Oxadiazoles in medicinal chemistry

Discovery of (3-(4-(2-Oxa-6-azaspiro[3.3]heptan-6-ylmethyl)phenoxy)azetidin-1-yl)(5-(4-methoxyphenyl)-1,3,4-oxadiazol-2-yl)methanone (AZD1979), a Melanin Concentrating Hormone Receptor 1 (MCHr1) Antagonist with Favorable Physicochemical Properties

A novel series of melanin concentrating hormone receptor 1 (MCHr1) antagonists were the starting point for a drug discovery program that culminated in the discovery of 103 (AZD1979). The lead optimization program was conducted with a focus on reducing lipophilicity and understanding the physicochemical properties governing CNS exposure and undesired off-target pharmacology such as hERG interactions. An integrated approach was taken where the key assay was ex vivo receptor occupancy in mice. The candidate compound 103 displayed appropriate lipophilicity for a CNS indication and showed excellent permeability with no efflux. Preclinical GLP toxicology and safety pharmacology studies were without major findings and 103 was taken into clinical trials.

Utilization of Cyanoacetohydrazide and Oxadiazolyl Acetonitrile in the Synthesis of Some New Cytotoxic Heterocyclic Compounds

A (pyridazinyl)acetate derivative was reacted with thiosemicarbazide and hydrazine hydrate to yield spiropyridazinone and acetohydrazide derivatives, respectively. The acetohydrazide derivative was used as a starting material for synthesizing some new heterocyclic compounds such as oxoindolinylidene, dimethylpyrazolyl, methylpyrazolyl, oxopyrazolyl, cyanoacetylacetohydrazide and oxadiazolylacetonitrile derivatives. The behavior of the cyanoacetylacetohydrazide and oxadiazolylacetonitrile derivatives towards nitrogen and carbon nucleophiles was investigated. The assigned structures of the prepared compounds were elucidated by spectral methods (IR, ¹H-NMR (13)C-NMR and mass spectroscopy). Some of the newly prepared compounds were tested in vitro against a panel of four human tumor cell lines, namely hepatocellular carcinoma (liver) HePG-2, colon cancer HCT-116, human prostate cancer PC3, and mammary gland breast MCF-7. Also they were tested as antioxidants. Almost all of the tested compounds showed satisfactory activity.

Investigating the Influence of (Deoxy)fluorination on the Lipophilicity of Non-UV-Active Fluorinated Alkanols and Carbohydrates by a New log P Determination Method

Property tuning by fluorination is very effective for a number of purposes, and currently increasingly investigated for aliphatic compounds. An important application is lipophilicity (log P) modulation. However, the determination of log P is cumbersome for non-UV-active compounds. A new variation of the shake-flask log P determination method is presented, enabling the measurement of log P for fluorinated compounds with or without UV activity regardless of whether they are hydrophilic or lipophilic. No calibration curves or measurements of compound masses/aliquot volumes are required. With this method, the influence of fluorination on the lipophilicity of fluorinated aliphatic alcohols was determined, and the log P values of fluorinated carbohydrates were measured. Interesting trends and changes, for example, for the dependence on relative stereochemistry, are reported.

Base-mediated one-pot synthesis of 1,2,4-oxadiazoles from nitriles, aldehydes and hydroxylamine hydrochloride without addition of extra oxidant

The one-pot reactions include sequential base-mediated treatment of amidoxime with an aldehyde to form 4,5-dihydro-1,2,4-oxadiazole, and oxidization of the 4,5-dihydro-1,2,4-oxadiazole by another aldehyde to afford 1,2,4-oxadiazole.

Pyrrolo[3,4-c]pyridine-1,3(2H)-diones: A Novel Antimycobacterial Class Targeting Mycobacterial Respiration

High-throughput screening of a library of small polar molecules against Mycobacterium tuberculosis led to the identification of a phthalimide-containing ester hit compound (1), which was optimized for metabolic stability by replacing the ester moiety with a methyl oxadiazole bioisostere. A route utilizing polymer-supported reagents was designed and executed to explore structure-activity relationships with respect to the N-benzyl substituent, leading to compounds with nanomolar activity. The frontrunner compound (5h) from these studies was well tolerated in mice. A M. tuberculosis cytochrome bd oxidase deletion mutant (ΔcydKO) was hyper-susceptible to compounds from this series, and a strain carrying a single point mutation in qcrB, the gene encoding a subunit of the menaquinol cytochrome c oxidoreductase, was resistant to compounds in this series. In combination, these observations indicate that this novel class of antimycobacterial compounds inhibits the cytochrome bc1 complex, a validated drug target in M. tuberculosis.

Discovery of high affinity inhibitors of Leishmania donovani N-myristoyltransferase

N-Myristoyltransferase (NMT) is a potential drug target in Leishmania parasites. Scaffold-hopping from published inhibitors yielded the serendipitous discovery of a chemotype selective for Leishmania donovani NMT; development led to high affinity inhibitors with excellent ligand efficiency. The binding mode was characterised by crystallography and provides a structural rationale for selectivity.

