Simple isoquinoline and benzylisoquinoline alkaloids as potential antimicrobial, antimalarial, cytotoxic, and anti-HIV agents

Bioactives from medicinal herb against bedaquiline resistant tuberculosis: removing the dark clouds from the horizon

Tuberculosis is a contagious bacterial ailment that primarily affects the lungs and is brought on by the bacterium Mycobacterium tuberculosis (MTB). An antimycobacterial medication called bedaquiline (BQ) is specified to treat multidrug-resistant tuberculosis (MDR-TB). Despite its contemporary use in clinical practice, the mutations (D32 A/G/N/V/P) constrain the potential of BQ by causing transitions in the structural conformation of the atpE subunit-c after binding. In this study, we have taken the benzylisoquinoline alkaloids from thalictrum foliolosum due to its antimicrobial activity reported in prior literature. We used an efficient and optimized structure-based strategy to examine the wild type (WT) and mutated protein upon molecule binding. Our results emphasize the drastic decline in BQ binding affinity of mutant and WT atpE subunit-c complexes compared to thalirugidine (top hit) from thalictrum foliolosum. The decrease in BQ binding free energy is due to electrostatic energy because nearly every atom in a macromolecule harbors a partial charge, and molecules taking part in molecular recognition will interact electrostatically. Similarly, the high potential mean force of thalirugidine than BQ in WT and mutant complexes demonstrated the remarkable ability to eradicate mycobacteria efficiently. Furthermore, the Alamar blue cell viability and ATP determination assay were performed to validate the computational outcomes in search of novel antimycobacterial. Upon closer examination of the ATP determination assay, it became apparent that both BQ and thalirugidine showed similar reductions in ATP levels at their respective MICs, presenting a potential common mechanism of action.

Bioactivity and In Silico Studies of Isoquinoline and Related Alkaloids as Promising Antiviral Agents: An Insight

Viruses are widely recognized as the primary cause of infectious diseases around the world. The ongoing global pandemic due to the emergence of SARS-CoV-2 further added fuel to the fire. The development of therapeutics becomes very difficult as viruses can mutate their genome to become more complex and resistant. Medicinal plants and phytocompounds could be alternative options. Isoquinoline and their related alkaloids are naturally occurring compounds that interfere with multiple pathways including nuclear factor-κB, mitogen-activated protein kinase/extracellular-signal-regulated kinase, and inhibition of Ca2+-mediated fusion. These pathways play a crucial role in viral replication. Thus, the major goal of this study is to comprehend the function of various isoquinoline and related alkaloids in viral infections by examining their potential mechanisms of action, structure-activity relationships (SAR), in silico (particularly for SARS-CoV-2), in vitro and in vivo studies. The current advancements in isoquinoline and related alkaloids as discussed in the present review could facilitate an in-depth understanding of their role in the drug discovery process.

A New Series of Tungstophosphoric Acid-Polymeric Matrix Catalysts: Application in the Green Synthesis of 2-Benzazepines and Analogous Rings

A new series of composite materials (PLMTPA) based on tungstophosphoric acid (TPA) included in a polymeric matrix of polyacrylamide (PLM), with a TPA:PLM ratio of 20/80, 40/60, and 60/40, were synthesized and well characterized by FT-IR, XRD, 31P MAS-NMR, TGA-DSC, and SEM-EDAX. Their acidic and textural properties were determined by potentiometric titration and nitrogen adsorption–desorption isotherms, respectively. Considering 31P MAS-NMR and FT-IR analyses, the main species present in the samples is the [PW12O40]3− anion that, according to XRD results, is highly dispersed in the polymeric matrix or appears as a noncrystalline phase. The thermogravimetric analysis revealed that PLMTPA materials did not undergo any remarkable chemical changes up to 200 °C. Additionally, the PLMTPA materials showed strong acid sites whose number increased with the increment of their TPA content. Finally, PLMTPA materials were used as efficient and recyclable noncorrosive catalysts for the synthesis of 2-benzazepines and related compounds. Good yields (55–88%) and high purity were achieved by a Pictet-Spengler variant reaction between N-aralkylsulfonamides and s-trioxane in soft reaction conditions: low toluene volume, at 70 °C, for 3 h. The described protocol results in a useful and environmentally friendly alternative with operative simplicity. The best catalyst in the optimized reaction conditions, PLMTPA60/40100, was reused six times without appreciable loss of activity.

