Computational Methods Reveal a Series of Cyclic and Linear Lichenysins and Surfactins from the Vietnamese Marine Sediment-Derived Streptomyces Strain G222.

The Streptomyces strain G222, isolated from a Vietnamese marine sediment, was confidently identified by 16S rRNA gene sequencing. Its AcOEt crude extract was successfully analyzed using non-targeted LC-MS/MS analysis, and molecular networking, leading to a putative annotation of its chemical diversity thanks to spectral libraries from GNPS and in silico metabolite structure prediction obtained from SIRIUS combined with the bioinformatics tool conCISE (Consensus Annotation Propagation of in silico Elucidations). This dereplication strategy allowed the identification of an interesting cluster of a series of putative cyclic and linear lipopeptides of the lichenysin and surfactin families. Lichenysins (3-7) were isolated from the sub-fraction, which showed significant anti-biofilm activity against Pseudomonas aeruginosa MUC-N1. Their structures were confirmed by detailed 1D and 2D NMR spectroscopy (COSY, HSQC, HMBC, TOCSY, ROESY) recorded in CD3OH, and their absolute configurations were determined using the modified Marfey's method. The isolated lichenysins showed anti-biofilm activity at a minimum concentration of 100 µM. When evaluated for antibacterial activity against a panel of Gram-positive and Gram-negative strains, two isolated lichenysins exhibited selective activity against the MRSA strain without affecting its growth curve and without membranotropic activity. This study highlights the power of the MS/MS spectral similarity strategy using computational methods to obtain a cross-validation of the annotated molecules from the complex metabolic profile of a marine sediment-derived Streptomyces extract. This work provides the first report from a Streptomyces strain of combined cyclic and linear lichenysins and surfactins, known to be characteristic compounds of the genus Bacillus.

Five undescribed aryltetralin lignans with cytotoxic activities from the fruits of Cleistanthus eberhardtii.

Five undescribed lignans, cleiseberharnins A-D (1-4), cleiseberharside A (5) were isolated from the fruits of Cleistanthus eberhartii (Phyllanthaceae), together with six known aryltetralin lignans, cleistantoxin (6), picroburseranin (7), neocleistantoxin (8), 7-hydroxypicropolygamain (9), cleisindoside D (10), and cleisindoside A (11). Their structures and relative configurations were established by analysis of HRESIMS and NMR data, and quantum chemical calculations of JH,H coupling constants. The absolute configurations of 1-5 were determined by analysis of their experimental CD spectra and comparison with calculated electronic circular dichroism (ECD) spectra. All compounds (1-11) were evaluated for their cytotoxicity against KB, MCF-7, HepG-2, and Lu-1 human cancer cell lines. Among the tested compounds, compounds 6 and 7 showed strong activity against KB, MCF7, HepG2 and Lu-1 cell lines with IC50 values in the range of 0.02-0.62 µM. Compound 1 showed activity against three cancer cell lines KB, HepG2, and Lu-1 with IC50 values of 6.98, 7.61 and 11.75 µM, respectively. Compound 2 exhibited a selective inhibition with moderate cytotoxicity against Lu-1 with IC50 value of 15.30 µM. Compounds 4, 5 and 9 showed moderate activity against the three cancer cell lines with IC50 values in the range of 8.73-19.70 µM.

Two new flavonoids with antimicrobial activity from the roots of Byttneria aspera Colebr. ex Wall (Malvaceae).

Two new flavonoids, 4',5,7-trihydroxy-5'-methoxy-6,8-dimethylisoflavone (1) and 2',5',7-trihydroxy-5-methoxy-6,8-dimethylflavanone (2) together with the known flavonoids 4´,5,7-trihydroxy-3´-methoxy-6.8-dimethylflavone (3), epigallocatechin (4), 4´-O-methylepicatechin (5) and quercetin (6) were isolated from the roots of Byttneria aspera. The structures of these compounds were determined by means of spectroscopic methods. Compounds 1-6 were submitted to cytotoxic activity assays against three cancer cell lines including KB, MCF7 and A549, as well as their antimicrobial activity against a panel of clinically significant microorganisms. Compound 6 showed moderate cytotoxic activity with IC50 values of 12.7, 56.9 and 17.5 µM against KB, MCF7 and A549. Interestingly, the new compounds 1 and 2 exhibits antimicrobial activity, with compound 1 displaying selective antifungal activity against Candida albicans giving an MIC value of 128 µg/mL, compared to cyclohexamide with 32 µg/mL, while compound 2 shows potent inhibition of the Gram-positive bacterium Enterococcus faecalis displaying an MIC of 64 µg/mL, compared to streptomycin with 256 µg/mL.

