A mild synthetic route to α-nitroso diaryl pyrroles

A new synthetic method to access α-nitroso pyrroles is presented. This method utilises the nitrosonium salt NOBF4, enabling short reaction times (<10 minutes) and avoiding the harsh acidic conditions usually associated with pyrrole nitrosation. Application of this procedure to diarylated pyrroles yielded several novel nitroso-pyrroles. Modifications to the method, through exclusion of air and inclusion of a mild base, allowed for the nitrosation of pyrroles bearing aryl groups substituted with electron-donating groups. Attempts to nitrosylate pyrroles bearing alkyl substituents resulted in the formation of a dimeric material composed of a pyrrolic unit and a 2-hydroxyimino-protected 1,5-dihydro-2H-pyrrol-2-one.

A Review of the Chemistry and Biological Activities of Natural Colorants, Dyes, and Pigments: Challenges, and Opportunities for Food, Cosmetics, and Pharmaceutical Application

Natural pigments are important sources for the screening of bioactive lead compounds. This article reviewed the chemistry and therapeutic potentials of over 570 colored molecules from plants, fungi, bacteria, insects, algae, and marine sources. Moreover, related biological activities, advanced extraction, and identification approaches were reviewed. A variety of biological activities, including cytotoxicity against cancer cells, antioxidant, anti-inflammatory, wound healing, anti-microbial, antiviral, and anti-protozoal activities, have been reported for different pigments. Considering their structural backbone, they were classified as naphthoquinones, carotenoids, flavonoids, xanthones, anthocyanins, benzotropolones, alkaloids, terpenoids, isoprenoids, and non-isoprenoids. Alkaloid pigments were mostly isolated from bacteria and marine sources, while flavonoids were mostly found in plants and mushrooms. Colored quinones and xanthones were mostly extracted from plants and fungi, while colored polyketides and terpenoids are often found in marine sources and fungi. Carotenoids are mostly distributed among bacteria, followed by fungi and plants. The pigments isolated from insects have different structures, but among them, carotenoids and quinone/xanthone are the most important. Considering good manufacturing practices, the current permitted natural colorants are: Carotenoids (canthaxanthin, β-carotene, β-apo-8'-carotenal, annatto, astaxanthin) and their sources, lycopene, anthocyanins, betanin, chlorophyllins, spirulina extract, carmine and cochineal extract, henna, riboflavin, pyrogallol, logwood extract, guaiazulene, turmeric, and soy leghemoglobin.

Prodigiosin as an antibiofilm agent against multidrug-resistant Staphylococcus aureus

Staphylococcus aureus is known for forming bacterial biofilms that confer increased antimicrobial resistance. Combining antibiotics with antibiofilm agents is an alternative approach, but the antibiofilm ability of prodigiosin (PG), a potential antibiotic synergist, against antimicrobial-resistant (AMR) S. aureus remains to be understood. The antibiofilm activity of PG against 29 clinical AMR S. aureus strains was evaluated using crystal violet staining, and its synergistic effects with vancomycin (VAN) was confirmed using the checkerboard test. The viability and metabolic activity of biofilms and planktonic cells were also assessed. The results revealed that PG exhibited promising inhibitory activity against biofilm formation and synergistic activity with VAN. It effectively reduced the metabolic activity of biofilms and suppressed the production of exopolysaccharides, which might be attributed to the downregulation of biofilm-related genes such as sarA, agrA, and icaA. These findings suggest that PG could be used as a preventive coating or adjuvant against biofilms in clinical settings.

Mechanisms underlying the inhibitory effects of Cd2+ on prodigiosin synthesis in Serratia marcescens KMR-3

Prodigiosin (2-methyl-3-pentyl-6-methoxyprodiginine), a red-colored microbial pigment, is produced in large quantities by Serratia marcescens KMR-3. This bacterium can grow in a medium with a Cd²⁺ concentration of 500 mg/L, but it does not produce prodigiosin when the Cd²⁺ concentration in the medium is higher than 140 mg/L. Therefore, we investigated the mechanisms by which Cd²⁺ inhibits prodigiosin synthesis. Upon addition of Cd²⁺ to the medium, the expression of the prodigiosin (pig) gene cluster was significantly downregulated. Simultaneously, genes encoding proteins related to the synthesis of arginine and proline(prodigiosin precursors) were significantly downregulated, while the degradation-related genes were upregulated. Furthermore, PigF, which encodes a key enzyme involved in the synthesis of 4-methoxy-2,2'-bipyrrole-5-carboxaldehyde and PigC, which encodes a key enzyme involved in the last step of prodigiosin synthesis, were downregulated by 80% and 55%, respectively, following Cd²⁺ treatment. As PigC and PigF are located on the cell membrane and are involved in the final steps of prodigiosin synthesis, the cell membrane might be presumed to be the site of prodigiosin synthesis. The bacterial membrane exhibited different degrees of elongation, folding, fragmentation, and sagging after the addition of Cd²⁺, while likely destroying the site of prodigiosin synthesis.

