Enantioselective Syntheses of Strychnos and Chelidonium Alkaloids through Regio- and Stereocontrolled Cooperative Catalysis.

We describe enantioselective syntheses of strychnos and chelidonium alkaloids. In the first case, indole acetic acid esters were established as excellent partner nucleophiles for enantioselective cooperative isothiourea/Pd catalyzed α-alkylation. This provides products containing indole-bearing stereocenters in high yield and with excellent levels of enantioinduction in a manner that is notably independent of the N-substituent. This led to concise syntheses of (-)-akuammicine and (-)-strychnine. In the second case, the poor performance of ortho-substituted cinnamyl electrophiles in the enantioselective cooperative isothiourea/Ir catalyzed α-alkylation was overcome by appropriate substituent choice, leading to enantioselective syntheses of (+)-chelidonine, (+)-norchelidonine, and (+)-chelamine.

The synthesis and in vitro biological evaluation of novel fluorinated tetrahydrobenzo[j]phenanthridine-7,12-diones against Mycobacterium tuberculosis.

Tuberculosis (TB) still has a major impact on public health. In order to efficiently eradicate this life-threatening disease, the exploration of novel anti-TB drugs is of paramount importance. As part of our program to design new 2-azaanthraquinones with anti-mycobacterial activity, various "out-of-plane" tetrahydro- and octahydrobenzo[j]phenanthridinediones were synthesized. In this study, the scaffold of the most promising hits was further optimized in an attempt to improve the bioactivity and to decrease enzymatic degradation. The rudiment bio-evaluation of a small library of fluorinated tetrahydrobenzo[j]phenanthridine-7,12-dione derivatives indicated no significant improvement of the bio-activity against intracellular and extracellular Mycobacterium tuberculosis (Mtb). Though, the derivatives showed an acceptable toxicity against J774A.1 macrophages and early signs of genotoxicity were absent. All derivatives showed to be metabolic stabile in the presence of both phase I and phase II murine or human microsomes. Finally, the onset of reactive oxygen species within Mtb after exposure to the derivatives was measured by electron paramagnetic resonance (EPR). Results showed that the most promising fluorinated derivative is still a possible candidate for the subversive inhibition of mycothione reductase.

Synthesis and biological evaluation of 5-aminoethyl benzophenanthridone derivatives as DNA topoisomerase IB inhibitors.

DNA topoisomerase IB (TOP1) regulates DNA topological structure in many cellular metabolic processes and is a validated target for development of antitumor agents. Our previous study revealed that the benzophenanthridone scaffold is a novel chemotype for the discovery of TOP1 inhibitors. In this work, a series of novel 5-aminoethyl substituted benzophenanthridone derivatives have been synthesized and evaluated for TOP1 inhibition and cytotoxicity. Compound 12 exhibits the most potent TOP1 inhibition (+++) and cytotoxicity in human cancer cell lines with GI50 values at nanomolar concentration range. 12 induces the cellular TOP1cc formation and DNA damage, resulting in HCT116 cell apoptosis. The pharmacokinetics, acute toxicity and antitumor efficiency in vivo of 12 were also studied.

Selective inhibition of monoamine oxidase A by chelerythrine, an isoquinoline alkaloid.

Chelerythrine, an isoquinoline alkaloid isolated from the herbaceous perennial Chelidonium majus, was found to potently and selectively inhibit an isoform of recombinant human monoamine oxidase-A (MAO-A) with an IC50 value of 0.55 µM. Chelerythrine was a reversible competitive MAO-A inhibitor (Ki = 0.22 µM) with a potency much greater than toloxatone (IC50 = 1.10 µM), a marketed drug. Other isoquinoline alkaloids tested did not effectively inhibit MAO-A or MAO-B. A structural comparison with corynoline suggested the 1- and/or 2-methoxy groups of chelerythrine increase its inhibitory activity against MAO-A. Molecular docking simulations revealed that the binding affinity of chelerythrine for MAO-A (-9.7 kcal/mol) was greater than that for MAO-B (-4.6 kcal/mol). Docking simulation implied that Cys323 and Tyr444 of MAO-A are key residues for hydrogen-bond interaction with chelerythrine. Our findings suggest chelerythrine is one of the most reversible selective and potent natural inhibitor of MAO-A, and that it be regarded a potential lead compound for the design of novel reversible MAO-A inhibitors.

