Synthesis and in vitro cytotoxicity evaluation of ß-carboline-combretastatin carboxamides as apoptosis inducing agents: DNA intercalation and topoisomerase-II inhibition.

To explore a new set of cytotoxic agents, ß-carboline-combretastatin carboxamide conjugates were designed, synthesized and evaluated for their in vitro cytotoxicity potential, DNA binding affinity and Topoisomerase-II (topo-II) inhibition activity. Among the designed hybrids, 10v and 10af have shown significant cytotoxic effect against A549 (lung cancer) cell line having IC50 value 1.01 µM and 1.17 µM respectively. Further, it was speculated that treatment with compound 10v may induce apoptosis among A549 cells, which was supported by Hoechst staining, DCFDA, Annexin V-FITC and morphological assays. Flow cytometric analysis revealed that the hybrid 10v arrests A549 cells in G2/M phase of cell cycle in a dose dependent manner. Amongst the active hybrids, most potent hybrid 10v was tested for DNA topo-II inhibition activity. Moreover, to further support the biological activity and to infer the mode of interaction between ligands and DNA, spectroscopy and molecular docking studies were carried out. The docking and spectroscopy results showed that the ligands exhibited an intercalative mode of binding with DNA and could efficiently bind to DNA and form topo-II ternary complex. Based on these experiments, the hybrids 10v and 10af were identified as proficient new scaffolds which need to be developed as hit molecules for therapeutic interest.

Synthesis of DNA interactive C3-trans-cinnamide linked ß-carboline conjugates as potential cytotoxic and DNA topoisomerase I inhibitors.

A series of new C3-trans-cinnamide linked ß-carboline conjugates has been synthesized by coupling between various ß-carboline amines and substituted cinnamic acids. Evaluation of their anti-proliferative activity against a panel of selected human cancer cell lines such as A549 (lung cancer), MCF-7 (breast cancer), B16 (melanoma), HeLa (cervical cancer) and a normal cell line NIH3T3 (mouse embryonic fibroblast cell line), suggested that the newly designed conjugates are considerably active against all the tested cancer cell lines with IC50 values 13-45 nM. Moreover, the conjugates 8v and 8x were the most active against MCF-7 cells (14.05 nM and 13.84 nM respectively) and also even potent on other cell lines tested. Further, detailed investigations such as cell cycle analysis, apoptosis induction study, topoisomerase I inhibition assay, DNA binding affinity and docking studies revealed that these new conjugates are DNA interactive topoisomerase I inhibitors.

An efficient one-pot approach for the regio- and diastereoselective synthesis of trans-dihydrofuran derivatives: cytotoxicity and DNA-binding studies.

An operationally facile and high yielding one-pot, three-component protocol has been developed for the preparation of selectively trans-2,3-dihydrofuro[3,2-c]coumarins and trans-1,2-dihydrobenzo[h]furo[3,2-c]quinolinones. This protocol proceeds through a domino Knoevenagel condensation, a Michael addition followed by intramolecular SN2 cyclisation. All the synthesized compounds have been evaluated for their in vitro cytotoxic activity against selected human cancer cell lines. Interestingly, most of the compounds have exhibited considerable cytotoxicity with IC50 values <10 µM in all the tested cell lines. Moreover, these compounds showed higher activity against MCF-7 (breast cancer) cell lines compared to other tested cell lines. Compounds 1g and 1r displayed significant cytotoxicity against all four tested cell lines. Cytotoxicity studies indicated that the toxicity of the synthesized compounds was considerably higher in tumor cells compared to normal cells. The structure-activity relationship studies revealed that the activating groups in these compounds preferably improved the activity compared to the deactivating groups. For a better understanding of the mechanism of action of these compounds, we performed the binding studies with calf thymus DNA (CT-DNA). Both molecular docking studies as well as biophysical studies indicate that these compounds may possess DNA binding affinity through intercalation. Through photocleavage studies, it is evident that they have the potential to cleave pBR322 plasmid DNA strands in a concentration and time dependent manner. In addition, compounds 1g and 1r showed significant topoisomerase II inhibitory activities. Moreover, an in silico study of these synthesized compounds revealed that they possess drug-like properties.

Phenacyl azides as efficient intermediates: one-pot synthesis of pyrrolidines and imidazoles.

Phenacyl azides were decomposed in basic media to generate N-unsubstituted imines which were reacted with cyclic amino acids to give an azomethine ylide that underwent [3 + 2] cycloaddition with maleimides and N-unsubstituted imines to yield various diastereoselective pyrrolidines and imidazoles respectively in a one-pot three component manner with good to excellent yields.