Bis(N-picolinamido)cobalt(II) Complexes Display Antifungal Activity toward Candida albicans and Aspergillus fumigatus

This report highlights the synthesis and characterization of ten new bis(N-picolinamido)cobalt(II) complexes of the type [(L)2 CoX2 ]0/2+ , whereby L=N-picolinamide ligand and X=diisothiocyanato (-NCS), dichlorido (-Cl) or diaqua (-OH2 ) ligands. Single crystal X-ray (SC-XRD) analysis for nine of the structures are reported and confirm the picolinamide ligand is bound to the Co(II) center through a neutral N,O binding mode. With the addition of powder X-ray diffraction (PXRD), we have confirmed the cis and trans ligand arrangements of each complex. All complexes were screened against several fungal species and show increased antifungal activity. Notably, these complexes had significant activity against strains of Candida albicans and Aspergillus fumigatus, with several compounds exhibiting growth inhibition of >80 %, and onecompound inhibiting Aspergillus fumigatus hyphal growth by >90 %. Conversely, no antifungal activity was exhibited toward Cryptococcus neoformans and no cytotoxicity towards mammalian cell lines.

Synthesis of sulfenyl dipyrroles via reaction of α-free pyrroles with thionyl chloride

Sulfenyl dipyrroles feature two pyrroles linked via a sulfenyl bridge. The synthesis of sulfenyl dipyrroles has typically involved SCl2 as the sulfur source. However, SCl2 is no longer readily available within North America and Europe. Herein we report a new synthesis of sulfenyl dipyrroles using SOCl2 as the sulfur source and reductant. Although five new sulfenyl dipyrroles were synthesized and isolated via this route, functional group tolerance proved limited. A potential mechanism for the reaction, involving reduction of a sulfinyl moiety by SOCl2, is briefly explored.

Production and Potential Applications of Bioconversion of Chitin and Protein-Containing Fishery Byproducts into Prodigiosin: A Review

The technology of microbial conversion provides a potential way to exploit compounds of biotechnological potential. The red pigment prodigiosin (PG) and other PG-like pigments from bacteria, majorly from Serratia marcescens, have been reported as bioactive secondary metabolites that can be used in the broad fields of agriculture, fine chemicals, and pharmacy. Increasing PG productivity by investigating the culture conditions especially the inexpensive carbon and nitrogen (C/N) sources has become an important factor for large-scale production. Investigations into the bioactivities and applications of PG and its related compounds have also been given increased attention. To save production cost, chitin and protein-containing fishery byproducts have recently been investigated as the sole C/N source for the production of PG and chitinolytic/proteolytic enzymes. This strategy provides an environmentally-friendly selection using inexpensive C/N sources to produce a high yield of PG together with chitinolytic and proteolytic enzymes by S. marcescens. The review article will provide effective references for production, bioactivity, and application of S. marcescens PG in various fields such as biocontrol agents and potential pharmaceutical drugs.

The production and bioactivity of prodigiosin: quo vadis?

Prodigiosin (PG), a red tripyrrole pigment, belongs to a member of the prodiginine family and is normally secreted by various sources including Serratia marcescens and other Gram-negative bacteria. The studies of PG have received innovative devotion as a result of reported antimicrobial, larvicidal and anti-nematoid immunomodulation and antitumor properties, owing to its antibiotic and cytotoxic activities. This review provides a comprehensive summary of research undertaken toward the isolation and structural elucidation of the prodiginine family of natural products. Additionally, the current evidence-based understanding of the biological activities and medicinal potential of PG is employed to determine the efficacy, with some reports of information related to pharmacokinetics, pharmacodynamics and toxicology.