Specific Cytostatic and Cytotoxic Effect of Dihydrochelerythrine in Glioblastoma Cells: Role of NF-κB/ß-catenin and STAT3/IL-6 Pathways.

BACKGROUND: A glioblastoma is a primary CNS tumor that is more aggressive and lethal than other brain tumors. Its location, rapid proliferation, invasive growth, angiogenesis and immunosuppression are the main factors that limit its treatment, making it a major challenge to neuro-oncology. OBJECTIVE: This study investigated the in vitro effects of the alkaloid dihydrochelerythrine (DHC), which is extracted from Zanthoxylum stelligerum, on the viability, proliferation, cell death and ß-catenin, NFκB, STAT3/pSTAT3 and interleukins roles. METHOD: In vitro experimental models of human (U251 and GL-15) and murine (C6) glioblastoma cells were cultured in the presence of DHC at increasing concentrations for MTT assay and exclusion trypan blue dye to determine EC50. Afterward, C6 and U251 cells were treated with 100 µM DHC or DMSO 0.1% for cell cycle, annexin and expression of ß-catenin/NFκB/STAT3/pSTAT3 by flow cytometry or immunofluorescence. Interleukin quantification was made by Cytometric Bead Array. RESULTS: A significant decrease was observed in C6 and U251 cell viability in a time and dose-dependent manner. GL-15 cell viability decreased only when treated with 200 µM DHC. This maximum concentration affected neither astrocytes nor microglia viability. A cytostatic effect of DHC was observed in C6 and U251 cells after 48 h of 100 µM DHC treatment. After 72 h of DHC treatment, C6 presented 80% of annexin-V+ cells compared to 10% of annexin-V+ U251 cells. C6 cells demonstrated significant high levels of NFκ B and ß-catenin cytoplasmic fraction. Additionally, DHC treatment resulted in higher significant levels of IL-6 than did other interleukins and STAT3 up-regulation in U251 cells. CONCLUSION: These results demonstrate that DHC acts as a chemosensitizing agent selective for glioma cells not affecting non-tumor cells. Considering tumor heterogeneity, DHC demonstrated an anti-cancer potential to activate different cell death pathways. DHC demonstrated could be used for chemotherapy and immunotherapy applications in glioblastomas in the future.

New 2-aryl-7,8-dimethoxy-3,4-dihydroisoquinolin-2-ium salts as potential antifungal agents: synthesis, bioactivity and structure-activity relationships.

The title compounds can be considered as simple analogues of quaternary benzo[c]phenanthridine alkaloids (QBAs). In order to develop potent QBA-like antifungal agents, as our continuing study, a series of new title compounds were synthesized and evaluated for bioactivity against five plant pathogenic fungi by the mycelium growth rate method in this study. The SAR were also derived. The majority of the compounds showed good to excellent inhibition activity with average EC50 values of 7.87-20.0 µM for the fungi, superior to sanguinarine and cherythrine (two QBAs) and the commercial fungicide azoxystrobin. Part of the compounds were more active than commercial fungicides thiabendazole or carbendazim against F. solani, F. graminearum and C. gloeosporioides. Six compounds with average EC50 of 3.5-5.1 µg/mL possessed very great potential for development of new antifungal agents. SAR found that substitution patterns of the two aryl-rings significantly affect the activity. There exists a complex interaction effect between substituents of the two aryl-rings on the activity. Generally, the presence of electron-withdrawing groups on the C-ring can significantly increase the activity. These findings will be of great importance for the design of more potent antifungal isoquinoline agents.

Mild C(sp3)-H functionalization of dihydrosanguinarine and dihydrochelerythrine for development of highly cytotoxic derivatives.

