Optimized plant compound with potent anti-biofilm activity across gram-negative species.

Many human diseases, including cystic fibrosis lung infections, are caused or exacerbated by bacterial biofilms. Specialized modes of motility, including swarming and twitching, allow gram-negative bacteria to spread across surfaces and form biofilms. Compounds that inhibit these motilities could slow the spread of biofilms, thereby allowing antibiotics to work better. We previously demonstrated that a set of plant-derived triterpenes, including oleanolic acid and ursolic acid, inhibit formation of Escherichia coli and Pseudomonas aeruginosa biofilms, and alter expression of genes involved in chemotaxis and motility. In the present study, we have prepared a series of analogs of oleanolic acid. The analogs were evaluated against clinical isolates of E. coli and P. aeruginosa in biofilm formation assays and swarming assays. From these analogs, compound 9 was selected as a lead compound for further development. Compound 9 inhibits E. coli biofilm formation at 4 µg/mL; it also inhibits swarming at ≤1 µg/mL across multiple clinical isolates of P. aeruginosa, E. coli, Burkholderia cepacia, and Salmonella enterica, and at <0.5 µg/mL against multiple agricultural strains. Compound 9 also potentiates the activity of the antibiotics tobramycin and colistin against swarming P. aeruginosa; this is notable, as tobramycin and colistin are inhaled antibiotics commonly used to treat P. aeruginosa lung infections in people with cystic fibrosis. qPCR experiments suggested that 9 alters expression of genes involved in regulating Type IV pili; western blots confirmed that expression of Type IV pili components PilA and PilY1 decreases in P. aeruginosa in the presence of 9.

Bifidenone: Structure-Activity Relationship and Advanced Preclinical Candidate.

Bifidenone is a novel natural tubulin polymerization inhibitor that exhibits antiproliferative activity against a range of human cancer cell lines, making it an attractive candidate for development. A synthetic route was previously developed to alleviate supply constraints arising from its isolation in microgram quantities from a Gabonese tree. Using that previously published route, we present here 42 analogues that were synthesized to examine the structure-activity relationship of bifidenone derivatives. In addition to in vitro cytotoxicity data, data from murine xenograft and pharmacokinetic studies were used to evaluate the analogues. Compounds 45b and 46b were found to demonstrate promising efficacy in murine xenograft experiments, and 46b had significantly more potent in vitro antiproliferative activity against taxane-resistant cell lines compared to that of paclitaxel.

Isolation and Identification of the Novel Tubulin Polymerization Inhibitor Bifidenone.

The pursuit of structurally novel compounds has led to the isolation of a series of neolignans (2-6), for which the structures have been determined from microgram quantities using microcryoprobe NMR technology. Compounds 2-6 provided some unexpectedly clear structure-activity relationship data, with compound 2 demonstrating significantly more potency in the in vitro cytotoxicity assay than the other analogues. Further screening found that compound 2 induces apoptosis with activation of caspase 3/7. The NCI Compare algorithm suggested that compound 2 acts through the inhibition of tubulin/microtubule dynamics. Compound 2 was confirmed to be a tubulin polymerization inhibitor that binds directly to tubulin.

Digging Deep for New Compounds from the Compass Plant, Silphium laciniatum.

The compass plant, Silphium laciniatum, is an iconic perennial plant of the North American tallgrass prairie. The plants of the tallgrass prairie historically have been subjected to a number of biological and environmental stresses. Among the adaptations developed by S. laciniatum is a large deep taproot. An investigation of the secondary metabolites found in the root of a S. laciniatum specimen has led to the identification of 15 new terpenoids (3-8, 10-17, and 22), which were screened for cytotoxic activity in the NCI-H460 human large-cell lung carcinoma cell line.

Antibacterial activity of Taxodium ascendens diterpenes against methicillin-resistant Staphylococcus aureus.

One new and seven known diterpenes were identified from an antibacterial chromatographic fraction of Taxodium ascendens. Of these, demethylcryptojaponol (2), 6-hydroxysalvinolone (3), hydroxyferruginol (4), and hinokiol (5) demonstrated potent activity against clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA). These compounds represent a class of synthetically accessible compounds that could be further developed for treatment of drug-resistant bacterial infections.

Diterpenes from the endangered goldenrod Solidago shortii.

Species extinction is tantamount to loss of chemical diversity, and so it is important to seize all opportunities to study species on the brink of extinction. Such studies are often hampered by the limited material available, but that obstacle is surmountable through collaboration with botanical gardens and advances in instrumentation. The goldenrod Solidago shortii is one example of an endangered species native to the United States. From S. shortii, one known diterpene (1), two new diterpenes (2 and 3), and three new hydrolysis products (4-6) are described. This work was made possible through collaboration with the Missouri Botanical Garden and with the use of highly sensitive microcryoprobe NMR technology for structure elucidation and VCD spectroscopy for the determination of absolute configuration.

Antibacterial chromene and chromane stilbenoids from Hymenocardia acida.

Six chromene stilbenoids and one chromane stilbenoid were isolated from the African tree Hymenocardia acida. Several were moderately active against methicillin-resistant Staphylococcus aureus clinical isolate MRSA-108, including hymenocardichromanic acid, which was active at 8 µg/ml. None had IC50 values <20 µM in antiproliferation assays against several human cancer cell lines.

Acetylated dammarane-type bisdesmosides from Combretum inflatum.