Antioxidant and anti-inflammatory properties of 1,2,4-oxadiazole analogs of resveratrol

The chemopreventive properties of resveratrol are ascribed mostly to its antioxidant activity, in particular its scavenging ability for reactive oxygen species (ROS), and to the inhibition of NF-κB pathway which has also been suggested as an important underlying mechanism of its reported properties. In present study, a small library of nine 1,2,4-oxadiazole-based structural analogs of resveratrol were assayed for their antioxidant and anti-inflammatory activities. Several compounds showed significant inhibitory activities against NF-κB and/or ROS production. Compound 2, incorporating two para-hydroxyphenyl moieties connected by the 1,2,4-oxadiazole ring, was the most active, its potency in inhibiting activation of NF-κB and ROS scavenging abilities surpassing that of resveratrol. Additionally, we elucidated the mechanisms underlying the NF-κB inhibitory activity of compound 2. Finally, in contrast to resveratrol, compound 2 significantly reduced the LPS-induced release of pro-inflammatory cytokines, indicating its prominent anti-inflammatory potential.

Synthesis and SAR of Imidazo[1,5-a]pyridine derivatives as 5-HT4 receptor partial agonists for the treatment of cognitive disorders associated with Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease which has a higher prevalence and incidence in older people. The need for improved AD therapies is unmet. The 5-hydroxytryptamine4 receptor (5-HT4R) partial agonists may be of benefit for both the symptomatic and disease-modifying treatment of cognitive disorders associated with AD. Herein, we report the design, synthesis and SAR of imidazo[1,5-a] pyridine derivatives as 5-HT4R partial agonists. The focused SAR, optimization of ADME properties resulted the discovery of compound 5a as potent, selective, brain penetrant 5-HT4 partial agonist as a lead compound with good ADME properties and efficacy in both symptomatic and disease modifying animal models of cognition.

Quantitative and qualitative analysis of the novel antitumor 1,3,4-oxadiazole derivative (GLB) and its metabolites using HPLC-UV and UPLC-QTOF-MS

Fructose-based 3-acetyl-2,3-dihydro-1,3,4-oxadiazole (GLB) is a novel antitumor agent and belongs to glycosylated spiro-heterocyclic oxadiazole scaffold derivative. This research first reported a simple, specific, sensitive and stable high performance liquid chromatography-ultraviolet detector (HPLC-UV) method for the quantitative determination of GLB in plasma. In this method, the chromatographic separation was achieved with a reversed phase C18 column. The calibration curve for GLB was linear at 300 nm. The lower limit of quantification was 10 ng/mL. The precision, accuracy and stability of the method were validated adequately. This method was successfully applied to the pharmacokinetic study in rats for detection of GLB after oral administration. Moreover, the structures of parent compound GLB and its two major metabolites M1 and M2 were identified in plasma using an ultra performance liquid chromatography-electrospray ionization-quadrupole-time of flight- mass spectrometry (UPLC-ESI-QTOF-MS) method. Our results indicated that the di-hydroxylation (M1) and hydroxylation (M2) of GLB are the major metabolites. In conclusion, the present study provided valuable information on an analytical method for the determination of GLB and its metabolites in rats, can be used to support further developing of this antitumor agent.

Novel N-Acetyl Bioisosteres of Melatonin: Melatonergic Receptor Pharmacology, Physicochemical Studies, and Phenotypic Assessment of Their Neurogenic Potential

Herein we present a new family of melatonin-based compounds, in which the acetamido group of melatonin has been bioisosterically replaced by a series of reversed amides and azoles, such as oxazole, 1,2,4-oxadiazole, and 1,3,4-oxadiazole, as well as other related five-membered heterocycles, namely, 1,3,4-oxadiazol(thio)ones, 1,3,4-triazol(thio)ones, and an 1,3,4-thiadiazole. New compounds were fully characterized at melatonin receptors (MT1R and MT2R), and results were rationalized by superimposition studies of their structures to the bioactive conformation of melatonin. We also found that several of these melatonin-based compounds promoted differentiation of rat neural stem cells to a neuronal phenotype in vitro, in some cases to a higher extent than melatonin. This unique profile constitutes the starting point for further pharmacological studies to assess the mechanistic pathways and the relevance of neurogenesis induced by melatonin-related structures.

Discovery of Novel Multiacting Topoisomerase I/II and Histone Deacetylase Inhibitors

Designing multitarget drugs remains a significant challenge in current antitumor drug discovery. Because of the synergistic effect between topoisomerase and HDAC inhibitors, the present study reported the first-in-class triple inhibitors of topoisomerase I/II and HDAC. On the basis of 3-amino-10-hydroxylevodiamine and SAHA, a series of hybrid molecules was successfully designed and synthesized. In particular, compound 8c was proven to be a potent inhibitor of topoisomerase I/II and HDAC with good antiproliferative and apoptotic activities. This proof-of-concept study also validated the effectiveness of discovering triple topoisomerase I/II and HDAC inhibitors as novel antitumor agents.

