Visible-Light-Mediated Annulation/Thiolation of 2-Isocyanobiaryls with Disulfides to Organoylthiophenanthridines Derivatives

A visible-light-induced annulation/thiolation of 2-isocyanobiaryls with dialkyl(aryl)disulfides has been established, delivering a sustainable and atom-economic route to 6-organoylthiophenanthridines with wild functional group tolerance and good to excellent yields under oxidant-, base-, and transition-metal-free conditions.

Efficient extraction and purification of benzo[c]phenanthridine alkaloids from Macleaya cordata (Willd) R. Br. by combination of ultrahigh pressure extraction and pH-zone-refining counter-current chromatography with anti-breast cancer activity in vitro

INTRODUCTION

Macleaya cordata (Willd) R. Br. (Papaveraceae family) is a well-known traditional Chinese medicine used to treat muscle pain, inflamed wounds, and bee bites. Benzo[c]phenanthridine alkaloids are the main active ingredients in M. cordata. In this work, sanguinarine and chelerythrine were efficiently extracted and purified by ultrahigh-pressure extraction (UHPE) technique and pH-zone-refining counter-current chromatography (PZRCCC) from M. cordata.

OBJECTIVE

To develop an efficient UHPE method followed by an efficient separation technique using PZRCCC for benzo[c]phenanthridine alkaloids from the study plant species, and to evaluate the study samples for anti-breast cancer activity.

METHODOLOGY

The optimal extraction conditions were optimised as extraction pressure 200 MPa, extraction solvent 95% ethanol, solid-liquid ratio 1:30 (g/mL) and extraction time 2 min. A two-phase n-hexane/ethyl acetate/i-propanol/water (1:3:1.5:4.5, v/v) solvent system was optimised with 10 mmol triethylamine in the upper phase and 10 mmol trifluoroacetic acid in lower phase in PZRCCC. The sample loading was optimised as 2.50 g. Moreover, the samples were evaluated for anti-breast cancer activity later on.

RESULTS

The 2.50 g sample loading yielded 0.45 g of sanguinarine and 0.59 g chelerythrine in one-step separation using PZRCCC. The anti-breast cancer activities of sanguinarine and chelerythrine were found stronger than positive control (vincristine 5.04 μg/mL) with half-maximal inhibitory concentration values of 0.96 and 3.00 μg/mL, respectively.

CONCLUSION

This study showed that the established methods were efficient in extraction (UHPE) and separation (PZRCCC) of the sanguinarine and chelerythrine from M. cordata.

Construction of indazolo[3,2-a]isoquinolines via [3 + 2] cycloaddition of benzynes

A [3 + 2] annulation protocol for the construction of N-substituted indazolo[3,2-a]isoquinolines starting from benzynes and C,N-cyclic azomethine imines was developed. A diverse range of highly functionalized products indazolo[3,2-a]isoquinolines featuring an indazole scaffold can be easily accessed via a one-step reaction under mild conditions, and they show good anti-proliferative activity on cancer cells.

Synthesis, Bacteriostatic and Anticancer Activity of Novel Phenanthridines Structurally Similar to Benzo[c]phenanthridine Alkaloids

In this study, we report the synthesis, antibacterial and anticancer evaluation of 38 novel phenanthridines that were designed as analogs of the benzo[c]phenanthridine alkaloids. The prepared phenanthridines differ from the benzo[c]phenanthridines in the absence of a benzene A-ring. All novel compounds were prepared from 6-bromo-2-hydroxy-3-methoxybenzaldehyde in several synthetic steps through reduction of Schiff bases and accomplished by radical cyclization. Twelve derivatives showed high antibacterial activity against Bacillussubtilis, Micrococcusluteus and/or Mycobacteriumvaccae at single digit micromolar concentrations. Some compounds also displayed cytotoxicity against the K-562 and MCF-7 cancer cell lines at as low as single digit micromolar concentrations and were more potent than chelerythrine and sanguinarine. The active compounds caused cell-cycle arrest in cancer cells, increased levels of p53 protein and caused apoptosis-specific fragmentation of PARP-1. Biological activity was connected especially with the presence of the N-methyl quaternary nitrogen and 7-benzyloxy substitution (compounds 7i, 7j, 7k, and 7l) of phenanthridine.