The first study of the chemical constituents of Combretum inflatum has resulted in the isolation of seven new acetylated dammarane-type bisdesmosides (1-7). Their structures were determined from microgram quantities on hand using Bruker BioSpin TCI 1.7 mm MicroCryoProbe technology, ESIMS, and comparison to data found in the literature. Compounds 1-7 were screened for inhibition of an Escherichia coli strain UTI89 biofilm, MRSA inhibition, and cytotoxicity in NCI-H460 human lung cancer cells. Compounds 3-7 reduced the growth of MRSA at 16 µg/mL by 71-45%, and compound 7 had an IC50 value of 3.9 µM in NCI-H460.

Phenylpropanoids from Phragmipedium calurum and their antiproliferative activity.

Seven stilbenes and one alkylresorcinol were isolated from the orchid Phragmipedium calurum during a screen for anticancer compounds. They were evaluated for antiproliferative activity against multiple human cancer cell lines, and two displayed moderate activity against several cell lines.

Cytotoxic and antibacterial beilschmiedic acids from a Gabonese species of Beilschmiedia.

High-throughput natural products chemistry methods have facilitated the isolation of eight new (1-8) and two known (9 and 10) beilschmiedic acid derivatives from the leaves of a Gabonese species of Beilschmiedia. Compounds 3-10 were isolated in microgram quantities, and the NMR data for structure elucidation and dereplication were acquired utilizing a Bruker BioSpin TCI 1.7 mm MicroCryoProbe. All of the compounds were screened for cytotoxic and antibacterial activity against NCI-H460 human lung cancer cells and a clinical isolate of methicillin-resistant Staphylococcus aureus, respectively. This is the first report of cytotoxic activity for the endiandric/beilschmiedic acid class of compounds.

Isolation of apoptosis-inducing stilbenoids from four members of the Orchidaceae family.

High-throughput natural product research produced a suite of anticancer hits among several species of the Orchidaceae family (Oncidium microchilum, O. isthmi, and Myrmecophila humboldtii). A commercial Oncidium sp. was also examined as a convenient source of additional material. Isolation and structure elucidation led to the identification of fifteen stilbenoids including a new phenanthraquinone and two new dihydrostilbenes. NMR data for structure elucidation and dereplication were acquired utilizing a Bruker BioSpin TCI 1.7-mm MicroCryoProbe or a 5-µL CapNMR capillary microcoil. Several compounds inhibited proliferation of NCI-H460 and M14 cancer cell lines. All compounds were also examined for their ability to induce apoptosis. Apoptosis induction was determined by measuring caspase 3/7 activation and LDH release in a NCI-H460 cell line. Based on these results, a portion of the extract from a commercially available Oncidium sp. was chemically modified in an attempt to obtain additional phenanthraquinones.

Polyoxygenated cyclohexene derivatives from Monanthotaxis congoensis.

A phytochemical investigation of Monanthotaxis congoensis afforded eight polyoxygenated cyclohexenes as well as the known crotepoxide. Structures were determined using NMR, MS, and optical rotation analyses. One compound displayed moderate antiproliferative activity against NCI-H460 and M14 cancer cells.

Abronione, a rotenoid from the desert annual Abronia villosa.

A high-throughput phytochemical investigation of Abronia villosa afforded a new rotenoid designated abronione (1) along with the known compounds boeravinone C and lupeol. The structure of 1 was determined using NMR, MS, and optical analysis with < 400 µg of material. Compound 1 displayed moderate cytotoxicity against NCI-H460 and HL-60 human cancer cell lines with IC(50) values of 14 and 36 µM, respectively.

Antibiotic indole sesquiterpene alkaloid from Greenwayodendron suaveolens with a new natural product framework.

High-throughput natural products chemistry methods have led to the isolation of three new (1-3) and two known indole sesquiterpene alkaloids (4, 5) from Greenwayodendron suaveolens. Their structures were determined using CapNMR and MS. Pentacyclindole (1) was determined to possess a new natural product framework. Pentacyclindole (1) and polyalthenol (4) showed activity against clinical isolates of Staphylococcus aureus with polyalthenol (4) demonstrating a MIC(90) of 4 microg/mL.

Antibiofilm phenylethanoid glycosides from Penstemon centranthifolius.

Bioassay-guided fractionation of the antibacterial ethyl acetate-ethanol (50 : 50) extract obtained from the aerial parts of Penstemon centranthifolius led to the isolation of six phenylethanoid glycosides (1-6) and eleven iridoid glycosides (7-17). Their structures were determined on the basis of spectroscopic analysis and comparison with the literature. Among them, two phenylethanoid glycosides, 4'''-O-acetylverbascoside (1) and verbascoside (2), were found to show significant inhibition of the formation of bacterial biofilms by Escherichia coli UTI89. Compound 1 showed 77% biofilm inhibition at 2.5 microg/mL, and compound 2 showed 60% inhibition at 5 microg/mL.

Antibacterial clerodane diterpenes from Goldenrod (Solidago virgaurea).

Nine clerodane diterpenes, solidagoic acids C-I (1-7), cleroda-3,13(14)-dien-16,15:18,19-diolide (8) and cleroda-3,13(14)-dien-15,16:18,19-diolide (9) were isolated and characterised from the ethanol-ethyl acetate (1:1) extract of Solidago virgaurea. The structures were determined by NMR spectroscopic analysis. Several displayed moderate antibacterial activity against Staphylococcus aureus.