Microbial transformation of some simple isoquinoline and benzylisoquinoline alkaloids and in vitro studies of their metabolites

Simple isoquinoline alkaloids (heliamine, dehydroheliamine), a phthalide isoquinoline alkaloid noscapine, and an aporphine alkaloid boldine are biosynthetically derived from an amino acid tyrosine. These substrates and a simple synthetic isoquinoline alkaloid (2-acetyl-7-amino-1,2,3,4-tetrahydroisoquinoline) contain an isoquinoline nucleus. The biotransformation of these substrates via reduction, oxidation, hydroxylation, and N-oxidation reactions with different microorganism produced nine metabolites, namely: N-(2-acetyl-1,2,3,4-tetrahydroisoquinolin-7-yl) acetamide (Metabolite 1), heliamine N-oxide (Metabolite 2), 6,7-dimethoxyisoquinoline (Metabolite 3), 3,4-dihydro-6,7-dimethoxy isoquinolin-1-one (Metabolite 4), heliamine (Metabolite 5), dehydroheliamine N-oxide (Metabolite 6), cotarnine (Metabolite 7), 5-hydroxy cotarnine (Metabolite 8), and boldine N-oxide (Metabolite 9). Primarily, the metabolites are structurally elucidated by one-dimensional (1D) and two-dimensional (2D) nuclear magnetic resonance (NMR) analyses, and high-resolution electrospray ionization mass spectrometry (HR-ESIMS). Furthermore, the substrates and their isolated metabolites are evaluated in vitro for their anti-inflammatory, antimicrobial, cytotoxicity, and anticancer activities. The in vitro studies reveal that some of the isolated compounds are potential as anti-inflammatory, antitumor, and antimicrobial leads.

In Silico Study of the Active Compounds of Lindera aggregata (Sims) Kosterm as Anti-coronavirus

Background:

CoVID-19, caused by a new type of coronavirus named SARS-CoV-2, has become a pandemic. Together with SARS-CoV and MERS-CoV, CoVID-19 is a large global outbreak of coronavirus infection; however, its rate of spread is much higher. Since the vaccines and anti-SARS-CoV-2 have not been found, a faster control mechanism is much needed. Traditional herbs have shown the potential for this purpose, as has been demonstrated by the Chinese Government with a high success rate. One of the herbs used was Lindera aggregata, which is part of the collection in Purwodadi Botanic Gardens.

Objectives:

Through in silico study, this research aims to reveal the secondary metabolites contained in L. aggregata that have the potential to serve as anti-SARS-CoV-2 medication as well as showcase their inhibitory mechanisms.

Methods:

The research was conducted through molecular docking analysis of terpenoids and alkaloids contained in the root of L. aggregata, with target proteins 3CLpro, PLpro, Spike, and ACE 2 playing a role in SARS-CoV-2 infection.

Result:

All analyzed compounds tended to interact with all four target proteins with different binding affinity values, but the interaction seemed stronger with 3CLpro and Spike. Terpenoids, linderane and linderalactone had the strongest interaction tendency with 3CLpro, PLpro, and Spike; the compound norboldine, an alkaloid, had the strongest interaction with ACE 2, with a binding affinity value of -8.2 kcal/mol.

Conclusion:

Terpenoids and alkaloids contained in the root of L. aggregata, which caused inhibition of adsorption and replication of SARS-CoV-2, could serve as anti-SARS-CoV-2.

A simple and efficient metal free, additive, or base free dehydrogenation of tetrahydroisoquinolines using oxygen as a clean oxidant

Metal free dehydrogenation of various substituted tetrahydroisoquinolines via a simple and convenient metal free, atom economical route for the synthesis of corresponding isoquinolines under oxygen atmosphere in N-methyl-2-pyrollidone (NMP) is described. Metal free dehydrogenation was carried out without the use of additive or base. A scope of the methodology was demonstrated for a number of aryl and heteroaryl substitutions present at C1 position and ester moiety at C3 position and was found to be good substrates. Substituted isoquinolines (3a–3h) and their esters (3i–3m) were synthesized in very good to excellent yields.

Citronamine A, an Antiplasmodial Isoquinoline Alkaloid from the Australian Marine Sponge Citronia astra

Citronamine A (1), an isoquinoline alkaloid containing an unprecedented pentacyclic ring system, was isolated from the Australian marine sponge Citronia astra. Based on the combination of MS and NMR analyses and comparison of experimental and TDDFT calculated ECD spectra, the absolute structure of 1 was determined. Compound 1 displayed moderate activity against drug sensitive (3D7) and drug resistant (Dd2) strains of the parasite, Plasmodium falciparum, responsible for malaria.