Structure-activity relationship studies and in vivo activity of guanidine-based sphingosine kinase inhibitors: discovery of SphK1- and SphK2-selective inhibitors

Sphingosine 1-phosphate (S1P) is a pleiotropic signaling molecule that acts as a ligand for five G-protein coupled receptors (S1P1-5) whose downstream effects are implicated in a variety of important pathologies including sickle cell disease, cancer, inflammation, and fibrosis. The synthesis of S1P is catalyzed by sphingosine kinase (SphK) isoforms 1 and 2, and hence, inhibitors of this phosphorylation step are pivotal in understanding the physiological functions of SphKs. To date, SphK1 and 2 inhibitors with the potency, selectivity, and in vivo stability necessary to determine the potential of these kinases as therapeutic targets are lacking. Herein, we report the design, synthesis, and structure-activity relationship studies of guanidine-based SphK inhibitors bearing an oxadiazole ring in the scaffold. Our studies demonstrate that SLP120701, a SphK2-selective inhibitor (Ki = 1 μM), decreases S1P levels in histiocytic lymphoma (U937) cells. Surprisingly, homologation with a single methylene unit between the oxadiazole and heterocyclic ring afforded a SphK1-selective inhibitor in SLP7111228 (Ki = 48 nM), which also decreased S1P levels in cultured U937 cells. In vivo application of both compounds, however, resulted in contrasting effect in circulating levels of S1P. Administration of SLP7111228 depressed blood S1P levels while SLP120701 increased levels of S1P. Taken together, these compounds provide an in vivo chemical toolkit to interrogate the effect of increasing or decreasing S1P levels and whether such a maneuver can have implications in disease states.

2,5-Diaryl-1,3,4-oxadiazoles as selective COX-2 inhibitors and anti-inflammatory agents

A new series of compounds comprising of 2,5-diaryl-1,3,4-oxadiazoles was synthesized and evaluated as potential COX-2 inhibitors.

Discovery of highly potent triazoleantifungal agents with piperidine-oxadiazole side chains

A series of novel triazole antifungal agents containing piperidine-oxadiazole side chains were designed and synthesized. Compound 11b was highly active against Candida albicans with a MIC value of 0.016 μg mL⁻¹.

On-water, catalyst-free and room-temperature construction of 2-aryl-1,3,4-oxadiazole derivatives from 1,1-dichloro-2-nitroethene and hydrazides

The image of construction of 2-aryl-1,3,4-oxadiazole derivatives from 1,1-dichloro-2-nitroethene and hydrazides.

Synthesis of fusidic acid bioisosteres as antiplasmodial agents and molecular docking studies in the binding site of elongation factor-G

Structural modifications through bioisosteric approach yielded fusidic acid analogues with 2–35 folds increase in antiplasmodial activity as compared to fusidic acid.

Novel 1,3,4-oxadiazole motifs bearing a quinoline nucleus: synthesis, characterization and biological evaluation of their antimicrobial, antitubercular, antimalarial and cytotoxic activities

Quinoline–oxadiazole hybrids: a new class of antimicrobial, antitubercular and antimalarial compounds.

A facile approach to synthesize 3,5-disubstituted-1,2,4-oxadiazoles via copper-catalyzed-cascade annulation of amidines and methylarenes

A tandem Cu-catalyzed oxidation–amination–cyclization reaction for synthesizing various 3,5-disubstituted-1,2,4-oxadiazoles from easily available amidines and methylarenes or methylhetarenes is reported.

Asymmetric 1,3,4-oxadiazole derivatives containing naphthalene and stilbene units: synthesis, optical and electrochemical properties

Six novel asymmetric 1,3,4-oxadiazole derivatives containing naphthalene and stilbene units have been efficiently synthesized and characterized by FT-IR, (1)H NMR, (13)C NMR, mass spectrometry and elemental analysis. The UV-vis absorption maximum wavelength, fluorescence excitation wavelength, fluorescence emission wavelength and fluorescence quantum yield were measured in dilute tetrahydrofuran solution. The solvent effect was also studied. The HOMO and LUMO levels of these compounds were calculated by density functional theory (DFT) (B3LYP, 6-31G(*)) method and cyclic voltammetry. They emit bright violet to blue emission with high fluorescence quantum yields (0.23-0.94) and large Stokes shifts (53-102 nm). These compounds possess high HOMO levels (-5.03 to -5.17 eV) and suitable band gaps, indicating that they could be benefit for hole injection. The results show that they have a potential for application in optoelectronic materials.

2-(5-Methyl-1,3,4-oxa-diazol-2-yl)phenyl acetate

In the title compound, C₁₁H₁₀N₂O₃, which is a potential bioactive compound, the benzene and oxa­diazole rings are approximately coplanar, with an inter-ring dihedral angle of 4.14 (2)°, while the ester plane is rotated out of the benzene plane [dihedral angle = 82.69 (9)°]. In the crystal, the mol­ecules form layers down the a axis with weak π–π inter­actions between the oxa­diazole and benzene rings [minimum ring centroid separation = 3.7706 (14) Å].