Visible light photoredox catalyzed semisynthesis of the analogues of maclekarpine E: a series of 6-vinyl substituted dihydrobenzophenanthridine alkaloids

A photoredox neutral vinylation of dihydrobenzophenanthridines 5 was developed to access the analogue of maclekarpine E (8). In this reaction, Ir(ppy)₂(dtbbpy)PF₆ was used as a photocatalyst (PC) and α-amino C-radicals 6 were the key reactive intermediates.

Cytotoxic activity, apoptosis induction and structure-activity relationship of 8-OR-2-aryl-3,4-dihydroisoquinolin-2-ium salts as promising anticancer agents

As our continuing research, a series of 2-aryl-8-OR-3,4-dihydroisoquinolin-2-ium bromides were evaluated for cytotoxic activity on cancer cells and apoptosis induction in the present study. SAR was derived also. Among them, 23 compounds showed the higher cytotoxicity on MKN-45 cells with IC₅₀ values of 1.99-11.3μM than a standard anticancer drug cis-platinum (IC₅₀=11.4μM) or their natural model compound chelerythrine (IC₅₀=12.7μM); 16 compounds possessed the medium to high activity on NB4 cells with IC₅₀ values of 1.67-4.62μM. SAR analysis showed that both substitution patterns of the N-aromatic ring and the type of 8-OR significantly impact the activity. AO/EB staining and flow cytometry analysis with Annexin V/PI double staining showed that the compounds were able to induce apoptosis in a concentration-dependent manner. The results above suggested that the title compounds are a class of promising compounds for the development of new anti-cancer drugs.

Research Progress on Natural Benzophenanthridine Alkaloids and their Pharmacological Functions: A Review

Benzophenanthridine alkaloids belong to the benzyl isoquinoline family of alkaloids, which are mainly found in Papaveraceae and Rutaceae. To date, over 100 compounds have been isolated from natural herbal medicines which display a variety of pharmacological functions. In this paper, we have summarized the work since 1980 and our own research on benzophenanthridine alkaloids in terms of their chemical structures and distribution, biosynthesis, biotransformation and metabolism, spectral characteristics, pharmacological activities and toxicity. This review lays the foundation for further research into benzophenanthridine alkaloids and their potential applications.

A novel C–C radical–radical coupling reaction promoted by visible light: facile synthesis of 6-substituted N-methyl 5,6-dihydrobenzophenanthridine alkaloids

A photoredox mediated radical–radical coupling ofN-methyl 5,6-dihydrobenzophenanthridine alkaloids with α-electron withdrawing group substituted bromoalkane has been developed.

Pseudocyanides of sanguinarine and chelerythrine and their series of structurally simple analogues as new anticancer lead compounds: Cytotoxic activity, structure-activity relationship and apoptosis induction

6-Cyano dihydrosanguinarine (CNS) and 6-cyano dihydrochelerythrine (CNC) are respectively artificial derivatives of sanguinarine and chelerythrine, two anticancer quaternary benzo[c]phenanthridine alkaloids (QBAs) while 1-cyano-2-aryl-1,2,3,4-tetrahydroisoquinolines (CATHIQs) are a class of structurally simple analogues of CNS or CNC. This study investigated the inhibition activity of CNS, CNC and CATHIQs on cancer cells, apoptosis induction as well as their preliminary SAR. The results showed that CNS and 18 out of CATHIQs showed IC50 values of 0.53 and 0.62-2.24μM against NB4 and 1.53 and 2.99-11.17μM against MKN-45 cells, respectively, superior to a standard anticancer drug cis-platinum with IC50 of 2.39 and 11.36μM. CNC showed a higher activity against NB4 cells (IC50=1.85μM) and a moderate activity against MKN-45 cells (IC50=12.72μM). Among all CATHIQs, 2 and 17 gave the highest activity against NB4 cells and MKN-45 cells (IC50=0.62 and 2.99μM), respectively. DAPI staining, AO/EB staining and ultrastructure analysis of cells demonstrated that CATHIQs were able to induce apoptosis of the cells in a concentration-dependent manner. SAR showed that substitution patterns on the N-aromatic ring significantly influenced the activity of CATHIQs. The general trend was that the introduction of electron-withdrawing substituents like halogen atom, nitro, trifluoromethyl led to a significant improvement of the activity, while the presence of electron-donating groups like methyl, methoxyl caused a reduction of the activity. In most cases, the 2' site was the most favorable substitution position for the improvement of the activity. Thus, the present results strongly suggested that QBA-type pseudocyanides may serve as potential alternatives of anticancer QBAs while CATHIQs should be a class of promising lead compounds for the development of new QBA-like-type anticancer drugs. CNS exhibited the highest cytotoxicities with IC50 values of 0.53μM on NB4 cells and 1.53μM on MKN-45 cells.