The scaffold-forming steps of plant alkaloid biosynthesis

Alkaloids from plants are characterised by structural diversity and bioactivity, and maintain a privileged position in both modern and traditional medicines. In recent years, there have been significant advances in elucidating the biosynthetic origins of plant alkaloids. In this review, I will describe the progress made in determining the metabolic origins of the so-called true alkaloids, specialised metabolites derived from amino acids containing a nitrogen heterocycle. By identifying key biosynthetic steps that feature in the majority of pathways, I highlight the key roles played by modifications to primary metabolism, iminium reactivity and spontaneous reactions in the molecular and evolutionary origins of these pathways.

The Biological Activity of Natural Alkaloids against Herbivores, Cancerous Cells and Pathogens

The growing incidence of microorganisms that resist antimicrobials is a constant concern for the scientific community, while the development of new antimicrobials from new chemical entities has become more and more expensive, time-consuming, and exacerbated by emerging drug-resistant strains. In this regard, many scientists are conducting research on plants aiming to discover possible antimicrobial compounds. The secondary metabolites contained in plants are a source of chemical entities having pharmacological activities and intended to be used for the treatment of different diseases. These chemical entities have the potential to be used as an effective antioxidant, antimutagenic, anticarcinogenic and antimicrobial agents. Among these pharmacologically active entities are the alkaloids which are classified into a number of classes, including pyrrolizidines, pyrrolidines, quinolizidines, indoles, tropanes, piperidines, purines, imidazoles, and isoquinolines. Alkaloids that have antioxidant properties are capable of preventing a variety of degenerative diseases through capturing free radicals, or through binding to catalysts involved indifferent oxidation processes occurring within the human body. Furthermore, these entities are capable of inhibiting the activity of bacteria, fungi, protozoan and etc. The unique properties of these secondary metabolites are the main reason for their utilization by the pharmaceutical companies for the treatment of different diseases. Generally, these alkaloids are extracted from plants, animals and fungi. Penicillin is the most famous natural drug discovery deriving from fungus. Similarly, marines have been used as a source for thousands of bioactive marine natural products. In this review, we cover the medical use of natural alkaloids isolated from a variety of plants and utilized by humans as antibacterial, antiviral, antifungal and anticancer agents. An example for such alkaloids is berberine, an isoquinoline alkaloid, found in roots and stem-bark of Berberis asculin P. Renault plant and used to kill a variety of microorganisms.

Copper-Catalyzed Benign and Efficient Oxidation of Tetrahydroisoquinolines and Dihydroisoquinolines Using Air as a Clean Oxidant

A green chemical method for mild oxidation of 1,2,3,4-tetrahydroisoquinolines (THIQs) and 3,4-dihydroisoquinolines (DHIQs) has been developed using air (O₂) as a clean oxidant. DHIQs and THIQs could be efficiently oxidized to isoquinolines in dimethyl sulfoxide at 25 °C under an open air atmosphere with CuBr₂ (20 mol %) as the catalyst; different bases [NaOEt and/or 1,8-diazabicyclo[5,4,0]undec-7-ene] were used for the reaction according to the patterns of substituents (R¹, R²).

Oxoisoaporphine Alkaloids: Prospective Anti-Alzheimer's Disease, Anticancer, and Antidepressant Agents

Oxoisoaporphine alkaloids are a family of oxoisoquinoline-derived alkaloids that were first isolated from the rhizome of Menispermum dauricum DC. (Menispermaceae). It has been demonstrated that oxoisoaporphine alkaloids possess various biological properties, such as cholinesterase and β-amyloid inhibition, acting as a topoisomerase intercalator, monoamine oxidase A inhibition, and are expected to become anti-Alzheimer's disease, anticancer, and antidepressant drugs. This review provides an overview of natural sources, synthetic routes, bioactivities, structure-function relationship, and modification investigations into oxoisoaporphine alkaloids, with the aim of providing references to the structure-activity relationships for the design and development of oxoisoaporphine derivatives with higher efficacy and therapeutic potential.

