Antibacterial Sesquiterpene Lactones from Kaunia lasiophthalma.

Phytochemical study of the species Kaunia lasiophthalma enabled the isolation of three undescribed and three known guaianolide-type sesquiterpene lactones, and one new benzofuran. The bioguided fractionation methodology was successful in detecting antimicrobial metabolites against Staphylococcus aureus strains and permitted the description of undescribed guaianolide-type sesquiterpene lactones with substitution patterns matching all those described in the Oxylobinae subtribe.

Expanding Diterpene Complexity and Diversity via Photoinduced Ring Distortions.

Natural products and their semi-synthetic derivatives undoubtedly constitute an important source of therapeutic agents. Their importance lies in their own origin and evolution, since they have great chemical diversity, biochemical specificity, and pharmacological properties. Currently, there is a renewed interest in the development of methodologies capable of efficiently modifying the chemical structure of these bioactive platforms. In this work, the photoderivatization of the diterpene solidagenone was performed using a complexity-to-diversity-oriented approach. By exploring [2+2]-photocycloaddition, photoinduced-hydrogen abstraction, and photoxygenation reactions, a set of solidagenone derivatives was obtained, showing different ring fusions, side chain rearrangements, and modifications of the original furan ring's substitution pattern. The derivatives obtained were characterised by NMR methodologies. To evaluate the structural diversity of the labdane-derived compounds, their physicochemical properties, structural similarity, and chemical space were analysed. These results suggest that photochemical reactions are a useful tool for performing ring distortion transformations, generating derivatives of natural compounds with wide diversity, structural complexity, and with potential biological properties.

Antibacterial activity of withanolides and their structure-activity relationship.

Two new withanolides, (17R,20S,22R)-4ß-acetoxy-5ß,6ß-epoxy-19,27-dihydroxy-1-oxo-witha-2,24-dienolide (withalongolide A 4-acetate (5) and (17R,20S,22R)-5ß,6ß-epoxy-27-hydroxy-1,4-dioxo-witha-24-enolide (9), and seven known withanolides with normal structure (1-4, 6-8) were isolated from aerial parts of Cuatresia colombiana. Several semisynthetic derivatives were prepared from the natural metabolites withaferin A and jaborosalactone 38. The compounds were fully characterized by a combination of spectroscopic methods (1D and 2D NMR and MS). The compounds isolated from C. colombiana, sixteen withanolides previously isolated from different Solanaceae species with different skeletons and semisynthetic derivatives were evaluated for their antibacterial activity against a selected panel of Gram-positive and Gram-negative bacteria. According to the bioactivity against S. aureus and E. faecalis, the compounds evaluated were divided into three groups: compounds with high activity (MIC 0.063 mM), compounds with moderate activity (0.5 mM > MIC > 0.125 mM) and non-active compounds (MIC ≥1 mM); in addition, some structure-activity relationship keys could be inferred.

Identification of potential biological target for trypanocidal sesquiterpene lactones derivatives.

Sesquiterpene lactones are natural products of the Asteraceae family that have shown trypanocidal activity against Trypanosoma cruzi, even exceeding the effectiveness of drugs used in the treatment of American trypanosomiasis. However, there is no agreement on their mechanism of action and their specificity to interact with parasite proteins. For this reason, we aimed to find biological targets that can interact with these compounds by reverse virtual screening with ligand pharmacophores and putative binding sites and the use of bioinformatic databases. Therefore, 41 possible biological targets were found, and four of them (with crystallized proteins), interfering directly or indirectly in the trypanosomatid redox system, were studied in detail. As a first approach, we focused on the study of trypanothione reductase, and protein-ligand interaction fingerprint analyses were performed to find binding site determinants that promote a possible inhibition of the enzyme. This study contributes to the understanding of one of the putative mechanisms of action of sesquiterpene lactones on one of the numerous suggested targets.Communicated by Ramaswamy H. Sarma.

Deoxycytidine kinase (dCK) inhibition is synthetic lethal with BRCA2 deficiency.