New Phenolic Lipids from the Leaves of Clausena harmandiana Inhibit SARS-CoV-2 Entry into Host Cells.

Induced by the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the COVID-19 pandemic underlined the clear need for antivirals against coronaviruses. In an effort to identify new inhibitors of SARS-CoV-2, a screening of 824 extracts prepared from various parts of 400 plant species belonging to the Rutaceae and Annonaceae families was conducted using a cell-based HCoV-229E inhibition assay. Due to its significant activity, the ethyl acetate extract of the leaves of Clausena harmandiana was selected for further chemical and biological investigations. Mass spectrometry-guided fractionation afforded three undescribed phenolic lipids (1-3), whose structures were determined via spectroscopic analysis. The absolute configurations of 1 and 2 were determined by analyzing Mosher ester derivatives. The antiviral activity against SARS-CoV-2 was subsequently shown, with IC50 values of 0.20 and 0.05 µM for 2 and 3, respectively. The mechanism of action was further assessed, showing that both 2 and 3 are inhibitors of coronavirus entry by acting directly on the viral particle. Phenolic lipids from Clausena harmandiana might be a source of new antiviral agents against human coronaviruses.

Rare flavonoids and sesquiterpenoids isolated from the leaves of Goniothalamus gracilipes.

Three previously undescribed benzopyranyl sesquiterpenes gracilipins BD (1-3) and two flavonoids 5,4'-dihydroxy-6-(2-hydroxybenzyl)-3,7,3'-trimethoxyflavone (4), and 5,4'-dihydroxy-8-(2-hydroxybenzyl)-3,7-dimethoxyflavone (5) were isolated from the leaves of Goniothalamus gracilipes (Annonaceae). Their structures were determined by analyses of MS and 2D NMR data. The absolute configurations of 1 were established by analysis of X-ray diffraction data. Cytotoxic evaluation of the compounds 1-5 against four cancer cell lines (KB, LU-1, HepG-2 and MCF-7) indicated that compound 5 had inhibitory activity against HepG-2 cell line with IC50 value of 16.7 µM. All new compounds (1-5) were evaluated for their antimicrobial activity against a panel of clinically significant microorganisms. Compound 2 showed significant antimicrobial effect on Staphylococus aureus with MIC value of 32 µg/mL.

Antimicrobial lavandulylated flavonoids from a sponge-derived actinomycete.

Analysis of an antimicrobial culture broth extract of the sponge-derived actinomycete Streptomyces sp. (strain G246) led to the isolation of two new lavandulylated flavonoids, 6-lavandulyl-7-methoxy-5,2',4'-trihydroxylflavanone (1) and 5'-lavandulyl-4'-methoxy-2,4,2',6'-tetrahydroxylchalcone (2), along with eight known compounds 3-10. Their structures were established by spectral data analysis, including MS, 1D, 2D-NMR and CD. The absolute configurations of 1 and 2 were suggested by comparison of their experimental and calculated electronic circular dichroism spectra. All the isolated compounds were evaluated for their antimicrobial activity against a panel of clinically significant microorganisms. Compounds 1 and 2 had a broad-spectrum of antimicrobial activity. Additionally, except the strain Escherichia coli, compound 2 exhibited remarkable inhibitory activity against Pseudomonas aeruginosa, Salmonella enterica, Enterococcus faecalis, Staphylococcus aureus, Bacillus cereus, and Candida albicans strains.

Cytotoxic lignans from fruits of Cleistanthus tonkinensis.

Seven new lignans, cleistonkinins A- E (1-5), cleistonkisides A and B (6-7) were isolated from the fruits of Cleistanthus tonkinensis (Euphorbiaceae), together with five known aryltetralin lignans, cleisindoside B (8), cleistantoxin (9), cleisindoside D (10), neocleistantoxin (11) and polygamain (12). Their structures were established from spectral analysis, including mass spectrometry and 2D-NMR. The absolute configurations of 4-7 were determined by analysis of their experimental CD spectra and comparison with calculated electronic circular dichroism (ECD) spectra. Compounds 2 and 6 had selective inhibition with moderate cytotoxicity against Pan C1 and A549 cell lines, respectively. Cleistantoxin (9) was significantly active against A549, HeLa, Hep3B, Pan C1 and MCF7 cell lines while it was less cytotoxic against HeLa cells. Neocleistantoxin (11) exhibited remarkable inhibition toward A549, HeLa, MCF7 and Pan C1. This is the first report for cytotoxicity of 9 and 11 against A549, Hep3B and Pan C1 cell lines.

