Synthesis and evaluation of aplysinopsin analogs as inhibitors of human monoamine oxidase A and B

Marine indole alkaloid diversity and bioactivity. What do we know and what are we missing?

Covering: marine indole alkaloids (n = 2048) and their reported bioactivities up to the end of 2021Despite increasing numbers of marine natural products (MNPs) reported each year, most have only been examined for cytotoxic, antibacterial, and/or antifungal biological activities with the majority found to be inactive in these assays. In this context, why are natural products continuing to be examined in assays they are unlikely to show significant activity in, and what targets might be more useful for expanding knowledge of their biologically relevant chemical space? We have undertaken a meta-analysis of the biological activities for 2048 marine indole alkaloids (MIAs), a diverse sub-class of MNPs reported up to the end of 2021, and this has highlighted that the bioactivity potentials for up to 86% of published MIAs remains underexplored and/or undefined. Although most published MIAs are not cytotoxic or antimicrobial, there is a continued focus on using these assays to evaluate new structurally related analogues. Using cheminformatics analyses, the chemical diversity of the 2048 MIAs were clustered using fragment based fingerprints and their reported bioactivity potency towards specific disease targets was assessed for structure activity trends. These analyses showed that there are groups of MIAs that possess potent and diverse activities and that many analogues, previously tested only in cellular toxicity assays, could be better exploited to generate structure activity relationships associated with leads to treat emerging diseases. A collection of indole drug and drug-lead structures from non-natural sources were also incorporated into the dataset providing complementary bioactivity profiles that were further used to predict underexplored areas of potential new activity and to better direct future testing of MIAs. Our findings clearly suggest the biological evaluation of MIAs continues to be conducted on a narrow range of bioassays and disease targets, and that shifting the focus to non-toxic disease targets should provide expanded knowledge of biologically relevant chemical space aimed at maximising the potential of MIAs for drug discovery.

Synthetic Analogs of Marine Alkaloid Aplysinopsin Suppress Anti-Apoptotic Protein BCL2 in Prostate Cancer

Aplysinopsins are a class of indole alkaloids that possess various pharmacological activities. Although their action has been studied in regard to many diseases, their effect on prostate cancer has not yet been examined. Therefore, we synthesized a new series of aplysinopsin analogs and investigated their cytotoxic activity against prostate cancer. Five analogs showed high antitumor activity via suppressing the expression of the anti-apoptotic gene Bcl2, simulationously increasing the expression of the pro-apoptotic genes p53, Bax and Caspase 3. The inhibition of BCL2 led to the activation of BAX, which in turn activated Caspase 3, leading to apoptosis. This dual mechanism of action via apoptosis and cell cycle arrest induction is responsible for aplysinopsin analogs antitumor activity. Hence, our newly synthesized analogs are highly promising candidates for further preclinical studies against prostate cancer.

Identification of aplysinopsin as a blood-brain barrier permeable scaffold for anti-cholinesterase and anti-BACE-1 activity

Aplysinopsins are a group of marine-derived indole alkaloids that display diverse array of pharmacological effects. However, their effect on anti-Alzheimer targets has not been reported. Herein, we report the synthesis of aplysinopsin (1) and its effect on cholinesterases and beta-site amyloid-precursor protein cleaving enzyme 1 (BACE-1). It inhibits electric eel acetylcholinesterase (AChE), equine serum butyrylcholinesterase (BChE), and human BACE-1 with IC₅₀ values of 33.9, 30.3, and 33.7 µM, respectively, and excellent BBB permeability (P_e 8.92 × 10^-6 cm/s). To optimize its sub-micromolar activity, the first-generation analogs were prepared and screened. Two most active analogs 5b and (Z)-8g were found to effectively permeate the BBB (P_e > 5 × 10^-6 cm/s). The N-sulphonamide derivative 5b display better cholinesterase inhibition, whereas the other analog (Z)-8g strongly inhibits BACE-1 (IC₅₀ 0.78 µM) activity. The analog 5b interacts primarily with PAS of AChE, and thus exhibit a mixed-type of inhibition. In addition, aplysinopsin along with new analogs inhibited the self-induced Aβ_1-42 aggregation. The data presented herein indicate that the aplysinopsin-scaffold holds a potential for further investigation as a multi-targeted anti-Alzheimer agent.