A series of C(6)-substituted dihydrobenzo[c]phenanthridines were synthesized by mild copper-catalyzed C(sp3)-H functionalization of dihydrosanguinarine (2) and dihydrochelerythrine (3) with certain nucleophiles selected to enhance cytotoxicity against human breast, colorectal, and prostate cancer cell lines. We also investigated the cytotoxicity of our previously reported C(6)-functionalized N-methyl-5,6-dihydrobenzo[c]phenanthridines 1a-1e to perform structure-activity relationship (SAR) studies. Among the target compounds, five ß-aminomalonates (1a, 1b, 2a, 2b, and 3b), one α-aminophosphonate (2c), and one nitroalkyl derivative (2h) exhibited half maximal inhibitory concentration (IC50) values in the range of 0.6-8.2 µM. Derivatives 1b, 2b and 2h showed the lowest IC50 values, with 2b being the most potent with values comparable to those of the positive control doxorubicin. On the basis of their IC50 values, derivatives 1a, 1b, 2a, 2b, 2h, and 3b were selected to evaluate the apoptotic PC-3 cell death at 10 µM by flow cytometry using propidium iodide and fluorescein isothiocyanate-conjugated Annexin V dual staining. The results indicated that the cytotoxic activity of the tested compounds in PC-3 cells is due to the induction of apoptosis, with 1a and 2h being the most active (55% of early apoptosis induction). Our preliminary SAR study showed that the incorporation of specific malonic esters, dialkyl phosphites and nitro alkanes on scaffolds 1-3 significantly enhanced their cytotoxic properties. Moreover, it appears that the electron donating 7,8-methylenedioxy group allowed derivatives of 2 to exhibit higher cytotoxicity than derivatives of 1 and 3. The present results suggest that derivatives 2b and 2h may be considered as potential lead compounds for the development of new anticancer agents.

Dihydrochelerythrine and its derivatives: Synthesis and their application as potential G-quadruplex DNA stabilizing agents.

A convenient route was envisaged toward the synthesis of dihydrochelerythrine (DHCHL), 4 by intramolecular Suzuki coupling of 2-bromo-N-(2-bromobenzyl)-naphthalen-1-amine derivative 5 via in situ generated arylborane. This compound was converted to (±)-6-acetonyldihydrochelerythrine (ADC), 3 which was then resolved by chiral prep-HPLC. Efficiency of DHCHL for the stabilization of promoter quadruplex DNA structures and a comparison study with the parent natural alkaloid chelerythrine (CHL), 1 was performed. A thorough investigation was carried out to assess the quadruplex binding affinity by using various biophysical and biochemical studies and the binding mode was explained by using molecular modeling and dynamics studies. Results clearly indicate that DHCHL is a strong G-quadruplex stabilizer with affinity similar to that of the parent alkaloid CHL. Compounds ADC and DHCHL were also screened against different human cancer cell lines. Among the cancer cells, (±)-ADC and its enantiomers showed varied (15-48%) inhibition against human colorectal cell line HCT116 and breast cancer cell line MDA-MB-231 albeit low enantio-specificity in the inhibitory effect; whereas DHCHL showed 30% inhibition against A431 cell line only, suggesting the compounds are indeed cancer tissue specific.

Catalytic Arylsulfonyl Radical Triggered 1,7-Enyne Bicyclizations.

A new metal-free bicyclization reaction of 1,7-enynes anchored by α,ß-conjugates with arylsulfonyl radicals generated in situ from sulfonyl hydrazides has been established using tert-butyl hydroperoxide and tetrabutylammonium iodide. The reactions occurred through sulfonylation/6-exo-dig/6-exo-trig bicyclization/in situ desulfonylation/5-exo-trig cyclization/alkyl or alkenyl migration cascade mechanism to give benzo[j]phenanthridines regioselectively.

New methods for the synthesis of naphthyl amines; application to the synthesis of dihydrosanguinarine, sanguinarine, oxysanguinarine and (±)-maclekarpines B and C.

A new method for preparing naphthyl amines from 1,5 unsaturated dicarbonyl precursors is described; the utility of this new method was proven in the syntheses of several natural products, all containing the benzo[c]phenanthridine core and enabled by a radical promoted cyclisation of the naphthyl amine products formed in the key cyclisation.