Cytotoxic Phenolic Compounds from Fruit Glandular Trichomes of Macaranga tanarius.

A new flavonoid, macatanarin D (1), together with five known stilbenes (2-6), was isolated from fruit glandular trichomes of Macaranga tanarius. Their structures were elucidated on the basis of spectroscopic methods and through comparison with data reported in the literature. All isolated compounds were evaluated for their cytotoxic activities against KB and MCF-7 cell lines. Compounds 3, 4, and 5 showed the strongest activities against both cell lines with IC50 values in the range of 0.03-0.12 µM, and compound 2 only showed a significant cytotoxicity against KB cell line (IC50 = 0.26 µM) and a moderate cytotoxicity against MCF-7 (IC50 = 10.4 µM). Compounds 1 and 6 showed weak cytotoxic activities against KB cell line with IC50 values of 29.3 and 24.7 µM, respectively.

Cytotoxic Alkaloids from Leaves of Pilea aff. martinii.

Two new phenanthroquinolizidine alkaloids (1: and 2: ) and a new piperidine derivative (3: ) were isolated from the leaves of Pilea aff. martinii together with 3 known alkaloids: julandine (4: ), cryptopleurine (5: ), and 1,3,6,6-tetramethyl-5,6,7,8-tetrahydro-isoquinolin-8-one (6: ). Their structures were determined by spectral data analyses including mass spectrometry and 2-dimensional nuclear magnetic resonance data. The absolute configurations of 1: -3: were established by comparison of their experimental circular dichroism data with the calculated electronic circular dichroism spectra. The isolated compounds were evaluated for their cytotoxicity against 4 cancer cell lines: KB (mouth epidermal carcinoma cells), HepG-2 (human liver hepatocellular carcinoma cells), LU-1 (human lung adenocarcinoma cells), and MCF-7 (human breast cancer cells). The new phenanthroquinolizidine pileamartine D (2: ) showed strong and selective proliferation inhibition toward KB and HepG-2 cells with IC50 values of 25 and 27 nM, respectively. Pileamartine C (1: ), julandine (4: ), and cryptopleurine (5: ) exhibited cytotoxicity against 4 tested cancer cell lines with IC50 values less than 1 µM.

New 9α-Hydroxy-5α,6α-epoxyhydroxysterols from the Vietnamese Marine Sponge Ircinia echinata.

Chemical investigation of the methanol extract of the Vietnamese marine sponge Ircinia echinata led to the isolation of six new 9α-hydroxy-5α,6α-epoxysterols: 5α,6α-epoxycholesta-7,22(E)-dien-3ß,9α-diol (1), 5α,6α-epoxycholesta-7,24(28)-dien-3ß,9α-diol (2), (24R)-5α,6α-epoxy-24-ethyl-cholesta-7-en-3ß,9α-diol (3), 5α,6α-epoxycholesta-7-en-3ß,9α-diol (4), (24S)-5α,6α-epoxyergosta-7,22-dien-3ß,9α-diol (5), and (24R)-5α,6α-epoxy-24-methyl-cholesta-7-en-3ß,9α-diol (6) along with the known 5α-6α-epoxysterols: 5α,6α-epoxystigmasta-7-en-3ß-ol (7), 5α,6α-epoxystigmasta-7,22-dien-3ß-ol (8), and 5α,6α-epoxyergosta-7-en-3ß-ol (9). Their structures and their configurations were established on the basis of high resolution mass spectra and extensive 1D and 2D NMR spectroscopic data and by comparison with the literature. Their cytotoxic activity, evaluated against three human cancer cell lines, MCF-7, Hep-G2 and LU-1, revealed that only compounds 3 and 4 exhibited significant antiproliferative activity and compound 3 showed a selective inhibition towards the MCF-7 human breast cancer cells.

Cytotoxic dammarane-type triterpenoids from the leaves of Viburnum sambucinum.