Antimicrobial activity of novel 5-benzylidene-3-(3-phenylallylideneamino)imidazolidine-2,4-dione derivatives causing clinical pathogens: Synthesis and molecular docking studies

BACKGROUND

This work is development of new hydantoin molecules as treatment of potential antibacterial and antifungal activity against clinical pathogens causing infectious disease. Synthesized compounds were evaluated in molecular docking studies, the most effective compound is used to dock against the targets of 1U1Z, and 1AI9 kinases, to evaluate its binding affinity, hoping to rationalize and obtain potent of antibacterial, antifungal agents.

MATERIAL AND METHOD

The FTIR, ¹H &¹³C NMR, and mass spectra were used to conform new molecules and their evaluation of antimicrobial activity. Gram-negative bacteria of Pseudomonas aeruginosa (ATCC-27853), Klebsiella pneumoniae (recultured) and Escherichia coli (ATCC-25922), and gram-positive bacteria of Enterococcus faecalis (recultured) and Staphylococcus aureus (ATCC-25923) were evaluated for all compounds. The in vitro antifungal activity was evaluated against Cryptococcus neoformans (recultured), Candida albicans (recultured), Aspergillus niger, Microsporum audouinii (recultured) and Aspergillus fumigatus (recultured) for all synthesized compounds.

RESULT

Antibacterial screening, we identified highly active antimicrobial agents for this study for example; gram-negative bacterial screening of 3g was highly (MIC: 0.25 μg/mL) active in contradiction of P. aeruginosa, whereas bacterial screening of 3e and 3h were more active (MIC: 2 μg/mL) in contradiction of K. pneumoniae and also 3g was more (MIC: 2 μg/mL) active in contradiction of E. faecalis than standard ciprofloxacin. Antifungal activity, the 3b was more active (MIC: 0.25 μg/mL) against C. albicance,3g (MIC: 2 μg/mL) and 3h (MIC: 4 μg/mL) were more potential of A. funigatus, and the compound 3c was highly (MIC: 4 μg/mL) active on M. audouinii than clotrimazole. Molecular docking studies also supported the new finding of potent antimicrobial agents, the compound 3g, 3b, and controls Ciprofloxacin, Clotrimazole were checked again proteins 1U1Z and 1AI9 by Autodock Vina program. The compound 3g was highest binding affinity (-8.4 kcal/mol) than ciprofloxacin (-8.2 kcal/mol) in 1U1Z protein and the compound 3b was highest binding affinity (-8.8 kcal/mol) than clotrimazole (-6.8 kcal/mol) in 1AI9 protein respectively.

CONCLUSION

A novel set of imidazolidine-2,4-dione compounds 3a-h have synthesized and characterized successfully. The screening of antimicrobial activity shows that all compounds possess antimicrobial activities. In addition, the objective of the study was succeeded with a few of the promising molecules, which are proving to be a potential treatment of bacterial infection candidates.

LQFM184: A Novel Wide Ultraviolet Radiation Range Absorber Compound

The use of sunscreen has become an indispensable daily routine since UV radiation is a critical environmental stress factors for human skin. This study focused on the design, synthesis, thermal/chemical stability and efficacy/safety evaluations of a new heterocyclic derivative, namely LQFM184, as a photoprotective agent. The compound showed stability when submitted under oxidative and high-temperature conditions. It also revealed an absorption at 260-340 nm (UVA/UVB), with a main band at 298 nm and a shoulder close to 334 nm. LQFM184 showed capacity to interact with other existing UV filters, promoting an increase in the sun protection factor. In relation to acute toxicity, its estimated LD₅₀ was >300-2000 mg kg^-1 , probably with a low potential of inducing acute oral systemic toxicity hazard. In addition, our data showed that this compound did not have eye irritation, skin sensitization or phototoxicity potentials. Taken together, these findings make LQFM184 a promising ingredient to be used, alone or in association with other UV filters, in cosmetic products such as sunscreens with a broad spectrum of protection.