Fluorescence properties of selected benzo[c]phenanthridines.

The fluorescence properties of selected benzo[c]phenanthridines (BPs) were examined. The effect of structure, pH and solvent on the fluorescence properties has been investigated. It was found out that the presence of charged iminium nitrogen significantly decreased the fluorescence of the compounds. The fluorescence (intensity as well as emission spectra shape) of the investigated compounds was significantly dependent on pH as well as used solvent. The utilization in epigenetic modification mechanisms studies as demethylase probe and as possible pH indicator was suggested.

Alkyltriflate-triggered annulation of arylisothiocyanates and alkynes leading to multiply substituted quinolines through domino electrophilic activation.

The reaction of arylisothiocyanate, alkyltriflate, and alkynes leads to variously substituted quinolines in high yields. The reaction undergoes alkyltriflate-triggered domino electrophilic activation and avoids the use of a transition-metal catalyst. A variety of functional groups are tolerated in the quinoline ring.

Expeditious approach to pyrrolophenanthridones, phenanthridines, and benzo[c]phenanthridines via organocatalytic direct biaryl-coupling promoted by potassium tert-butoxide.

A methodology involving a "transition metal-free" intramolecular biaryl-coupling of o-halo-N-arylbenzylamines has been developed in the presence of potassium tert-butoxide and an organic molecule as catalyst. The reaction appears to proceed through KO(t)Bu-promoted intramolecular homolytic aromatic substitution (HAS). Interestingly, this biaryl coupling also works in the presence of potassium tert-butoxide as sole promoter. On extending our approach further, we found that N-acyl 2-bromo-N-arylbenzylamines undergo a one-pot N-deprotection/biaryl coupling followed by oxidation, thus offering an expeditious route to the phenanthridine and benzo[c]phenanthridine skeletons. The strategy has been applied to a concise synthesis of Amaryllidaceae alkaloids viz. oxoassoanine (1b), anhydrolycorinone (1d), 5,6-dihydrobicolorine (2d), trispheridine (2b), and benzo[c]phenanthridines alkaloids dihydronitidine (3b), dihydrochelerythidine (3d), dihydroavicine (3f), nornitidine (3h), and norchelerythrine (3j).

Exploration of natural compounds as sources of new bifunctional scaffolds targeting cholinesterases and beta amyloid aggregation: the case of chelerythrine.

The presented project started by screening a library consisting of natural and natural based compounds for their acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory activity. Active compounds were chemically clustered into groups and further tested on the human cholinesterases isoforms. The aim of the presented study was to identify compounds that could be used as leads to target two key mechanisms associated with the AD's pathogenesis simultaneously: cholinergic depletion and beta amyloid (Aß) aggregation. Berberin, palmatine and chelerythrine, chemically clustered in the so-called isoquinoline group, showed promising cholinesterase inhibitory activity and were therefore further investigated. Moreover, the compounds demonstrated moderate to good inhibition of Aß aggregation as well as the ability to disaggregate already preformed Aß aggregates in an experimental set-up using HFIP as promotor of Aß aggregates. Analysis of the kinetic mechanism of the AChE inhibition revealed chelerythrine as a mixed inhibitor. Using molecular docking studies, it was further proven that chelerythrine binds on both the catalytic site and the peripheral anionic site (PAS) of the AChE. In view of this, we went on to investigate its effect on inhibiting Aß aggregation stimulated by AChE. Chelerythrine showed inhibition of fibril formation in the same range as propidium iodide. This approach enabled for the first time to identify a cholinesterase inhibitor of natural origin-chelerythrine-acting on AChE and BChE with a dual ability to inhibit Aß aggregation as well as to disaggregate preformed Aß aggregates. This compound could be an excellent starting point paving the way to develop more successful anti-AD drugs.

Structural modification of sanguinarine and chelerythrine and their in vitro acaricidal activity against Psoroptes cuniculi.