BRCA2 is a well-established cancer driver in several human malignancies. While the remarkable success of PARP inhibitors proved the clinical potential of targeting BRCA deficiencies, the emergence of resistance mechanisms underscores the importance of seeking novel Synthetic Lethal (SL) targets for future drug development efforts. In this work, we performed a BRCA2-centric SL screen with a collection of plant-derived compounds from South America. We identified the steroidal alkaloid Solanocapsine as a selective SL inducer, and we were able to substantially increase its potency by deriving multiple analogs. The use of two complementary chemoproteomic approaches led to the identification of the nucleotide salvage pathway enzyme deoxycytidine kinase (dCK) as Solanocapsine's target responsible for its BRCA2-linked SL induction. Additional confirmatory evidence was obtained by using the highly specific dCK inhibitor (DI-87), which induces SL in multiple BRCA2-deficient and KO contexts. Interestingly, dCK-induced SL is mechanistically different from the one induced by PARP inhibitors. dCK inhibition generates substantially lower levels of DNA damage, and cytotoxic phenotypes are associated exclusively with mitosis, thus suggesting that the fine-tuning of nucleotide supply in mitosis is critical for the survival of BRCA2-deficient cells. Moreover, by using a xenograft model of contralateral tumors, we show that dCK impairment suffices to trigger SL in-vivo. Taken together, our findings unveil dCK as a promising new target for BRCA2-deficient cancers, thus setting the ground for future therapeutic alternatives to PARP inhibitors.

Selective extraction of antimicrobial agents from Jodina rhombifolia by supercritical fluid carbon dioxide: phytochemical profile.

The goals of this study were to determine the phytochemical profile of Jodina rhombifolia and to evaluate the ability of supercritical fluids (ScFCO2) to selectively extract the metabolites responsible for the bioactivity. This species has simple aromatic compounds and lignan monomers, as well as glycerides containing epoxidized saturated fatty acids. Regarding the extraction by ScFCO2, the extracts showed a higher antimicrobial activity against human pathogenic strains, with respect to the ethanolic extracts obtained from plant residues after extraction by ScFCO2. Furthermore, the bioactive compounds were concentrated in just 1% P/P of the weight of the dry plant material. Extraction by ScFCO2 was carried out under different conditions of pressure and temperature, with the best results being obtained at 30 °C and 30 MPa. The results obtained demonstrate the advantages of ScFCO2 extractions over classical solvent extractions, in terms of improved safety and the ability to selectively extract the compounds of interest.

Psilostachyins as trypanocidal compounds: Bioguided fractionation of Ambrosia tenuifolia chemically modified extract.

This work focusses on the chemical diversification of an Ambrosia tenuifolia extract and its bioguided fractionation, aiming to unveil the chemical entity responsible for the trypanocidal activity. Besides, a revision of the phytochemical study of this species, based on previous reports of the antiparasitic psilostachyins A and C as main compounds, was conducted. To improve the biological properties of a plant extract through a simple chemical reaction, the oxidative diversification of the dichloromethane extract of this plant species was carried out. A bioguided fractionation of a chemically modified extract was performed by evaluating the inhibitory activity against Trypanosoma cruzi trypomastigotes. This experiment led to the isolation of one of the most active compounds. In general terms, epoxidized metabolites were obtained as a result of the oxidation of the major metabolite of the species. The trypanocidal activity of some tested metabolites overperformed the reference drug, benznidazole, displaying no cytotoxicity at trypanocidal concentrations. Key structure-activity relationships were obtained for designing previously undescribed antiparasitic sesquiterpene lactones.

Withanolides from the genus Exodeconus (Solanaceae). Chemotaxonomical considerations.

Five Exodeconus species were phytochemically analyzed. From the aerial parts of E. pusillus, the 7α,27-dihydroxy-1-oxo-22R-witha-2,5,24-trienolide and three other previously unreported normal-type withanolides were isolated. All the studied species had normal type and/or ring-D aromatic withanolides, and some had already been isolated from other Solanaceae genera, and therefore, these compounds are not chemotaxonomic markers at the generic level. The chemical composition of an undescribed Exodeconus species analyzed here supports the designation of this taxon as a new entity. The integral chemical profile of Exodeconus can be evaluated for its taxonomic implication when a more robust phylogeny of Solanaceae is available that allows the phylogenetic relationships with its closest genera to be clarified.

Synthetic Lethal Activity of Benzophenanthridine Alkaloids From Zanthoxylum coco Against BRCA1-Deficient Cancer Cells.

Several plants from South America show strong antitumoral properties based on anti-proliferative and/or pro-apoptotic activities. In this work we aimed to identify selective cytotoxic compounds that target BRCA1-deficient cancer cells by Synthetic Lethality (SL) induction. Using a high-throughput screening technology developed in our laboratory, we analyzed a collection of extracts from 46 native plant species from Argentina using a wide dose-response scheme. A highly selective SL-induction capacity was found in an alkaloidal extract from Zanthoxylum coco (Fam. Rutaceae). Bio-guided fractionation coupled to HPLC led to the identification of active benzophenanthridine alkaloids. The most potent SL activity was found with the compound oxynitidine, which showed a remarkably low relative abundance in the active fractions. Further validation experiments were performed using the commercially available and closely related analog nitidine, which showed SL-induction activity against various BRCA1-deficient cell lines with different genetic backgrounds, even in the nanomolar range. Exploration of the underlying mechanism of action using BRCA1-KO cells revealed AKT and topoisomerases as the potential targets responsible of nitidine-triggered SL-induction. Taken together, our findings expose an unforeseen therapeutic activity of alkaloids from Zanthoxylum-spp. that position them as novel lead molecules for drug discovery.