Novel Prodiginine Derivatives Demonstrate Bioactivities on Plants, Nematodes, and Fungi

Bacterial metabolites represent an invaluable source of bioactive molecules which can be used as such or serve as chemical frameworks for developing new antimicrobial compounds for various applications including crop protection against pathogens. Prodiginines are tripyrrolic, red-colored compounds produced by many bacterial species. Recently, due to the use of chemical-, bio-, or mutasynthesis, a novel group of prodiginines was generated. In our study, we perform different assays to evaluate the effects of prodigiosin and five derivatives on nematodes and plant pathogenic fungi as well as on plant development. Our results showed that prodigiosin and the derivatives were active against the bacterial feeding nematode Caenorhabditis elegans in a concentration- and derivative-dependent manner while a direct effect on infective juveniles of the plant parasitic nematode Heterodera schachtii was observed for prodigiosin only. All compounds were found to be active against the plant pathogenic fungi Phoma lingam and Sclerotinia sclerotiorum. Efficacy varied depending on compound concentration and chemical structure. We observed that prodigiosin (1), the 12 ring- 9, and hexenol 10 derivatives are neutral or even positive for growth of Arabidopsis thaliana depending on the applied compound concentration, whereas other derivatives appear to be suppressive. Our infection assays revealed that the total number of developed H. schachtii individuals on A. thaliana was decreased to 50% in the presence of compounds 1 or 9. Furthermore, female nematodes and their associated syncytia were smaller in size. Prodiginines seem to indirectly inhibit H. schachtii parasitism of the plant. Further research is needed to elucidate their mode of action. Our results indicate that prodiginines are promising metabolites that have the potential to be developed into novel antinematodal and antifungal agents.

Insights into the anti-infective properties of prodiginines

Prodiginines are a large family of tripyrrole alkaloids that contain natural members produced by various bacteria and non-natural members obtained from chemical synthesis, enzymatic synthesis, and mutasynthesis. These compounds have attracted a great deal of attention due to their wide range of fascinating properties including anti-infective, anticancer, and immunosuppressive activities. In consideration of the great need for novel and effective anti-infective agents, this review is mainly focused on the current status of research on the anti-infective properties of prodiginines, highlighting their antibacterial, antifungal, antiprotozoal, anti-larval, and antiviral activities. Additionally, the multiple mechanisms by which prodiginines exert their anti-infective effects will also be discussed.

A step-wise synthetic approach is necessary to access γ-conjugates of folate: folate-conjugated prodigiosenes

Despite the vast literature that describes reacting folic acid with a pharmacophore, this route is ineffective in providing the correct regioisomer of the resulting conjugate. We herein present a step-wise route to the preparation of nine folate conjugates of the tripyrrolic prodigiosene skeleton. The strict requirement for step-wise construction of the folate core is demonstrated, so as to achieve conjugation at only the desired γ-carboxylic acid and thus maintain the α-carboxylic site for folate receptor (FRα) recognition. Linkages via ethylenediamine, polyethylene glycol and glutathione are demonstrated.

Despite the vast literature that describes reacting folic acid with a pharmacophore, this route is ineffective in providing the correct regioisomer of the resulting conjugate.

PG-Priming Enhances Doxorubicin Influx to Trigger Necrotic and Autophagic Cell Death in Oral Squamous Cell Carcinoma

Synergistic effects between natural compounds and chemotherapy drugs are believed to have fewer side effects with equivalent efficacy. However, the synergistic potential of prodigiosin (PG) with doxorubicin (Dox) chemotherapy is still unknown. This study explores the synergistic mechanism of PG and Dox against oral squamous cell carcinoma (OSCC) cells. Three OSCC cell lines were treated with different PG/Dox combinatory schemes for cytotoxicity tests and were further investigated for cell death characteristics by cell cycle flow cytometry and autophagy/apoptosis marker labelling. When OSCC cells were pretreated with PG, the cytotoxicity of the subsequent Dox-treatment was 30% higher than Dox alone. The cytotoxic efficacy of PG-pretreated was found better than those of PG plus Dox co-treatment and Dox-pretreatment. Increase of Sub-G1 phase and caspase-3/LC-3 levels without poly (ADP-ribose) polymeras (PARP) elevation indicated both autophagy and necrosis occurred in OSCC cells. Dox flux after PG-priming was further evaluated by rhodamine-123 accumulation and Dox transporters analysis to elucidate the PG-priming effect. PG-priming autophagy enhanced Dox accumulation according to the increase of rhodamine-123 accumulation without the alterations of Dox transporters. Additionally, the cause of PG-triggered autophagy was determined by co-treatment with endoplasmic reticulum (ER) stress or AMP-activated protein kinase (AMPK) inhibitor. PG-induced autophagy was not related to nutrient deprivation and ER stress was proved by co-treatment with specific inhibitor. Taken together, PG-priming autophagy could sensitize OSCC cells by promoting Dox influx without regulation of Dox transporter. The PG-priming might be a promising adjuvant approach for the chemotherapy of OSCC.

