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A one-pot ambient-temperature procedure for the synthesis of 3,5-disubstituted-1,2,4-oxadiazoles from amidoximes and carboxylic acids under superbase-promoted conditions is reported.

A series of novel aromatic primary sulfonamides decorated with diversely substituted 1,2,4-oxadiazole periphery groups has been prepared using a parallel chemistry approach. The compounds displayed a potent inhibition of cytosolic hCA II and membrane-bound hCA IX isoforms. Due to a different cellular localization of the two target enzymes, the compounds can be viewed as selective inhibition tools for either isoform, depending on the cellular permeability profile. The SAR findings revealed in this study has been well rationalized by docking simulation of the key compounds against the crystal structures of the relevant hCA isoforms.

An efficient and mild one-pot protocol has been developed for the synthesis of 1,2,4-oxadiazoles via the reaction of amidoximes with dicarboxylic acid anhydrides in a NaOH/DMSO medium. The method allows the synthesis of diversely substituted carboxylic acids bearing the 1,2,4-oxadiazole motif, – a popular building block for pharmaceutical research, in moderate to excellent yields. The reaction scope includes aromatic and heteroaromatic amidoximes as well as five-, six- and seven-membered anhydrides. The advantages of this procedure are proven gram-scalability and the use of inexpensive starting materials, which from a process chemistry point of view are essential for future industrial applications.

N-Furfuryl allylamines, readily accessible from corresponding furfurals or furfuryl amines, react with a broad range of arylsulfonyl chlorides with the formation of a 3a,6-epoxyisoindole core in one synthetic stage. Usually, in boiling water, the interaction sequence involves two consecutive steps: the Hinsberg reaction and the intramolecular Diels–Alder furanе (IMDAF) reaction. The scope and limitations of the proposed method were thoroughly investigated, and it was revealed that the key [4 + 2] cycloaddition step proceeds through an exo-transition state, giving rise to the exclusive formation of a single diastereomer of the target heterocycle. The method allows the ability to obtain N-sulfaryl-substituted 3a,6-epoxyisoindoles and 4a,7-epoxyisoquinolines, which are potentially useful substrates for further transformations and subsequent bioscreening, in particular antimicrobial activity.

The monoamine oxidase (MAO) enzymes are key metabolic enzymes of neurotransmitter and other bioactive amines, and represent important drug targets for the treatment of neuropsychiatric and neurodegenerative disorders. Inhibitors of MAO are established medications for the treatment of depression and Parkinson’s disease, and may have future roles in other disease states such as the therapy of prostate cancer, cardiovascular disease and inflammatory diseases. Based on these considerations, the present study synthesizes a series of 22 pyrazolo[1,5-a]quinoxalin-4-one derivatives and evaluated them as potential inhibitors of human MAO-A and MAO-B. The results show that 8 derivatives inhibit MAO-A, and 3 derivatives inhibit MAO-B with IC50 values in the submicromolar range (

An expanded set of pyridazine-containing benzene sulfonamides was investigated for inhibition of four human carbonic anhydrase isoforms, which revealed a pronounced inhibition trend toward hCA IX, a cancer-related, membrane-bound isoform of the enzyme. Comparison of antiproliferative effects of these compounds against cancer (PANC-1) and normal (ARPE-19) cells at 50 μM concentration narrowed the selection of compounds to the eight which displayed selective growth inhibition toward the cancer cells. More detailed investigation in concentration-dependent mode against normal (ARPE-19) and two cancer cell lines (PANC-1 and SK-MEL-2) identified two lead compounds one of which displayed a notable cytotoxicity toward pancreatic cancer cells while the other targeted the melanoma cells. These findings significantly expand the knowledge base concerning the hCA IX inhibitors whose inhibitory potency against a recombinant enzyme translates into selective anticancer activity under hypoxic conditions which are aimed to model the environment of a growing tumor.

