Anti-inflammatory properties of Neowerdermannia vorwerkii Frič 'Achacana' used in treating stomach-related ailments

ETHNO-PHARMACOLOGICAL RELEVANCE

The tuber of Neowerdermannia vorwerkii commonly known as 'Achacana' is used as an infusion in Andean countries to treat various gastrointestinal ailments, kidney and liver diseases.

AIM OF THE STUDY

This study determined the anti-inflammatory activity of the aqueous extract from Neowerdermannia vorwerkii and identified the compounds related to this activity.

MATERIALS AND METHODS

A bio-guided isolation of the active compounds of Neowerdermannia vorwerkii was carried out, selecting the sub-extracts and fractions depending on their anti-inflammatory activity in the Hs 738.St/Int, Hs 746T and NCI-N87 cells.

RESULTS

Three compounds were obtained and characterised by nuclear magnetic resonance and mass spectrometry. These compounds are (3-(pyridin-3-yl)-5-(tiophen-3-yl)-1,2,4-oxadiazole (1), 5-(3-methoxyphenyl)-3-(pyridin-3-yl)-1,2,4-oxadiazole (2) and 5-(3-hydroxyphenyl)-3-(pyridin-3-yl)-1,2,4-oxadiazole (3). Regarding their anti-inflammatory activity, the three compounds inhibited the production of cytokines (IL-1β, IL-6 and TNF-α), however, compound 1 was the most active, with an IC₅₀ of 0.87 μM in all cell lines.

CONCLUSION

In the present study, the anti-inflammatory activity of the aqueous extract of Neowerdermannia vorwerkii was tested and analysed, following the isolation of three 1,2,4-oxadiazoles type compounds with similar pharmacological properties.

A review on synthetic account of 1,2,4-oxadiazoles as anti-infective agents

Most of the currently marketed drugs consist of heterocyclic scaffolds containing nitrogen and or oxygen as heteroatoms in their structures. Several research groups have synthesized diversely substituted 1,2,4-oxadiazoles as anti-infective agents having anti-bacterial, anti-viral, anti-leishmanial, etc. activities. For the first time, the present review article will provide the coverage of synthetic account of 1,2,4-oxadiazoles as anti-infective agents along with their potential for SAR, activity potential, promising target for mode of action. The efforts have been made to provide the chemical intuitions to the reader to design new chemical entity with potential of anti-infective activity. This review will mark the impact as the valuable, comprehensive and pioneered work along with the library of synthetic strategies for the organic and medicinal chemists for further refinement of 1,2,4-oxadiazole as anti-infective agents.

1,2,4-Oxadiazole topsentin analogs as staphylococcal biofilm inhibitors targeting the bacterial transpeptidase sortase A

The inhibition or prevention of biofilm formation represents an emerging strategy in the war against antibiotic resistance, interfering with key players in bacterial virulence. This approach includes the inhibition of the catalytic activity of transpeptidase sortase A (Srt A), a membrane enzyme responsible for covalently attaching a wide variety of adhesive matrix molecules to the peptidoglycan cell wall in Gram-positive strains. A new series of seventeen 1,2,4-oxadiazole derivatives was efficiently synthesized and screened as potential new anti-virulence agents. The ability of inhibiting biofilm formation was evaluated against both Gram-positive and Gram-negative pathogens. Remarkably, all these compounds inhibited S. aureus and/or P. aeruginosa biofilm formation in a dose dependent manner, with 50% biofilm inhibitory concentrations (BIC_50s) below 10 μM for the most active compounds. Inhibition of SrtA was validated as one of the possible mechanisms of action of these new 1,2,4-oxadiazole derivatives, in the tested Gram-positive pathogen, using a specific enzymatic assay for a recombinant S. aureus SrtA. The three most active compounds, eliciting BIC₅₀ values for S. aureus ATCC 25923 between 0.7 and 9.7 μM, showed a good activity toward the enzyme eliciting IC₅₀ values ranging from 2.2 to 10.4 μM.

