahydroxy-5-methoxy-4-(1',1'-dimethyl-2'-propenyl)-8-(3″,3″-dimethyl-2″-propenyl)-xanthone (1) and (2'S)-7-hydroxy caloxanthone B (2), were isolated from the root of Thai Calophyllum inophyllum Linn., together with twelve known xanthones (3-14). The structures of new compounds were elucidated based on spectroscopic data. In addition, compounds 4, 6 and 8 were isolated from the genus Calophyllum for the first time. The isolated compounds were evaluated for their cytotoxic activity against colon HCT-116 and liver Hep-G2 cancer cells. Among tested compounds, xanthones 5 and 14 possessing a prenyl moiety and a pyranyl ring fused at C-2 and C-3 displayed the most potent and selective cytotoxicity against HCT-116 colon cancers with the same IC50 values of 3.04 µM.

Pterolobirins A and B, Oxygen-Bridged Cassane Diterpenoid Dimers from the Fruits of Pterolobium macropterum.

Two dimeric cassane diterpenoids with an unprecedented 6/6/6/6/6/5/6/6/6 nonacyclic framework, pterolobirins A and B (1 and 2), were isolated from the fruits of Pterolobium macropterum. Their structures were assigned by interpreting the spectroscopic data. The absolute configuration of 1 was unequivocally confirmed by single-crystal X-ray diffraction data. A putative biosynthetic pathway is proposed based on a regular intermolecular Diels-Alder reaction and an intramolecular nucleophilic addition.

Bioassay-guided isolation and identification of antidiabetic compounds from Garcinia cowa leaf extract.

Garcinia cowa Roxb. ex Choisy (Clusiaceae) is a Thai local edible plant, which has been used for the treatment of diabetes. The aim of this study is to discover and identify bioactive compounds related to antidiabetic properties from the leaf extract of G. cowa. α-Glucosidase inhibitory bioassay-guided isolation of the ethyl acetate extract of the leaves of G.cowa resulted in the isolation and identification of 11 compounds. Of these, a decahydro-1H-xanthene derivative, garciniacowone K (1), was identified as a novel compound. Their structures were characterized by spectroscopic data and by comparison of their NMR spectroscopic data with those previously reported. All compounds were evaluated for their α-glucosidase inhibitory and glucose consumption activities. Compound 2 showed the highest efficacy in inhibiting α-glucosidase enzyme and promoting glucose consumption activity by 3T3-L1 cells, with IC50 values of 0.5 µM and 13.1 µM, respectively, without causing toxicity to cells.

Phloroglucinol Benzophenones and Xanthones from the Leaves of Garcinia cowa and Their Nitric Oxide Production and α-Glucosidase Inhibitory Activities.

Five new compounds-two phloroglucinol benzophenones, garciniacowones F (1) and G (2), and three xanthones, garciniacowones H (3), I (4), and J (5)-together with seven known xanthones (6-12) were isolated from the fresh leaves of Garcinia cowa. Their structures were elucidated by detailed analysis of NMR and MS data. Compounds 1 and 2 are phloroglucinol benzophenones containing a polyprenylated bicyclo[3.3.1]nonane ring system, while compounds 3-5 are rare xanthones having farnesyl (3 and 5) and geranylgeranyl (5) units at C-8. Compounds 1, 3, 4, 7, 8, and 10 exhibited inhibitory effects on NO production in LPS-induced RAW264.7 macrophage cells with IC50 values ranging from 5.4 to 18.6 µM. Compounds 4 and 8 had α-glucosidase inhibitory activities with IC50 values of 15.4 and 11.4 µM, respectively, which were more potent than that of the acarbose control.

Antibacterial and Inhibitory Activities against Nitric Oxide Production of Coumaronochromones and Prenylated Isoflavones from Millettia extensa.

A chemical investigation of leaf and root extracts of Millettia extensa led to the isolation and structural elucidation of four new prenylated isoflavones, millexatins G-J (1-4), and three new coumaronochromones, millexatins K-M (5-7), along with 16 known compounds. The structures of the new compounds were determined on the basis of NMR and MS data. Compound 4 is a rare isoflavone having a 2-hydroxyethyl moiety at C-8, whereas the structures of compounds 5-7 formally arise from a ring closure through HO-2' and C-2. The absolute configurations at the C-2 and C-3 positions of 5 and 6 were determined from their ECD spectra through comparison with those of previously reported compounds. Most of compounds were evaluated for their inhibitory effects against nitric oxide (NO) production on RAW264.7 macrophages and their antibacterial activities. Compounds 18 and 19 inhibited NO production with IC50 values of 8.5 and 14.3 µM, respectively. Compounds 13 and 14 showed antibacterial activity against various Gram-positive bacteria with MIC values ranging from 2 to 8 µg/mL.