Tryptophan derived natural marine alkaloids and synthetic derivatives as promising antimicrobial agents

Antimicrobial resistance has become a major threat to public health worldwide, as pathogenic microorganisms are finding ways to evade all known antimicrobials. Therefore, the demand for new and effective antimicrobial agents is also increasing. Natural products have always played an important role in drug discovery, either by themselves or as inspiration for synthetic compounds. The marine environment is a rich source of bioactive metabolites, and among them, tryptophan-derived alkaloids stand out for their abundance and by displaying a variety of biological activities, with antimicrobial properties being among the most significant. This review aims to reveal the potential of marine alkaloids derived from tryptophan as antimicrobial agents. Relevant examples of these compounds and their synthetic analogues reported in the last decades are presented and discussed in detail, with their mechanism of action and synthetic approaches whenever relevant. Several tryptophan-derived marine alkaloids have shown potent and promising antimicrobial activities, whether against bacteria, fungi, or virus. Synthetic approaches to many of the compounds have been developed and recent methodologies are proving to be efficient. Even though most of the studies regarding the antimicrobial activity are still preliminary, this class of compounds has proven to be worth of further investigation and may provide useful lead compounds for the development of antimicrobial agents. Overall, marine alkaloids derived from tryptophan are revealed as a valuable class of antimicrobials and molecular modifications in order to reduce the toxicity of these compounds and additional studies regarding their mechanism of action are interesting topics to explore in the future.

The preparation of (4H)-imidazol-4-ones and their application in the total synthesis of natural products

(4H)-Imidazol-4-ones are an important scaffold for a variety of applications, including natural products, medicine, agriculture, and other applications. Over the years, there have been a number of preparations published for the synthesis of imidazol-4-ones. This review discusses the progress made on the synthesis of imidazol-4-ones, and their application towards the total synthesis of a range of imidazol-4-one containing natural products. Emphasis is made on areas of the field that still need progress.

Muscarine, imidazole, oxazole and thiazole alkaloids

Covering: July 2012 to June 2015. Previous review: Nat. Prod. Rep., 2013, 30, 869-915The structurally diverse imidazole-, oxazole-, and thiazole-containing secondary metabolites are widely distributed in terrestrial and marine environments, and exhibit extensive pharmacological activities. In this review the latest progress involving the isolation, biological activities, and chemical and biogenetic synthesis studies on these natural products has been summarized.

Isolation of Acacetin from Calea urticifolia with Inhibitory Properties against Human Monoamine Oxidase-A and -B

Calea urticifolia (Asteraceae: Asteroideae) has long been used as a traditional medicine in El Salvador to treat arthritis and fever, among other illnesses. The chloroform extract of the leaves of C. urticifolia showed potent inhibition of recombinant human monoamine oxidases (MAO-A and -B). Further bioassay-guided fractionation led to the isolation of a flavonoid, acacetin, as the most prominent MAO inhibitory constituent, with IC₅₀ values of 121 and 49 nM for MAO-A and -B, respectively. The potency of MAO inhibition by acacetin was >5-fold higher for MAO-A (0.121 μM vs 0.640 μM) and >22-fold higher for MAO-B (0.049 μM vs 1.12 μM) as compared to apigenin, the closest flavone structural analogue. Interaction and binding characteristics of acacetin with MAO-A and -B were determined by enzyme-kinetic assays, enzyme-inhibitor complex binding, equilibrium-dialysis dissociation analyses, and computation analysis. Follow-up studies showed reversible binding of acacetin with human MAO-A and -B, resulting in competitive inhibition. Acacetin showed more preference toward MAO-B than to MAO-A, suggesting its potential for eliciting selective pharmacological effects that might be useful in the treatment of neurological and psychiatric disorders. In addition, the binding modes of acacetin at the enzymatic site of MAO-A and -B were predicted through molecular modeling algorithms, illustrating the high importance of ligand interaction with negative and positive free energy regions of the enzyme active site.

Recent developments on the structure–activity relationship studies of MAO inhibitors and their role in different neurological disorders

Development of MAO inhibitors as effective drug candidates for the management and/or treatment of different neurological disorders.

In vitro structure-activity relationships of aplysinopsin analogs and their in vivo evaluation in the chick anxiety-depression model

Aplysinopsins are tryptophan-derived natural products that have been isolated from a variety of marine organisms and have been shown to possess a range of biological activities. In vitro receptor binding assays showed that of the 12 serotonin receptor subtypes, analogues showed a high affinity for the 5-HT2B and 5-HT2C receptor subtypes, with selectivity for 5-HT2B over 5-HT2C. While no conclusions could be drawn about the number and position of N-methylations, bromination at C-4 and C-5 of the indole ring resulted in greater binding affinities, with Ki's as low as 35 nM. This data, combined with previous knowledge of the CNS activity of aplysinopsin analogs, suggested that these compounds may have potential as leads for antidepressant drugs. Compounds 3c, 3u, and 3x were evaluated in the chick anxiety-depression model to assess their in vivo efficacy. Compound 3c showed a modest antidepressant effect at a dose of 30 nM/kg in the animal model.