Sanguinarine (1) and chelerythrine (2) are two quaternary benzo[c]phenanthridine alkaloids (QBAs). Eighteen derivatives of 1 and 2 were synthesized by modification of C=N(+) bond and evaluated for their in vitro acaricidal activity against Psoroptes cuniculi, a mange mite. A new method was developed to prepare 6-alkoxy dihydro derivatives of 1 and 2 (1a-e, 2a-e). Among all the compounds, only 6-alkoxy dihydrosanguinarines (1a-e) showed significant acaricidal activity at 5.0 mg/mL and 1a possessed the strongest activity (50% lethal concentrations (LC(50))=339.70±0.75 mg/L, 50% lethal time (LT(50))=6.53±0.04 h), comparable with a standard drug ivermectin (LC(50)=168.19±11.79 mg/L, LT(50)=16.54±0.11 h). The iminium moiety in 1 and 2 was proven to be the determinant for their acaricidal properties. 6-Alkoxy dihydro derivatives (1a-e, 2a-e) were prodrugs of 1 and 2. Compared with 7,8-dimethoxy groups, 7,8-methylenedioxy group was able to significantly improve the bioactivity. The present results suggested that QBAs are promising candidates or lead compounds for the development of new isoquinoline acaricidal agents.

Short synthesis and antimalarial activity of fagaronine.

Herein, we report a new synthesis of fagaronine 1, inspired by the synthesis reported by Luo for nornitidine. The in vitro biological activity of fagaronine against malaria on several chloroquine-sensitive and resistant Plasmodium falciparum strains was confirmed, and the selectivity index compared to mammalian cells was calculated. Fagaronine was found to have very good antimalarial activity in vivo, comparable to the activity of the reference compound chloroquine. Therefore, fagaronine appears to be a good potential lead for the design of new antimalarial molecules.

Total syntheses of chelidonine and norchelidonine via an enamide-benzyne-[2 + 2] cycloaddition cascade.

Total syntheses of chelidonine and norchelidonine featuring an enamide-benzyne-[2 + 2] cycloaddition initiated cascade is described. The cascade includes a pericyclic ring-opening and intramolecular Diels-Alder reaction.

Alkaloids from Chelidonium majus and their inhibitory effects on LPS-induced NO production in RAW264.7 cells.

A new alkaloid, methyl 2'-(7,8-dihydrosanguinarine-8-yl)acetate (1), together with six known alkaloids, stylopine (2), protopine (3), norchelidonine (4), chelidonine (5), berberine (6), and 8-hydroxydihydrosanguinarine (7), were isolated from Chelidonium majus. Their chemical structures were primarily established using 1D and 2D NMR techniques and mass spectrometry. The anti-inflammatory activity of the isolates was examined for their inhibitory effects on LPS-induced NO production in macrophage RAW264.7 cells. Among them, compounds 5 and 7 showed strong inhibitory activities toward the LPS-induced NO production in macrophage RAW264.7 cells with IC(50) values of 7.3 and 4.5 µM, respectively. In addition, compounds 5 and 7 inhibited the inductions of COX-2 and iNOS mRNA in dose-dependent manners, indicating that these compounds attenuated the syntheses of these transcripts at the transcriptional level.

Structural modification of sanguinarine and chelerythrine and their antibacterial activity.

In this study, five derivatives of sanguinarine (1) and chelerythrine (2) were prepared, with 1 and 2 as starting materials, by reduction, oxidation and nucleophilic addition to the iminium bond C=N+. The structures of all compounds were elucidated on account of their MS, ¹H-NMR and ¹³C-NMR data. The antibacterial activities of all compounds were screened, using Staphylococcus aureus, Escherichia coli, Aeromonas hydrophila and Pasteurella multocida as test bacteria. The minimum bacteriostatic concentration and minimum bactericidal concentration of the active compounds were determined by the turbidity method. The structure-activity relationships of 1 and 2 were discussed. The results showed that 1, 2 and their pseudoalcoholates were found to be potent inhibitors to S. aureus, E. coli and A. hydrophila, while the other derivatives were found to be inactive. The pseudoalcoholates might be the prodrugs of 1 and 2. The iminium bond in the molecules of 1 or 2 was the determinant for antibacterial activity, and the substituents at the 7 and 8 positions influenced the antibacterial activities of 1 and 2 against different bacteria.