A tocotrienol quinone dimer and xanthones from the leaf extract of Garcinia nigrolineata.

Four new compounds (1-4) together with six known compounds (5-10) were isolated from the leaf extract of Garcinia nigrolineata. Compound 4 is a rare tocotrienol quinone dimer. The structures were elucidated based on NMR and MS data. All isolated compounds were evaluated for their antibacterial activities.

Antibacterial Prenylated Isoflavonoids from the Stems of Millettia extensa.

The first phytochemical investigation of the stem extract of Millettia extensa resulted in the isolation and identification of six new isoflavones, millexatins A-F (1-6), together with 16 known compounds. The structures of these new compounds were determined on the basis of their spectroscopic data. Millexatin A (1) is a rare isoflavone containing three isoprenyl units on a modified A ring. Compounds 1, 6, 10, 11, and 14 displayed promising antibacterial activity with MIC values of 2-8 µg/mL.

New Benzophenones and Xanthones from Cratoxylum sumatranum ssp. neriifolium and Their Antibacterial and Antioxidant Activities.

Two new benzophenones (1 and 2) and four new xanthones (4-6 and 17) together with 24 known compounds (3, 7-16, and 18-30) were isolated from the roots and twigs of Cratoxylum sumatranum ssp. neriifolium. Their structures were elucidated by spectroscopic methods. Compounds 5 and 26 showed antibacterial activity against Micrococcus luteus, Bacillus cereus, and Staphylococcus epidermis with minimum inhibitory concentrations ranging from 4 to 8 µg/mL, whereas compounds 7, 20, and 26 displayed selective antibacterial activities against Staphylococcus aureus (8 µg/mL), Salmonella typhimurium (4 µg/mL), and Pseudomonas aeruginosa (4 µg/mL), respectively. The radical scavenging effects of some isolated compounds were investigated. Compounds 11 and 21 exhibited potent activity against 2,2-diphenyl-1-picrylhydrazyl (DPPH) with IC50 values of 7.0 ± 1.0 and 6.0 ± 0.2 µM, respectively.

Bioactive Xanthones from Cratoxylum cochinchinense.

Chemical investigation of Cratoxylum cochinchinense stem bark has led to the isolation and identification of a new xanthone, cochinchinone M (1), together with 12 known compounds. Their structures were elucidated on the basis of spectroscopic methods, including UV, IR, NMR and MS. Some compounds were evaluated for their antibacterial and acetylcholinesterase inhibitory activities.

Monoterpene indole alkaloids from the twigs of Kopsia arborea.

The phytochemistry of Kopsia arborea Blume has received considerable attention, which has resulted in the isolation of a number of new unusual indole alkaloids with intriguing structures. In this study, a new eburnane-type alkaloid, phutdonginin (1), together with eight known alkaloids: 19-OH-(-)- eburnamonine (2), melodinine E (3), kopsinine (4), kopsilongine (5), kopsamine (6), (-)-methylenedioxy-1 1,12-kopsinaline (7), decarbomethoxykopsiline (8), and vincadifformine (9), were isolated from the twigs of K. arborea. Their structures were characterized extensively by 1D and 2D NMR spectroscopy and HR-ESI-MS. All compounds were submitted to TLC screening for acetylcholinesterase inhibitory activities. Only kopsamine and decarbomethoxykopsiline showed AChE inhibition with MIR values of 12.5 and 6.25 µg, respectively, compared with galanthamine (positive control, 0.004 µg). In addition, compounds 1 and 2 inhibited moderate antibacterial activity against E. coli TISTR 780 with the MIC value of 32 .g/mL.

Antibacterial compounds from the roots of Cratoxylumformosum spp. pruniflorum.

Phytochemical investigation of the roots of Cratoxylum formosum spp. pruniflolnnm led to the isolation and identification of a new xanthone, namely cratopruniforone (1), together with 13 known compounds (2-14). Some of these more abundant compounds were evaluated for their antibacterial activities.