Synthesis and SAR studies of novel 1,2,4-oxadiazole-sulfonamide based compounds as potential anticancer agents for colorectal cancer therapy

A diverse series of 1,2,4-oxadiazoles based substituted compounds were designed, synthesized and evaluated as anticancer agents targeting carbonic anhydrase IX (CAIX). Initial structure-activity analysis suggested that the thiazole/thiophene-sulfonamide conjugates of 1,2,4-oxadiazoles exhibited potent anticancer activities with low μM potencies. Compound OX12 exhibited antiproliferative activity (IC₅₀ = 11.1 µM) along with appreciable inhibition potential for tumor-associated CAIX (IC₅₀ = 4.23 µM) isoform. Therefore, OX12 was structurally optimized and its SAR oriented derivatives (OX17-27) were synthesized and evaluated. This iteration resulted in compound OX27 with an almost two-fold increase in antiproliferative effect (IC₅₀ = 6.0 µM) comparable to the clinical drug doxorubicin and significantly higher potency against CAIX (IC₅₀ = 0.74 µM). Additionally, OX27 treatment decreases the expression of CAIX, induces apoptosis and ROS production, inhibited colony formation and migration of colon cancer cells. Our studies provide preclinical rational for the further optimization of identified OX27 as a suitable lead for the possible treatment of CRC.

Design, synthesis and biological evaluation of coumarin linked 1,2,4-oxadiazoles as selective carbonic anhydrase IX and XII inhibitors

A series of coumarin linked 1,2,4-oxadiazoles were synthesized and the synthesized compounds were subjected for evaluation against the four physiologically and pharmacologically relevant hCA isoforms, hCA I, II, IX and XII. Upon evaluation of the results, it was inferred that the coumarin linked 1,2,4-oxadiazoles showed selective hCA IX and XII inhibition (low to medium nanomolar range) over hCA I and II (>10000 nM). The inhibition constants ranged from low nanomolar to moderately nanomolar. Compounds 6o, 6a, 6q and 6c elicited hCA XII inhibition, with K_i values lower than that of the standard, Acetazolamide (AAZ) with compound 6o exhibiting a K_i value of 1 nM., against hCA IX, the compound 6c exhibited the most potent inhibition with a K_i value of 23.6 nM. Hence, compound 6o can be taken as an effective lead compound for the development of hCA XII inhibitors and compound 6c can be taken as a lead compound for the development of dual hCA IX and XII inhibitors. To understand the molecular interactions, the two most potent compounds 6a and 6o were docked within the hCA XII catalytic cleft in order to study their binding modes with that isoform.

1,2,4-Oxadiazole derivatives targeting EGFR and c-Met degradation in TKI resistant NSCLC

Development of small-molecule agents with the ability to facilitate oncoprotein degradation has emerged as a promising strategy for cancer therapy. Since EGFR and c-Met are both implicated in oncogenesis and tumor progression, we initiated a screening program by using an in-house library to identify agents capable of inducing the concomitant suppression of EGFR and c-Met expression, which led to the identification of compound 1, a 1,2,4-oxadiazole derivative. Based on the scaffold of 1, we developed a series of derivatives to assess their efficacies in facilitating the downregulation of EGFR and c-Met, among which compound 48 represented the optimal agent. 48 showed equipotent antiproliferative activity against a panel of five NSCLC cell lines with different EGFR mutational status (IC₅₀ = 0.2-0.6 μM), while the same panel exhibited differential sensitivity to different EGFR kinase inhibitors tested. Cell cycle analysis indicated that the antiproliferative activity of 48 was associated with its ability to cause G2/M arrest and, to a lesser extent, apoptosis. Western blot and RT-PCR analyses revealed that 48 facilitated the downregulation of EGFR and c-Met at the protein level. In vivo data showed that oral administration of 48 was effective in suppressing gefitinib-resistant H1975 xenograft tumor growth in nude mice, and at a suboptimal dose, could sensitize H1975 tumors to gefitinib. Based on these findings, 48 represents a promising candidate for further development to target EGFR TKI-resistant NSCLC via dual inhibition of EGFR and c-Met oncoproteins.

Novel 5-(quinuclidin-3-ylmethyl)-1,2,4-oxadiazoles to investigate the activation of the α7 nicotinic acetylcholine receptor subtype: Synthesis and electrophysiological evaluation

α7 nicotinic acetylcholine receptors (nAChRs) are relevant therapeutic targets for a variety of disorders including neurodegeneration, cognitive impairment, and inflammation. Although traditionally identified as an ionotropic receptor, the α7 subtype showed metabotropic-like functions, mainly linked to the modulation of immune responses. In the present work, we investigated the structure-activity relationships in a set of novel α7 ligands incorporating the 5-(quinuclidin-3-ylmethyl)-1,2,4-oxadiazole scaffold, i.e. derivatives 21a-34a and 21b-34b, aiming to identify the structural requirements able to preferentially trigger one of the two activation modes of this receptor subtype. The new compounds were characterized as partial and silent α7 nAChR agonists in electrophysiological assays, which allowed to assess the contribution of the different groups towards the final pharmacological profile. Overall, modifications of the selected structural backbone mainly afforded partial agonists, among them tertiary bases 27a-33a, whereas additional hydrogen-bond acceptor groups in permanently charged ligands, such as 29b and 31b, favored a silent desensitizing profile at the α7 nAChR.