Decarboxylative arylation of substituted pyrroles N-protected with 2-(trimethylsilyl)ethoxymethyl (SEM)

Palladium-catalyzed decarboxylative arylation is reported using pyrroles N-protected with the 2-(trimethylsilyl)ethoxymethyl (SEM) group and featuring 2-, 3-, and 4-substituents about the pyrrolic framework. In contrast to N-protected pyrroles previously used in decarboxylative arylation, the use of SEM allows deprotection under mild conditions.

An overview of recent advances in duplex DNA recognition by small molecules

As the carrier of genetic information, the DNA double helix interacts with many natural ligands during the cell cycle, and is amenable to such intervention in diseases such as cancer biogenesis. Proteins bind DNA in a site-specific manner, not only distinguishing between the geometry of the major and minor grooves, but also by making close contacts with individual bases within the local helix architecture. Over the last four decades, much research has been reported on the development of small non-natural ligands as therapeutics to either block, or in some cases, mimic a DNA–protein interaction of interest. This review presents the latest findings in the pursuit of novel synthetic DNA binders. This article provides recent coverage of major strategies (such as groove recognition, intercalation and cross-linking) adopted in the duplex DNA recognition by small molecules, with an emphasis on major works of the past few years.

Prodigiosenes conjugated to tamoxifen and estradiol

We report the synthesis of the first click-appended prodigiosene conjugates. Four prodigiosene conjugates of estradiol functionalised at the 7α-position were prepared, as were three prodigiosene conjugates of tamoxifen. The coupling between a prodigiosene and an 11-hydroxy estradiol derivative via an ether linkage was investigated, as was the 11- and 7-functionalisation of the estradiol core. The robustness of estradiol protecting groups was severely challenged by reactions typically used to equip such frameworks for 11- and 7-functionalisation. Specifically, and important to synthesis involving estradiol, TBS, TMS and THP are not useful protecting groups for the functionalisation of this core. When the chemical features of the therapeutic agent limit the choice of protecting group (in this case, prodigiosenes bearing aryl, NH, alkenyl and ester groups), click chemistry becomes an attractive synthetic strategy. The anti-cancer activity of the seven click prodigiosene conjugates was evaluated.

Synthesis and characterization of pyrrolyldipyrrin F-BODIPYs

A series of synthetic analogs of the tripyrrolic natural product prodigiosin were complexed with boron trifluoride to generate the corresponding F-BODIPYs.

Inhibitory Growth of Oral Squamous Cell Carcinoma Cancer via Bacterial Prodigiosin

Chemotherapy drugs for oral cancers always cause side effects and adverse effects. Currently natural sources and herbs are being searched for treated human oral squamous carcinoma cells (OSCC) in an effort to alleviate the causations of agents in oral cancers chemotherapy. This study investigates the effect of prodigiosin (PG), an alkaloid and natural red pigment as a secondary metabolite of Serratia marcescens, to inhibit human oral squamous carcinoma cell growth; thereby, developing a new drug for the treatment of oral cancer. In vitro cultured human OSCC models (OECM1 and SAS cell lines) were used to test the inhibitory growth of PG via cell cytotoxic effects (MTT assay), cell cycle analysis, and Western blotting. PG under various concentrations and time courses were shown to effectively cause cell death and cell-cycle arrest in OECM1 and SAS cells. Additionally, PG induced autophagic cell death in OECM1 and SAS cells by LC3-mediated P62/LC3-I/LC3-II pathway at the in vitro level. These findings elucidate the role of PG, which may target the autophagic cell death pathways as a potential agent in cancer therapeutics.

Natural Compounds from Herbs that can Potentially Execute as Autophagy Inducers for Cancer Therapy

Accumulated evidence indicates that autophagy is a response of cancer cells to various anti-cancer therapies. Autophagy is designated as programmed cell death type II, and is characterized by the formation of autophagic vacuoles in the cytoplasm. Numerous herbs, including Chinese herbs, have been applied to cancer treatments as complementary and alternative medicines, supplements, or nutraceuticals to dampen the side or adverse effects of chemotherapy drugs. Moreover, the tumor suppressive actions of herbs and natural products induced autophagy that may lead to cell senescence, increase apoptosis-independent cell death or complement apoptotic processes. Hereby, the underlying mechanisms of natural autophagy inducers are cautiously reviewed in this article. Additionally, three natural compounds—curcumin, 16-hydroxycleroda-3,13-dien-15,16-olide, and prodigiosin—are presented as candidates for autophagy inducers that can trigger cell death in a supplement or alternative medicine for cancer therapy. Despite recent advancements in therapeutic drugs or agents of natural products in several cancers, it warrants further investigation in preclinical and clinical studies.