Iron-Mediated One-Pot Synthesis of 3,5-Diarylpyridines from ß-Nitrostyrenes.

An operationally simple and mild one-pot protocol for the synthesis of a variety of 3,5-diarylpyridines from ß-nitrostyrenes was achieved by using elemental iron. This reaction proceeds via reduction of the nitro group, resulting in in situ imine formation followed by trimolecular condensation with concomitant debenzylative aromatization. By employing this method, a series of symmetrical and unsymmetrical 3,5-diarylpyridines were synthesized with good to excellent yields. In addition, this method was also utilized for the synthesis of Sch-21418, an anti-inflammatory agent on gram scale.

Design and synthesis of C3-tethered 1,2,3-triazolo-ß-carboline derivatives: Anticancer activity, DNA-binding ability, viscosity and molecular modeling studies.

A series of new DNA-interactive C3-tethered 1,2,3-triazolo-ß-carboline derivatives have been synthesized via 'click' reaction and evaluated for their in vitro cytotoxicity as well as DNA binding affinity. Interestingly, these hybrids have displayed potent in vitro cytotoxicity in comparison to Harmine against the HT-29 (colon cancer) and HGC-27 (gastric cancer) cell lines. The compounds 7f, 7k, 7n and 7s appear to be more effective against the HGC-27 cell line, among which compound 7f showed the highest cytotoxicity (5.44 ± 0.58, IC50 µM). The compounds 7e and 7f appear to be more active against the HT-29 cell line, among which compound 7f exhibited the highest cytotoxicity (3.67 ± 0.62, IC50 µM). To gain more insight into the DNA-binding ability, spectroscopic techniques such as UV-Visible, fluorescence and circular dichroism studies were performed. Viscosity measurements and molecular docking studies substantiate that these compounds indeed bind to DNA via the minor groove.

PhI(OAc)2-mediated one-pot oxidative decarboxylation and aromatization of tetrahydro-ß-carbolines: synthesis of norharmane, harmane, eudistomin U and eudistomin I.

Iodobenzene diacetate was employed as a mild and efficient reagent for one-pot oxidative decarboxylation of tetrahydro-ß-carboline acids and dehydrogenation of tetrahydro-ß-carbolines to access the corresponding aromatic ß-carbolines. To the best of our knowledge this is the first synthesis of ß-carbolines via a one-pot oxidative decarboxylation at ambient temperature. The utility of this protocol has been demonstrated in the synthesis of ß-carboline alkaloids norharmane (2o), harmane (2p), eudistomin U (9) and eudistomin I (12).

Design and synthesis of dithiocarbamate linked ß-carboline derivatives: DNA topoisomerase II inhibition with DNA binding and apoptosis inducing ability.

A series of new ß-carboline-dithiocarbamate derivatives bearing phenyl, dithiocarbamate and H/methyl substitutions at position-1, 3 and 9, respectively, were designed and synthesized. These derivatives 8a-l and 13a-l and their starting precursors (7 a-d and 12 a-d) have been evaluated for their in vitro cytotoxic activity on selected human cancer cell lines. Among the derivatives tested, 7 c, 12 c, 8 a, 8 d, 8 i, 8 j, 8 k, 8l and 13 d-l exhibited considerable cytotoxicity against most of the tested cancer cell lines (IC50<10µM). Interestingly, most of the derivatives (8 a-l and 13a-l) exhibited enhanced activity than their precursors (7 a-d and 12 a-d), which indicates that the combination of dithiocarbamate with ß-carboline enhances the cytotoxicity of 8 a-l and 13 a-l. Moreover, the derivatives 8 j and 13 g exhibited significant cytotoxic activity with IC50 values of 1.34 µM and 0.79 µM on DU-145 cancer cells, respectively. Further, the induction of apoptosis by these derivatives was confirmed by Annexin V-FITC and Hoechst staining assays. However, both biophysical as well as molecular docking studies suggested a combilexin-type of interaction between these derivatives and DNA, unlike simple ß-carbolines. With a view to understand their mechanism of action, DNA topoisomerase II (topo II) inhibition assay was also performed. Overall, the present study emphasizes the importance of linking a dithiocarbamate moiety to the ß-carboline scaffold for exhibiting profound activity.

Dithiocarbamate/piperazine bridged pyrrolobenzodiazepines as DNA-minor groove binders: synthesis, DNA-binding affinity and cytotoxic activity.