Reductive metabolism of the sanguinarine iminium bond by rat liver preparations

BACKGROUND

Sanguinarine (SA) is a quaternary benzo[c]phenanthridine alkaloid that is mainly present in the Papaveraceae family. SA has been extensively studied because of its antimicrobial, anti-inflammatory, antitumor, antihypertensive, antiproliferative and antiplatelet activities. Metabolic studies demonstrated that SA bioavailability is apparently low, and the main pathway of SA metabolism is iminium bond reduction resulting in dihydrosanguinarine (DHSA) formation. Nevertheless, the metabolic enzymes involved in SA reduction are still not known in detail. Thus, the aim of this study was to investigate the rat liver microsomes and cytosol-induced SA iminium bond reduction, and to examine the effects of cytosol reductase inhibitors on the reductive activity.

METHODS

DHSA formation was quantified by HPLC. The possible enzymes responsible for DHSA formation were examined using selective individual metabolic enzyme inhibitors.

RESULTS

When SA was incubated with liver microsomes and cytosol in the absence of NAD(P)H, DHSA, the iminium bond reductive metabolite was formed. The reductase activity of the liver microsomes and cytosol was also enhanced significantly in the presence of NADH. The amount of DHSA formed in the liver cytosol was 4.6-fold higher than in the liver microsomes in the presence of NADH. The reductase activity in the liver cytosol was inhibited by the addition of flavin mononucleotide and/or riboflavin. Inhibition studies indicated that menadione, dicoumarol, quercetin and 7-hydroxycoumarin inhibited rat liver cytosol-mediated DHSA formation in the absence of NADH. However, only menadione and quercetin inhibited rat liver cytosol-mediated DHSA formation in the presence of NADH.

CONCLUSIONS

These results suggest that the SA iminium bond reduction proceeds via two routes in the liver cytosol. One route is direct non-enzymatic reduction by NAD(P)H, and the other is enzymatic reduction by possible carbonyl and/or quinone reductases in the liver cytosol.

Benzo[c]phenanthridine alkaloids exhibit strong anti-proliferative activity in malignant melanoma cells regardless of their p53 status

BACKGROUND

Search for new substances with antiproliferative activity towards melanoma cells is important since malignant melanoma is notoriously resistant to conventional chemotherapy. Benzo[c]phenanthridine alkaloids (BAs) are natural products with significant anti-proliferative activities, therefore they are considered as agents promising for cancer therapy.

OBJECTIVES

The effects of five BAs (sanguinarine, chelerythrine, chelidonine, sanguilutine, and chelilutine) on human malignant melanoma cell lines were compared. The study focused on BAs effects on DNA, anti-apoptotic and p53 protein levels; and the involvement of p53 in cellular responses to alkaloids treatment.

METHODS

Melanoma cell lines, two wild types and two with dysfunctional p53 derived from one of them were used. The mechanism of anti-proliferative and pro-apoptotic effects and the effect on DNA was investigated using MTT assay, flow cytometry, Western blot analysis, fluorescence and electron microscopy.