Selective Antiproliferative Withanolides from Species in the Genera Eriolarynx and Deprea.

Four new withanolides (2-5), together with 4ß,7ß,20-trihydroxy-1-oxowitha-2,5,24-trienolide (1), were isolated from the aerial parts of Eriolarynx iochromoides. The antiproliferative activity of all compounds purified from E. iochromoides together with four withaphysalins and four physangulidines isolated previously from three Deprea species were evaluated against human solid tumor cell lines. Four withanolides showed antiproliferative activity comparable in potency to cisplatin. Selectivity toward cancer cells and interaction with P-glycoprotein of the active withanolides were evaluated.

Clinanthus microstephium, an Amaryllidaceae Species with Cholinesterase Inhibitor Alkaloids: Structure-Activity Analysis of Haemanthamine Skeleton Derivatives.

Plants of the Amaryllidaceae family are well-known (not only) for their ornamental value but also for the alkaloids that they produce. In this report, the first phytochemical study of Clinanthus genus was carried out. The chemical composition of alkaloid fractions from Clinanthus microstephium was analyzed by GC/MS and NMR. Seven known compounds belonging to three structural types of Amaryllidaceae alkaloids were identified. An epimeric mixture of a haemanthamine-type compound (6-hydroxymaritidine) was tested as an inhibitor against acetyl- and butyrylcholinesterase enzymes (AChE and BChE, respectively), two enzymes relevant in the treatment of Alzheimer's disease, with good results. Structure-activity relationships through molecular docking studies with this alkaloid and other structurally related compounds were discussed.

Phytochemical Study of Senecio volckmannii Assisted by CASE-3D with Residual Dipolar Couplings and Isotropic 1H/13C NMR Chemical Shifts.

Nine new eremophilanolides, with seven known sesquiterpenoids, and 4-hydroxyacetophenone were isolated from the aerial parts of Senecio volckmannii var. volckmannii. The structures of these compounds were fully characterized using a combination of spectroscopic techniques including multinuclear and multidimensional NMR and mass spectrometry. The recently published Computer Assisted 3D Structure Elucidation (CASE-3D) protocol was applied in the configurational and conformational analysis of many of these eremophilanolides on the basis of Residual Dipolar Couplings (RDCs) and/or DFT predicted 1H/13C chemical shifts.

Phytochemical Study of the Genus Salpichroa (Solanaceae), Chemotaxonomic Considerations, and Biological Evaluation in Prostate and Breast Cancer Cells.

Twelve Salpichroa taxa have been phytochemically analyzed. From the aerial parts of S. scandens, four known salpichrolides A, C, I, S, and an unreported withanolide named salpichrolide V (1), were isolated. In S. dependens, S. gayi, S. glandulosa subsp. glandulosa, S. glandulosa subps. weddellii, S. leucantha, S. micrantha, S. microloba, S. proboscidea, S. ramosissima, S. tristis var. tristis, and S. weberbauerii, no withanolides were found. The chemical content of ca. 85% of the Salpichroa taxa is in agreement with molecular studies, which suggest that Salpichroa and Jaborosa, a genus considered morphologically close to Salpichroa, are distant in the systematic of the Solanoideae subfamily. Moreover, the in vitro cytotoxic activity of a set of natural salpichrolides and derivatives was examined against two prostate carcinoma cell lines (PC3 and LNCaP) and two human breast cancer cell lines (MCF-7 and T47D). Several compounds showed moderate activity (IC50  = 64.91 - 29.97 µm).

Biotransformation of Salpichrolides A, C, and G by Three Filamentous Fungi.

Incubation of salpichrolide A (1) with Rhizomucor miehei produced hydroxylation in rings B and C (C-7 and C-12) and led to C-5-C-6 epoxide opening, while incubation of salpichrolides C (2) and G (3) with R. miehei led to epoxide opening at the C-24-C-25 and C-5-C-6 positions, respectively. Biotransformation of salpichrolide A (1) with Cunninghamella elegans produced stereoselective hydroxylated, oxidized, and reduced derivatives in different positions of the A, B, and C rings and C-5-C-6 epoxide opening. In addition, selective epoxide opening at the C-5-C-6 or C-24-C-25 positions was obtained from the incubation of salpichrolide A (1) with Curvularia lunata.