Four new dammarane-type triterpenoids (1-4) and twelve known compounds (5-16) were isolated from the leaves of Viburnum sambucinum Reinw. ex Blume. Their structures were determined by spectral data analysis, including MS and 2D NMR. Cytotoxic activity evaluation in vitro against four cancer cell lines (KB, LU-1, HepG2 and MCF7) suggested that the octanor-dammarane derivatives were the main cytotoxic components of the leaves of V. sambucinum.

Design, synthesis and cytotoxicity of bengamide analogues and their epimers.

Starting from d-glycero-d-gulo-heptonic acid γ-lactone and amino acids, a number of diastereoisomeric bengamide analogues were synthesized. Optimization of the reaction conditions revealed that microwave irradiation assistance is a powerful method for the preparation of aminolactams, as well as for the coupling reactions of the lactone 5 with aminolactams. Cytotoxic activity evaluation against six cancer cell lines (KB, HepG2, LU1, MCF7, HL60, and Hela) demonstrated that the configuration of C-2' seems to be critical for the cytotoxic activity of compounds 8b (2'R) and 8a (2'S). Additionally, comparison of cytotoxicity of the protected acetonide compounds with that of their corresponding deprotected bengamide analogues suggested that the flexibility of the ketide side chain should be required for their cytotoxic activity.

Endiandric acid analogues from Beilschmiedia ferruginea as dual inhibitors of Bcl-xL/Bak and Mcl-1/Bid interactions.

A rapid screening by (1)H and (1)H-(13)C HSQC NMR spectroscopy of EtOAc extracts of Endiandra and Beilschmiedia species allowed the selection of Beilschmiedia ferruginea leaves and flowers extract for a chemical investigation, leading to the isolation of 11 new tetracyclic endiandric acid analogues, named ferrugineic acids A-K (1-11). Their structures were determined by 1D and 2D NMR spectroscopic analysis in combination with HRMS data. These compounds were assayed for Bcl-xL and Mcl-1 binding affinities. Ferrugineic acids B, C, and J (2, 3, and 10) exhibited significant binding affinity for both antiapoptotic proteins Bcl-xL (Ki = 19.2, 12.6, and 19.4 µM, respectively) and Mcl-1 (Ki = 14.0, 13.0, and 5.2 µM, respectively), and ferrugineic acid D (4) showed only significant inhibiting activity for Mcl-1 (Ki = 5.9 µM).

Cytotoxic aryltetralin lignans from fruits of Cleistanthus indochinensis.

Eight new aryltetralin lignans, cleisindosides A-F (1-6), picroburseranin (7), and 7-hydroxypicropolygamain (8), were isolated from the fruits of Cleistanthus indochinensis (Euphorbiaceae). The structures of the isolates were established on the basis of their one- and two-dimensional NMR spectral data, as well as their mass spectrometric data. Compound 7 was found to have potent cytotoxicity against oral epidermoid carcinoma cells with an IC50 value of 0.062 µM, whereas glycosylation to 3 (IC50 7.5 µM) and stereochemical changes to 8 (IC50 10.8 µM) led to marked decreases in biological activity. Thus, it was determined that the C-7 and C-8' positions are critical for the biological activity of the lignans from this plant.

Acetylcholinesterase inhibitors from the leaves of Macaranga kurzii.

Bioassay-guided fractionation of an extract of leaves of Macaranga kurzii yielded four new compounds, a stilbene (furanokurzin, 1) and three flavonoids (macakurzin A-C, 2-4). Nine known compounds were also isolated (5-13). Their structures were determined by spectroscopic analyses including MS and 2D NMR. The isolates were all evaluated for acetylcholinesterase inhibitory activity. Compound 6 (trans-3,5-dimethoxystilbene) exhibited the greatest activity (IC50 9 µM). Cytotoxic evaluation against KB cells showed that compound 7 had an IC50 of 4 µM, followed by 11 (IC50 10 µM) and 3 (IC50 13 µM).

Triterpenoid saponins from Symplocos lancifolia.

Three new bidesmosidic saponins (1-3) and a new ursane triterpenoid, 2α,3ß,11α,23-tetrahydroxyurs-12-en-28-oic acid (4), along with seven known compounds, were isolated from a methanolic extract of the leaves of Symplocos lancifolia. The bidesmosidic saponins were found to possess the same sugar unit part, composed of two ß-d-glucose moieties and one α-l-rhamnose moiety, linked to maslinic acid, arjunolic acid, and asiatic acid, respectively. Their structures were elucidated by interpretation of their 1D and 2D NMR spectra and completed by analysis of the HRESIMS data. The antibacterial activity of the isolated triterpenoids was evaluated against Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, and Pseudomonas aeruginosa, and several showed activity against Gram-positive bacteria.