A new series of C8-linked dithiocarbamate/piperazine bridged pyrrolo[2,1-c][1,4]benzodiazepine conjugates (5a-c, 6a,b) have been synthesized and evaluated for their cytotoxic potential and DNA-binding ability. The representative conjugates 5a and 5b have been screened for their cytotoxicity against a panel of 60 human cancer cell lines. Compound 5a has shown promising cytotoxic activity on selected cancer cell lines that display melanoma, leukemia, CNS, ovarian, breast and renal cancer phenotypes. The consequence of further replacement of the 3-cyano-3,3-diphenylpropyl 1-piperazinecarbodithioate in 5b and 5c with 4-methylpiperazine-1-carbodithioate yielded new conjugates 6a and 6b respectively. In addition, the compounds 5c and 6a,b have been evaluated for their in vitro cytotoxicity on some of the selected human cancer cell lines and these conjugates have exhibited significant cytotoxic activity. Further, the DNA-binding ability of these new conjugates has been evaluated by using thermal denaturation (ΔTm) studies. The correlation between structure and DNA-binding ability has been investigated by molecular modeling studies which predicted that 6b exhibits superior DNA-binding ability and these are in agreement with the experimental DNA-binding studies.

Synthesis and biological evaluation of benzimidazole-oxindole conjugates as microtubule-targeting agents.

A series of benzimidazole-oxindole conjugates were synthesized and evaluated for their cytotoxic activity. The cytotoxicity assay results suggest that conjugates 5c and 5p exhibit promising cytotoxicity against human breast cancer cell line (MCF-7). The Cell cycle analysis revealed that these conjugates induced cell cycle arrest at G2/M phase in MCF-7 cells. The tubulin polymerization assay results suggested that these conjugates inhibit tubulin polymerization with IC50 values 1.12 and 1.59µM respectively. Immunofluorescence analysis also suggested that these conjugates effectively inhibited the microtubule assembly in MCF-7 cells. Further, molecular docking studies indicated that these conjugates 5c and 5p interact and binds efficiently with the tubulin protein. By and large, the results demonstrated that these benzimidazole-oxindole conjugates possess cytotoxic property by inhibiting the tubulin polymerization.

DNA-binding affinity and anticancer activity of ß-carboline-chalcone conjugates as potential DNA intercalators: Molecular modelling and synthesis.

A new series of DNA-interactive ß-carboline-chalcone conjugates have been synthesized and evaluated for their in vitro cytotoxicity and DNA-binding affinity. It has been observed that most of these new hybrids have shown potent cytotoxic activities on A-549 (lung adenocarcinoma) cell lines with IC50 values lower than 10 µM. The hybrid 7b is more effective against some of the selected cancer cell lines with IC50 values less than 50 µM. In addition, compounds 7e, 7k, 7p-u has displayed significant elevation in ΔTm of DNA in comparison to Adriamycin, suggesting significant interaction and remarkable DNA stabilization. The DNA intercalation of these new hybrids has been investigated by fluorescence titration, DNA viscosity measurements, molecular docking as well as molecular dynamics and the results are in agreement with the thermal denaturation studies.

Asymmetric Michael addition of ketones to nitroolefins: pyrrolidinyl-oxazole-carboxamides as new efficient organocatalysts.

Chiral pyrrolidinyl-oxazole-carboxamides were synthesized and used as efficient new organocatalysts for the asymmetric Michael addition of ketones with nitroalkenes under solvent-free conditions. Gratifyingly, the corresponding Michael adducts were obtained in higher yields (up to 99%) and excellent stereoselectivities (up to >99/1 dr and 99% ee). Transition state models have been proposed to account for the high enantio- and diastereoselectivity of these Michael addition reactions and also the energetics have been investigated using density functional methods. These results support the preferential formation of syn-products by the approach of trans-ß-nitrostyrene through the re-face of anti-enamine.

Recent advancements in sustainable synthesis of zinc oxide nanoparticles using various plant extracts for environmental remediation.

The sustainable synthesis of zinc oxide nanoparticles (ZnO-NPs) using plant extracts has gained significant attention in recent years due to its eco-friendly nature and potential applications in numerous fields. This synthetic approach reduces the reliance on non-renewable resources and eliminates the need for hazardous chemicals, minimizing environmental pollution and human health risks. These ZnO-NPs can be used in environmental remediation applications, such as wastewater treatment or soil remediation, effectively removing pollutants and improving overall ecosystem health. These NPs possess a high surface area and band gap of 3.2 eV, can produce both OH° (hydroxide) and O2-° (superoxide) radicals for the generation of holes (h+) and electrons (e-), resulting in oxidation and reduction of the pollutants in their valence band (VB) and conduction band (CB) resulting in degradation of dyes (95-100% degradation of MB, MO, and RhB dyes), reduction and removal of heavy metal ions (Cu2+, Pb2+, Cr6+, etc.), degradation of pharmaceutical compounds (paracetamol, urea, fluoroquinolone (ciprofloxacin)) using photocatalysis. Here, we review an overview of various plant extracts used for the green synthesis of ZnO NPs and their potential applications in environmental remediation including photocatalysis, adsorption, and heavy metal remediation. This review summarizes the most recent studies and further research perspectives to explore their applications in various fields.