Exploration of diphenylalkyloxadiazoles as novel cardiac myosin activator

To explore novel cardiac myosin activator, a series of diphenylalkyl substituted 1,3,4-oxadiazoles and 1,2,4-oxadiazoles have been prepared and tested for cardiac myosin ATPase activation in vitro. In all cases, three carbon spacer between the oxadiazole core and one of the phenyl ring was considered crucial. In case of 1,3,4-oxadiazole, zero to two carbon spacer between oxadiazole core and other phenyl ring are favorable. Phenyl ring can be replaced by cyclohexyl moiety. In case of 1,2,4-oxadiazole, zero or one carbon spacer between the oxadiazole and other phenyl ring are favorable. Introduction of hydrogen bonding donor (NH) group at the 2^nd position of the 1,3,4-oxadiazole enhances the activity. Substitutions on either of the phenyl rings or change of phenyl ring to other heterocycle are not tolerated for both the oxadiazoles. The prepared oxadiazoles showed selective activation for cardiac muscle over smooth and skeleton muscles.

Conjugation of N-acylhydrazone and 1,2,4-oxadiazole leads to the identification of active antimalarial agents

Malaria, caused by several Plasmodium species, is the major life-threatening parasitic infection worldwide. Due to the parasite resistance to quinoline based drugs, the search for antimalarial agents is necessary. Here, we report the structural design, synthesis and antiparasitic evaluation of two novel series of 1,2,4-oxadiazoles in conjugation to N-acylhydrazones, both groups recognized as privileged structures, as well as the studies on the antimalarial activity of 16 previous described analogues. By varying substituents attached to the phenyl ring, it was possible to retain, enhance or increase the antiparasitic activity in comparison to the nonsubstituted derivatives. Replacement of substituted aryl rings by ferrocenyl and cinnamyl moieties attached in the N-acylhydrazone ablated the antiparasitic response, evidencing the structural features associated with the activity. Active compounds exhibited in vitro potency similar to mefloquine, but not all inhibited β-hematin formation. Additionally, the active compounds displayed low cytotoxicity in HepG2 cells and did not cause hemolysis in uninfected erythrocytes. In Plasmodium berghei-infected mice, the compounds reduced parasitemia but exhibited limited efficacy in increasing mice survival when compared to chloroquine, suggesting that pharmacological improvement is still necessary.

N-heterocyclic carbenes (NHC) with 1,2,4-oxadiazole-substituents related to natural products: synthesis, structure and potential antitumor activity of some corresponding gold(I) and silver(I) complexes

This work presents the synthesis, characterization and application of eleven new gold (I) complexes 13-23 with 1,2,4-oxadiazole-containing N-heterocyclic carbene (NHC) ligands and of the NHC silver(I) complex 24. The 1,2,4-oxadiazole unit, which can be found in a variety of biologically active natural products such as phidianidines or quisqualic acid, was incorporated, along with a variety of other biologically active moieties (anthracene, indole, 2-pyridine, 2,3,4,5-tetra-O-acetyl-D-glucopyranose, quincorine and quincoridine), in order to change the lipophilicity of the complexes, so that the transport of the active units (M-NHC) though the cell wall barrier is facilitated. The biological activity of the complexes was investigated. In vitro assessment of anti-tumor activity in a panel of 12 human tumor cell lines by a monolayer assay revealed impressive potency (mean IC50 < 0.1 μM) and tumor selectivity for 6 compounds, with individual IC50 values in the low nanomolar range. The solid state structures of compounds 13, 14, 15, 17, 18, 19 and 24 were determined by X-ray diffraction analyses.

Exploration of the structure-activity relationship of 1,2,4-oxadiazole antibiotics

We have recently disclosed the discovery of the class of 1,2,4-oxadiazole antibiotics, which emerged from in silico docking and scoring efforts. This class of antibacterials exhibits Gram-positive activity, particularly against Staphylococcus aureus. We define the structure-activity relationship (SAR) of this class of antibiotics with the synthesis and evaluation of a series of 59 derivatives with variations in the C ring or C and D rings. A total of 17 compounds showed activity against S. aureus. Four derivatives were evaluated against a panel of 16 Gram-positive strains, inclusive of several methicillin-resistant S. aureus strains. These compounds are broadly active against Gram-positive bacteria.