Design, synthesis, and cytotoxic activity of Michael acceptors and enol esters in the benzo[b]acronycine series.

A series of 2-acyl-6-methoxy-3,3,14-trimethyl-3,14-dihydro-7H-benzo[b]pyrano[3,2-h]acridin-7-ones (4-6) was prepared by treatment of 6-methoxy-3,3,14-trimethyl-3,14-dihydro-7H-benzo[b]pyrano[3,2-h]acridin-7-one (3) with an excess of an appropriate acyl chloride in the presence of aluminum chloride. Treatment of (+/-)-cis-1-hydroxy-2-acyloxy-6-methoxy-3,3,14-trimethyl-1,2,3,14-tetrahydro-7H-benzo[b]pyrano[3,2-h]acridin-7-ones (9, 10) or (+/-)-cis-1,2-diacyloxy-6-methoxy-3,3,14-trimethyl-1,2,3,14-tetrahydro-7H-benzo[b]pyrano[3,2-h]acridin-7-ones (2, 11) with hydrochloric acid gave the corresponding 2-acyloxy-6-methoxy-3,3,14-trimethyl-3,14-dihydro-7H-benzo[b]pyrano[3,2-h]acridin-7-ones, exemplified by acetate 7 and butyrate 8. None of the Michael acceptors 4-6 showed significant antiproliferative activity. Enol esters 7 and 8 were markedly cytotoxic toward L1210 leukemia cells, with IC50 values within the same range of magnitude as (+/-)-cis-1,2-diacetoxy-6-methoxy-3,3,14-trimethyl-1,2,3,14-tetrahydro-7H-benzo[b]pyrano[3,2-h]acridin-7-one (S23906-1), currently under phase I clinical trials. In contrast with S23906-1, enol esters 7 and 8 were not reactive toward purified DNA.

Synthesis and cytotoxic and antitumor activity of 1,2-dihydroxy-1,2-dihydrobenzo[b]acronycine diacid hemiesters and carbamates.

A series of cis-1,2-dihydroxy-1,2-dihydrobenzo[b]acronycine diacid hemiesters and dicarbamates were prepared by acylation of cis-1,2-dihydroxy-6-methoxy-3,3,14-trimethyl-1,2,3,14-tetrahydro-7H-benzo[b]pyrano[3,2-h]acridin-7-one. The cytotoxicity of the dicarbamates depended on the steric hindrance of the esterifying groups at positions 1 and 2. Diacid hemiesters displayed significant in vitro cytotoxic activities and induced cell cycle perturbations similar to those obtained with cis-1,2-diacetoxy-1,2-dihydrobenzo[b]acronycine (S23906-1) currently under preclinical development. cis-1-Acetoxy-2-hemiglutaryloxy-1,2-dihydrobenzo[b]acronycine was the most promizing compound of the series, inducing complete inhibition of tumor growth when tested against C38 colon adenocarcinoma implanted in mice.

A transesterification reaction is implicated in the covalent binding of benzo[b]acronycine anticancer agents with DNA and glutathion.

The benzo[b]acronycine derivative S23906-1 has been recently identified as a promising antitumor agent, showing remarkable in vivo activities against a panel of solid tumors. The anticancer activity is attributed to the capacity of the drug to alkylate DNA, selectively at the exocyclic 2-amino group of guanine residues. Hydrolysis of the C-1 and C-2 acetate groups of S23906-1 provides the diol compound S28907-1 which is inactive whereas the intermediate C-2 monoacetate derivative S28687-1 is both highly reactive toward DNA and cytotoxic. The reactivity of this later compound S28687-1 toward two bionucleophiles, DNA and the tripeptide glutathion, has been investigated by mass spectrometry to identify the nature of the (type II) covalent adducts characterized by the loss of the acetate group at position 2. On the basis of NMR and molecular modeling analyses, the reaction mechanism is explained by a transesterification process where the acetate leaving group is transferred from position C-2 to C-1. Altogether, the study validates the reaction scheme of benzo[b]acronycine derivative with its target.