Enantioselective Imine Reduction of Dihydro-ß-carbolines by Fe-Thiosquaramide Catalyst.

Enantioselective imine reduction of dihydro-ß-carbolines (DHBCs) is a reliable and powerful tool to construct bioactive chiral tetrahydro-ß-carbolines (THBCs). Here, we report an efficient enantioselective imine reduction employing in situ generated Fe-thiosquaramides (Fe-TSQs) 3a and 3b as asymmetric organometallic catalysts to produce chiral THBCs (2a-h). The catalyst 3a at 15 mol % was found to be suitable for the substrates with alkyl and aryl groups which afford corresponding chiral THBCs with excellent enantioselectivities (up to ee 99%).

Green Chemistry Based Synthesis of Zinc Oxide Nanoparticles Using Plant Derivatives of Calotropis gigantea (Giant Milkweed) and Its Biological Applications against Various Bacterial and Fungal Pathogens.

Nanotechnology is a burning field of scientific interest for researchers in current era. Diverse plant materials are considered as potential tool in green chemistry based technologies for the synthesis of metal nanoparticles (NPs) to cope with the hazardous effects of synthetic chemicals, leading to severe abiotic climate change issues in today's agriculture. This study aimed to determine the synthesis and characterization of metal-based nanoparticles using extracts of the selected plant Calotropis gigantea and to evaluate the enzyme-inhibition activities and antibacterial and antifungal activity of extracts of metal-based zinc nanoparticles using C. gigantea extracts. The crystal structure and surface morphology were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). C. gigantea was examined for antimicrobial activity against clinical isolates of bacteria and fungi. The water, ethanolic, and acetone extracts of C. gigantea were studied for their antagonistic action against bacterial strains (E. coli, S. aureus, P. multocida, and B. subtilis) and selected fungal strains (A. paracistic, F. solani, A. niger, S. ferrugenium, and R. nigricans). In vitro antimicrobial activity was determined by the disc diffusion method, where C. gigantea wastested for AChE and BChE inhibitory activity using Ellman's methodology. The kinetic analysis was performed by the proverbial Berthelot reaction for urease inhibition. The results showed that out of all the extracts tested, ethanolic and water extracts possessed zinc nanoparticles. These extracts showed the maximum zone of inhibition against F. solani and P. multocida and the lowest against S. ferrugenium and B. subtilis. A potential source of AChE inhibitors is certainly provided by the abundance of plants in nature. Numerous phyto-constituents, such as AChE and BChE inhibitors, have been reported in this communication. Water extract was active and has the potential for in vitro AChE and BChE inhibitory activity. The urease inhibition with flower extracts of C. gigantea revealed zinc nanoparticles in water extracts that competitively inhibited urease enzymes. In the case of cholinesterase enzymes, it was inferred that the water extract and zinc nanoparticles have more potential for inhibition of BChE than AChE and urease inhibition. Furthermore, zinc nanoparticles with water extract are active inthe inhibition of the bacterial strains E. coli, S. aureus, and P. multocida and the fungal strains A. paracistic, F. solani, and A. niger.

Corrigendum: Role of Promising Secondary Metabolites to Confer Resistance Against Environmental Stresses in Crop Plants: Current Scenario and Future Perspectives.

[This corrects the article DOI: 10.3389/fpls.2022.881032.].

Zn alleviated salt toxicity in Solanum lycopersicum L. seedlings by reducing Na+ transfer, improving gas exchange, defense system and Zn contents.