Pyrrole N-H Anion Complexes

Synthetic pyrrole-based anion receptors date back to the 1990s. They have been extensively developed in the context of macrocyclic systems as expanded porphyrins and calixpyrroles, and related systems. The chemistry of open-chain pyrrolic systems is, in many respects, no less venerable. It also has more direct analogy to naturally occurring pyrrole-based anion binding motifs. However, it has not been the subject of a comprehensive review. Presented herein is a summary of efforts devoted to the creation of de novo pyrrole-based receptors, as well as the anion recognition chemistry of naturally occurring pyrrolic systems as prodigiosins and their synthetic analogues.

Synthesis and anticancer activity of prodigiosenes bearing C-ring esters and amides

Ten novel prodigiosenes with anticancer activity.

Perenosins: a new class of anion transporter with anti-cancer activity

A new class of anion transporter named ‘perenosins’ consisting of a pyrrole linked through an imine to either an indole, benzimidazole or indazole is reported.

Synthesis and Structure-Activity Relationships of Tambjamines and B-Ring Functionalized Prodiginines as Potent Antimalarials

Synthesis and antimalarial activity of 94 novel bipyrrole tambjamines (TAs) and a library of B-ring functionalized tripyrrole prodiginines (PGs) against a panel of Plasmodium falciparum strains are described. The activity and structure-activity relationships demonstrate that the ring-C of PGs can be replaced by an alkylamine, providing for TAs with retained/enhanced potency. Furthermore, ring-B of PGs/TAs can be substituted with short alkyl substitutions at either 4-position (replacement of OMe) or 3- and 4-positions without impacting potency. Eight representative TAs and two PGs have been evaluated for antimalarial activity against multidrug-resistant P. yoelii in mice in the dose range of 5-100 mg/kg × 4 days by oral administration. The KAR425 TA offered greater efficacy than previously observed for any PG, providing 100% protection to malaria-infected mice until day 28 at doses of 25 and 50 mg/kg × 4 days, and was also curative in this model in a single oral dose (80 mg/kg). This study presents the first account of antimalarial activity in tambjamines.

Synthesis of prodigiosene–estrogen conjugates: optimization of protecting group strategies and anticancer properties

The tripyrrolic prodigiosene skeleton was conjugated to several estrogen ligands. The conjugation was achieved via an ester linker that proved to be unusually sensitive to hydrolysis during synthesis. This work describes the determination of an appropriate protecting group for the hydroxy groups of the estrogen linker. The anticancer properties of the target prodigiosene–estrogen conjugates were evaluated against breast cancer cells and some show selectivity for ER+ breast cancer cell lines.

Prodigiosin alkaloids: recent advancements in total synthesis and their biological potential

The present review article is focused on the medicinal potential and total synthesis of prodigiosins witnessed in the last decade. The aim will be to provide an inspiration to the marvels and pit falls of constructing the polypyrrole heterocycles with in the complex systems.

Stereospecific synthesis of 23-hydroxyundecylprodiginines and analogues and conversion to antimalarial premarineosins via a Rieske oxygenase catalyzed bicyclization

Facile and highly efficient synthetic routes for the synthesis of (S)- and (R)-23-hydroxyundecylprodiginines ((23S)-2, and (23R)-2), 23-ketoundecylprodiginine (3), and deuterium-labeled 23-hydroxyundecylprodiginine ([23-d]-2) have been developed. We demonstrated a novel Rieske oxygenase MarG catalyzed stereoselective bicyclization of (23S)-2 to premarineosin A (4), a key step in the tailoring process of the biosynthesis of marineosins, using a marG heterologous expression system. The synthesis of various A-C-ring functionalized prodiginines 32-41 was achieved to investigate the substrate promiscuity of MarG. The two analogues 32 and 33 exhibit antimalarial and cytotoxic activities stronger than those of the marineosin intermediate 2, against Plasmodium falciparum strains (CQ(S)-D6, CQ(R)-Dd2, and 7G8) and hepatocellular HepG2 cancer cell line, respectively. Feeding of 34-36 to Streptomyces venezuelae expressing marG led to production of novel premarineosins, paving a way for the production of marineosin analogues via a combinatorial synthetic/biosynthetic approach. This study presents the first example of oxidative bicyclization mediated by a Rieske oxygenase.

Influence of B-ring modifications on proton affinity, transmembrane anion transport and anti-cancer properties of synthetic prodigiosenes

We describe how modulating the pK_aof a family of synthetic prodigiosenes, modified on their B-ring, can control the transmembrane transport of anions.