RESULTS

All tested alkaloids exhibit strong anti-proliferative activity. CHL, CHE and SA induced apoptosis, which was probably mediated by decreasing levels of anti-apoptotic proteins (Bcl-xL, Mcl-1, XIAP) and was accompanied by mitochondrial membrane potential decrease as well as caspase-3 and PARP cleavage. Although all alkaloids caused DNA damage, which was demonstrated by induction of H2AX phosphorylation, none of the tested alkaloids stabilised p53 and their toxicity in cells with non-functional p53 was comparable to wild type cells.

CONCLUSION

Despite the profound similarity of BAs molecular structures, it is clear that the mechanism of cell death induction is different for each alkaloid. Our results indicate that BAs could be effective in malignant melanoma treatment, including tumours which have lost wild type p53.

Overproduction of alkaloid phytoalexins in California poppy cells is associated with the co-expression of biosynthetic and stress-protective enzymes

Many plant cells respond to pathogens by the induction of phytoalexin biosynthesis, but the underlying changes of gene expression are often obscured by their close linkage to the complex rearrangements during pathogen defense, especially the hypersensitive cell death. In root-derived cell cultures of Eschscholzia californica, the overproduction of cytotoxic benzophenanthridine alkaloids can be triggered by a minimum of pathogen pressure that does not evoke hypersensitive reactions. Such conditions activate a signal chain that is initiated by a short contact to low concentrations of yeast glycoprotein elicitor and includes a transient acidification of the cytoplasm. In contrast, high elicitor concentrations signal via an increase of jasmonate and trigger hypersensitive cell death, preceded by a drastic decay of translatable mRNAs. The main changes in protein and mRNA patterns caused by either signal path were compared by 2D proteomic separation, MS/MS sequencing and mRNA-in vitro translation. The four proteins showing the highest overexpression were identical between cells that received low or high-elicitor treatment and overlapped with the three proteins most up-regulated by artificial pH shifts. They comprised one biosynthetic enzyme (norcoclaurine:SAM 4' O-methyl-transferase) plus a unique combination of stress-protective proteins: a heat shock protein (hsp 70); a peptidyl-prolyl-cis/trans isomerase (cyclophilin); and a glyceraldehyde-3-phosphate dehydrogenase. It appears that overproduction of the benzophenanthridine phytoalexins requires the up-regulation of a rate-limiting biosynthetic enzyme plus the coordinated expression of a specific set of protective enzymes and thus is managed like an oxidative stress.

Phytochemical and antimicrobial characterization of Macleaya cordata herb

Macleaya cordata (plume poppy) is a source of bioactive compounds, mainly isoquinoline alkaloids which are used in phytopreparations with anti-inflammatory and antimicrobial activities. In this study, the alkaloids sanguinarine, chelerythrine, their dihydro derivatives, protopine and allocryptopine and phenolics, gallic, protocatechuic, p-hydroxybenzoic, m-hydroxybenzoic, gentisic, p-coumaric, caffeic, ferulic and sinapic acids were determined in extracts prepared from M. cordata aerial part, seeds, and seed capsules using HPLC with UV detection and/or LC/MS with electrospray ionization. The highest content of sanguinarine and chelerythrine was found in capsules. Protopine and allocryptopine were major alkaloids in leaves including footstalks. The seed oil contained dihydrosanguinarine, dihydrochelerythrine and twelve fatty acids of which linoleic, oleic, palmitic and stearic acids predominated. In addition, sanguinarine reductase, a key enzyme in sanguinarine/dihydrosanguinarine equilibrium in plants, was found for the first time, in the soluble proteins of leaves. Finally, extracts were tested for antimicrobial activity using the microdilution method on standard reference bacterial strains.

Palladium- and copper-catalyzed solution phase synthesis of a diverse library of isoquinolines

The solution-phase synthesis of a 111 member isoquinoline library is described. The isoquinoline scaffold has been accessed through the palladium- and copper-catalyzed cyclization of iminoalkynes and the palladium-catalyzed iminoannulation of internal alkynes, followed by diversification of hydroxyl functionality where it is present.