Synthesis of novel (benzimidazolyl)isoquinolinols and evaluation as adenosine A1 receptor tools

G protein-coupled receptors (GPCRs) constitute the largest family of transmembrane receptors in eukaryotes. The adenosine A₁ receptor (A₁AR) is a class A GPCR that is of interest as a therapeutic target particularly in the treatment of cardiovascular disease and neuropathic pain. Increased knowledge of the role A₁AR plays in mediating these pathophysiological processes will help realise the therapeutic potential of this receptor. There is a lack of enabling tools such as selective fluorescent probes to study A₁AR, therefore we designed a series of (benzimidazolyl)isoquinolinols conjugated to a fluorescent dye (31–35, 42–43). An improved procedure for the synthesis of isoquinolinols from tetrahydroisoquinolinols via oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and atmospheric oxygen is reported. This synthetic method offers advantages over previous metal-based methods for the preparation of isoquinolinols and isoquinolines, which are important scaffolds found in many biologically active compounds and natural products. We report the first synthesis of the (benzimidazolyl)isoquinolinol compound class, however the fluorescent conjugates were not successful as A₁AR fluorescent ligands.

Mild, metal free aromatization of tetrahydroisoquinolinols. Synthesis of (benzimidazolyl)isoquinolinols.

Green Routes for the Production of Enantiopure Benzylisoquinoline Alkaloids

Benzylisoquinoline alkaloids (BIAs) are among the most important plant secondary metabolites, in that they include a number of biologically active substances widely employed as pharmaceuticals. Isolation of BIAs from their natural sources is an expensive and time-consuming procedure as they accumulate in very low levels in plant. Moreover, total synthesis is challenging due to the presence of stereogenic centers. In view of these considerations, green and scalable methods for BIA synthesis using fully enzymatic approaches are getting more and more attention. The aim of this paper is to review fully enzymatic strategies for producing the benzylisoquinoline central precursor, (S)-norcoclaurine and its derivatives. Specifically, we will detail the current status of synthesis of BIAs in microbial hosts as well as using isolated and recombinant enzymes.

Identification and characterization of antibacterial compound(s) of cockroaches (Periplaneta americana)

Infectious diseases remain a significant threat to human health, contributing to more than 17 million deaths, annually. With the worsening trends of drug resistance, there is a need for newer and more powerful antimicrobial agents. We hypothesized that animals living in polluted environments are potential sources of antimicrobials. Under polluted milieus, organisms such as cockroaches encounter different types of microbes, including superbugs. Such creatures survive the onslaught of superbugs and are able to ward off disease by producing antimicrobial substances. Here, we characterized antibacterial properties in extracts of various body organs of cockroaches (Periplaneta americana) and showed potent antibacterial activity in crude brain extract against methicillin-resistant Staphylococcus aureus and neuropathogenic Escherichia coli K1. The size-exclusion spin columns revealed that the active compound(s) are less than 10 kDa in molecular mass. Using cytotoxicity assays, it was observed that pre-treatment of bacteria with lysates inhibited bacteria-mediated host cell cytotoxicity. Using spectra obtained with LC-MS on Agilent 1290 infinity liquid chromatograph, coupled with an Agilent 6460 triple quadruple mass spectrometer, tissues lysates were analysed. Among hundreds of compounds, only a few homologous compounds were identified that contained the isoquinoline group, chromene derivatives, thiazine groups, imidazoles, pyrrole-containing analogs, sulfonamides, furanones, and flavanones and known to possess broad-spectrum antimicrobial properties and anti-inflammatory, anti-tumour, and analgesic properties. Further identification, characterization, and functional studies using individual compounds can act as a breakthrough in developing novel therapeutics against various pathogens including superbugs.

Novel Benzo[a]quinolizidine Analogs Induce Cancer Cell Death through Paraptosis and Apoptosis

Paraptosis is nonapoptotic cell death characterized by massive endoplasmic reticulum (ER)- or mitochondria-derived vacuoles. Induction of paraptosis offers significant advantages for the treatment of chemotherapy-resistant tumors compared with anticancer drugs that rely on apoptosis. Because some natural alkaloids induce paraptotic cell death, a novel series of benzo[a]quinolizidine derivatives were synthesized, and their antiproliferative activity and ability to induce cytoplasmic vacuolation were analyzed. Structural optimization led to the identification of the potent compound 22b, which inhibited cancer cell proliferation in vitro and in vivo and profoundly facilitated paraptosis-like cell death and induced caspase-dependent apoptosis. Further investigation revealed that 22b-mediated vacuolation originated from persistent ER stress and upregulation of LC3B. Paraptosis induced by benzo[a]quinolizidine derivatives thus represents an alternative strategy for cancer chemotherapy.

Novel synthesis and reactions of pyrazolyl-substituted tetrahydrothieno[2,3-c]isoquinoline derivatives

Treatment of isoquinolinecarboxamide 4a with triethyl orthoformate, chloroacetyl chloride or carbon disulfide afforded the pyrimidinone 7, oxopyrimidinethione 12 and chloromethylpyrimidinone 18, respectively. These products were used as versatile starting materials for synthesis of other heterocyclic compounds. The heterocyclic hydrazide 6 was also obtained.