Withanolides with antibacterial activity from Nicandra john-tyleriana.

Eleven new withanolides (1-11) were isolated and characterized from the aerial parts of Nicandra john-tyleriana. Five of these withanolides have an unmodified skeleton (1-5), two are acnistins (6, 7), and four are withajardins (8-11). These new isolates were fully characterized using a combination of spectroscopic techniques (including multidimensional NMR) and mass spectrometry. All compounds were evaluated for their antibacterial activity against Bacillus, Enterococcus, Escherichia, Listeria, Pseudomonas, and Staphylococcus strains.

Withanolides from three species of the genus Deprea (Solanaceae). Chemotaxonomical considerations.

Nine withanolides were isolated from the aerial parts of Deprea bitteriana, Depreacuyacensis, and Depreazamorae. D.bitteriana yielded two withaphysalins, D. cuyacensis gave two 13,14-seco withaphysalins, while D. zamorae yielded five physangulidines. The compounds were fully characterized by a combination of spectroscopic methods (1D and 2D NMR and MS). All compounds isolated from D.bitteriana and D. cuyacensis were obtained as epimeric mixtures at C-18. The structure of physangulidine D was confirmed by X-ray diffraction analysis. The skeletons found in this research support the chemotaxonomical position of the genus Deprea in the tribe Physalideae.

Antiproliferative and quinone reductase-inducing activities of withanolides derivatives.

Two new and five known withanolides (jaborosalactones 2, 3, 4, 5, and 24) were isolated from the leaves of Jaborosa runcinata Lam. We also obtained some derivatives from jaborosalactone 5, which resulted to be the major isolated metabolite. The natural compounds as well as derivatives were evaluated for their antiproliferative activity and the induction of quinone reductase 1 (QR1; NQ01) activity. Structure-activity relationships revealed valuable information on the pharmacophore of withanolide-type compounds. Three compounds of this series showed significantly higher antiproliferative activity than jaborosalactone 5. The effect of these compounds on the cell cycle was determined. Furthermore, the ability of major compounds to induce QR1 was evaluated. It was found that all the active test compounds are monofunctional inducers that interact with Keap1. The most promising derivatives prepared from jaborosalactone 5 include (23R)-4ß,12ß,21-trihydroxy-1,22-dioxo-12,23-cycloergostan-2,5,17,24-tetraen-26,23-olide (18) and (23R)-21-acetoxy-12ß-hydroxy-1,22-dioxo-12,23-cycloergostan-2,5,17,24-tetraen-26,23-lactame (20).

Withanolides with phytotoxic activity from two species of the genus Salpichroa: S. origanifolia and S. tristis var. lehmannii.

Seven new withanolides, salpichrolides O-U (1-7), the known 2,3-dihydrosalpichrolide B (9), a substance not previously isolated from a natural source, and three known compounds, salpichrolide D (8), salpichrolide A (10), and salpichrolide C (11), were isolated and characterized from the aerial parts of Salpichroa origanifolia and S. tristis var. lehmannii. Compounds 1-4 and 8 have an oxygenated D ring, while compounds 5-7 and 9-11 possess a six-membered aromatic D ring. The structures of the isolated compounds were identified by analysis of their spectroscopic data including NMR and MS. Withanolides 1, 3, 8, 10, and 11 exhibited selective radicle growth inhibition toward Lactuca sativa (lettuce) at 150 and 400 ppm.

Agarofuran sesquiterpenes from Schaefferia argentinensis.

Sixteen dihydro-ß-agarofuran sesquiterpenes were isolated from the aerial parts of Schaefferia argentinensis Speg. Their structures were determined by a combination of 1D and 2D NMR and MS techniques. The in vitro antiproliferative activity of the major sesquiterpenes was examined in T47D, MCF7, and MDA-MB231 human cancer cell lines, but was found to be marginal.

Antiproliferative activity of withanolide derivatives from Jaborosa cabrerae and Jaborosa reflexa. Chemotaxonomic considerations.

Three withanolides were isolated from the aerial parts of Jaborosa reflexa Phil. Jaborosa cabrerae Barboza yielded five sativolide withanolides (including jaborosalactones R, S, 38, and 39) and two trechonolide withanolides epimeric at C-23 (trechonolide A and jaborosalactone 32). In addition, five derivatives were obtained by chemical derivatization of jaborosalactone 38, and all compounds were fully characterized by 1D and 2D NMR spectroscopic studies. The in vitro antiproliferative activities of the major natural withanolides and the semisynthetic derivatives were examined against HBL-100, HeLa, SW1573, T-47D, and WiDr human solid tumor cancer cell lines. Some chemotaxonomic considerations are discussed.