Soil secondary salinization is a serious menace that has significant influence on the sustainability of agriculture and threatens food security around the world. Zinc (Zn) as an essential plant nutrient associated with many physio-biochemical processes in plants and improve resistance against various abiotic stresses. The role of Zn in acclimation of Solanum lycopersicum L. challenged with salt stress is miserly understood. A hydroponic study was performed with two tomato varieties (Riogrande and Sungold) exposed to the salinity stress (0 mM and 160 mM NaCl) under two Zn concentrations (15 µM and 30 µM ZnSO4). The results revealed that salt stress exerted strongly negative impacts on root and shoot length, fresh and dry biomass, plant water relations, membrane stability, chlorophyll contents, Na+/K+ ratio along with inferior gas exchange attributes and activities of antioxidant enzymes. Moreover, Riogrande was found to be more resistant to salinity stress than Sungold. However, Zn supply significantly alleviated the hazardous effects of salinity by altering compatible solutes accumulation, photosynthetic activity, water relation, soluble sugar contents and providing antioxidant defense against salt stress. The salinity + Zn2 treatment more obviously enhanced RWC (19.0%), MSI (30.8%), SPAD value (17.8%), and activities of SOD (31.7%), POD (28.5%), APX (64.5%) and CAT (23.3%) in Riogrande than Sungold, compared with the corresponding salinity treatment alone. In addition, salinity + Zn2 treatment significantly (P > 0.05) ameliorated salinity stress due to the depreciation in Na+/K+ ratio by 63.3% and 40.8%, Na+ ion relocation from root to shoot by 10.4% and 6.4%, and thereby significantly reduced Na+ ion accumulation by 47.4% and 16.3% in the leaves of Riogrande and Sungold respectively, compared to the salinity treatment alone. Therefore, it was obvious that 30 µM Zn concentration was more effective to induce resistance against salinity stress than 15 µM Zn concentration. Conclusively, it can be reported that exogenous Zn application helps tomato plant to combat adverse saline conditions by modulating photosynthetic and antioxidant capacity along with reduced Na+ uptake at the root surface of tomato plant.

Role of Promising Secondary Metabolites to Confer Resistance Against Environmental Stresses in Crop Plants: Current Scenario and Future Perspectives.

Plants often face incompatible growing environments like drought, salinity, cold, frost, and elevated temperatures that affect plant growth and development leading to low yield and, in worse circumstances, plant death. The arsenal of versatile compounds for plant consumption and structure is called metabolites, which allows them to develop strategies to stop enemies, fight pathogens, replace their competitors and go beyond environmental restraints. These elements are formed under particular abiotic stresses like flooding, heat, drought, cold, etc., and biotic stress such as a pathogenic attack, thus associated with survival strategy of plants. Stress responses of plants are vigorous and include multifaceted crosstalk between different levels of regulation, including regulation of metabolism and expression of genes for morphological and physiological adaptation. To date, many of these compounds and their biosynthetic pathways have been found in the plant kingdom. Metabolites like amino acids, phenolics, hormones, polyamines, compatible solutes, antioxidants, pathogen related proteins (PR proteins), etc. are crucial for growth, stress tolerance, and plant defense. This review focuses on promising metabolites involved in stress tolerance under severe conditions and events signaling the mediation of stress-induced metabolic changes are presented.

TCCA-mediated oxidative rearrangement of tetrahydro-ß-carbolines: facile access to spirooxindoles and the total synthesis of (±)-coerulescine and (±)-horsfiline.

Multi-reactive centered reagents are beneficial in chemical synthesis due to their advantage of minimal material utilization and formation of less by-products. Trichloroisocyanuric acid (TCCA), a reagent with three reactive centers, was employed in the synthesis of spirooxindoles through the oxidative rearrangement of various N-protected tetrahydro-ß-carbolines. In this protocol, low equivalents of TCCA were required to access spirooxindoles (up to 99% yield) with a wide substrate scope. Furthermore, the applicability and robustness of this protocol were proven for the gram-scale total synthesis of natural alkaloids such as (±)-coerulescine (1) and (±)-horsfiline (2) in excellent yields.

Bifunctional thiosquaramide catalyzed asymmetric reduction of dihydro-ß-carbolines and enantioselective synthesis of (-)-coerulescine and (-)-horsfiline by oxidative rearrangement.

Tetrahydro-ß-carboline (THBC) is a tricyclic ring system that can be found in a large number of bioactive alkaloids. Herein, we report a simple and efficient method for the synthesis of enantiopure THBCs through a chiral thiosquaramide (11b) catalyzed imine reduction of dihydro-ß-carbolines (17a-f). The in situ generated Pd-H employed as hydride source in the reaction of differently substituted chiral THBCs (18a-f) afforded high selectivities (R isomers, up to 96% ee) and good isolated yields (up to 88%). Moreover, the chiral thiosquaramide used also afforded exceptional catalyst activity in the syntheses of (-)-coerulescine (5) and (-)-horsfiline (6) with excellent enantioselectivities up to 98% and 93% ee, respectively, via an enantioselective oxidative rearrangement approach.