A facile palladium catalysed 3-component cascade route to functionalised isoquinolinones and isoquinolines

We present a novel and facile route to functionalised isoquinolinones and isoquinolines in good yields.

A metal-free cyclic iminium induced one-pot double annulation cascade: access to dihydroisoquinolinium (DHIQ) salts

A reactive cyclic iminium induced one-pot Groebke–Blackburn–Bienayme (GBB) double annulation cascade (DAC) for the synthesis of skeletally diverse DHIQ salts has been described. The key features of this protocol are solvent-free, robust method, clean reaction profile and operational simplicity.

Enantioselective Oxidative Aerobic Dealkylation of N-Ethyl Benzylisoquinolines by Employing the Berberine Bridge Enzyme

N-Dealkylation methods are well described for organic chemistry and the reaction is known in nature and drug metabolism; however, to our knowledge, enantioselective N-dealkylation has not been yet reported. In this study, exclusively the (S)-enantiomers of racemic N-ethyl tertiary amines (1-benzyl-N-ethyl-1,2,3,4-tetrahydroisoquinolines) were dealkylated to give the corresponding secondary (S)-amines in an enantioselective fashion at the expense of molecular oxygen. The reaction is catalyzed by the berberine bridge enzyme, which is known for CC bond formation. The dealkylation was demonstrated on a 100 mg scale and gave optically pure dealkylated products (ee>99 %).

An expedient approach to 1,2-dihydroisoquinoline derivatives via cobalt catalysed 6-endo dig cyclization followed by Mannich condensation of o-alkynylarylaldimines

A highly effective 6-endo dig cyclisation of o-alkynylaldimines to 1,2-dihydroisoquinolines has been described via direct and nitro Mannich condensation using inexpensive and readily available cobalt chloride as catalyst. This strategy provides an effective procedure for the synthesis of substituted 1,2-dihydroisoquinolines derivatives in moderate to high yields. An addition of pronucleophiles, such as nitromethane, acetone and α-hydroxyacetone, to o-alkynylarylaldimines has been achieved via isoquinolinium intermediate.

Alkaloids: an overview of their antibacterial, antibiotic-enhancing and antivirulence activities

With reports of pandrug-resistant bacteria causing untreatable infections, the need for new antibacterial therapies is more pressing than ever. Alkaloids are a large and structurally diverse group of compounds that have served as scaffolds for important antibacterial drugs such as metronidazole and the quinolones. In this review, we highlight other alkaloids with development potential. Natural, semisynthetic and synthetic alkaloids of all classes are considered, looking first at those with direct antibacterial activity and those with antibiotic-enhancing activity. Potent examples include CJ-13,136, a novel actinomycete-derived quinolone alkaloid with a minimum inhibitory concentration of 0.1 ng/mL against Helicobacter pylori, and squalamine, a polyamine alkaloid from the dogfish shark that renders Gram-negative pathogens 16- to >32-fold more susceptible to ciprofloxacin. Where available, information on toxicity, structure-activity relationships, mechanisms of action and in vivo activity is presented. The effects of alkaloids on virulence gene regulatory systems such as quorum sensing and virulence factors such as sortases, adhesins and secretion systems are also described. The synthetic isoquinoline alkaloid virstatin, for example, inhibits the transcriptional regulator ToxT in Vibrio cholerae, preventing expression of cholera toxin and fimbriae and conferring in vivo protection against intestinal colonisation. The review concludes with implications and limitations of the described research and directions for future research.

Exploration of aziridine- and β-lactam-based hybrids as both bioactive substances and synthetic intermediates in medicinal chemistry

The concept of pharmacophore hybridization is attracting an increasing interest from medicinal chemists. Whereas the main motivation for the application of this methodology relates to the pharmacological advantages associated with hybrid molecules, molecular hybridization can also deliver a synthetic advantage through selective chemical modification of the more reactive entity within hybrid systems. Moreover, if both features are combined, new hybrid structures result displaying both a biological and a synthetic benefit, and elaboration of this methodology might culminate in structural diversity and chemical novelty. In this perspective, a new approach based on hybrid structures combining a biologically interesting yet rather chemically reactive nucleus with a privileged heterocyclic scaffold is discussed by means of β-lactam-purine chimeras useful in antiviral research and aziridine-(iso)quinoline hybrids for antimalarial purposes.