Series of structurally diverse 2-imidazoline derivatives have been synthesized by condensation of substituted aldehydes with ethylenediamine, Pd-catalyzed N-arylation of 2-imidazolines and by the formation of 1,2,4-oxadiazoles and benzoxazepines from 2-imidazoline-containing precursors. The 2-imidazoline derivatives were evaluated as potential inhibitors of human monoamine oxidase (MAO) A and B. Among the 2-imidazolines, good potency inhibitors were discovered with compound 9p (IC50 = 0.012 µM) being the most potent MAO-B inhibitor, while compound 9d (IC50 = 0.751 µM) was the most potent MAO-A inhibitor of the series. These potencies are in the same range as those of reference MAO inhibitors used in the clinic. Among 33 compounds evaluated, 13 exhibited IC50 values in the submicromolar range for the inhibition of an MAO isoform. It is postulated that the imidazoline moieties of some of these inhibitors may be recognized by the imidazoline I2-binding site of MAO. Good potency MAO inhibitors may be useful for the treatment of neuropsychiatric and neurodegenerative disorders such as depression and Parkinson’s disease, and future application for the treatment of prostate cancer, congestive heart failure and Alzheimer’s disease. In addition, high potency 2-imidazoline-derived MAO inhibitors may be used as potential probes for the imidazoline binding sites of the MAOs, as well as to determine alternative binding regions of imidazoline within the MAO active site.

An expanded set of diversely substituted 1,2,4-oxadiazole-containing primary aromatic sulfonamides was synthesized and tested for inhibition of human carbonic anhydrase I, II, IX and XII isoforms. The initial biochemical profiling revealed a significantly more potent inhibition of cancer-related, membrane-bound isoform hCA IX (reaching into submicromolar range), on top of potent inhibition of hCA XII that is another cancer target. The observed structure-activity relationships have been rationalized by molecular modeling. Comparative single-concentration profiling of the carbonic anhydrase inhibitors synthesized for antiproliferative effects against normal (ARPE-19) and cancer (PANC-1) cell lines under chemically induced hypoxia conditions revealed several candidate compounds selectively targeting cancer cells. More in-depth characterization of these leads revealed two structurally related compounds that showed promising selective cytotoxicity against pancreatic cancer (PANC-1) and melanoma (SK-MEL-2) cell lines.

The imidazolin-1-yl azine moiety, constructed using a recently developed Buchwald–Hartwig-type arylation methodology, displays excellent chemical stability under subsequent microwave-assisted Pd-catalyzed amination with a range of N-nucleophiles. This finding extends the usage of imidazolin-1-yl azines for bioactive compound library design. The latter is exemplified herein by the discovery of micromolar kinase inhibitors.

A simple and convenient one-pot method is reported for the synthesis of (E)-3-(3-aryl(heteroaryl, alkyl)-1,2,4-oxadiazole-5-yl)acrylic acids utilizing readily accessible or commercially available substituted benzamidoximes and inexpensive exo-3,6-epoxy-1,2,3,6-tetrahydrophthalic anhydride. The method is based on the reaction of amidoximes with the anhydride in a basic medium at RT followed by an acid-catalyzed retro-Diels-Alder reaction. The observed stereoselective heterocyclization/retro-Diels-Alder cascade process is suitable for the synthesis of a wide range of substituted (E)-1,2,4-oxadiazole-5-ylacrylic acids featuring electron donating and electron withdrawing groups on the aryl moiety, as well as heteroaryl or alkyl substituents at position 3 of the 1,2,4-oxadiazole ring (42–79%; 15 examples).

The present study investigates the monoamine oxidase (MAO) inhibition properties of a series of ten 5-aryl-1,3,4-oxadiazol-2-ylbenzenesulfonamides. The target compounds were synthesized by dehydration of the corresponding N,N′-diacylhydrazines with phosphorus oxychloride to yield the 1,3,4-oxadiazole cycle with concomitant transformation of the sulfonamide to the sulfonyl chloride group. Treatment with aqueous ammonia in acetonitrile regenerated the target sulfonamides. The results of the enzymology document that these compounds are potent and specific MAO-B inhibitors with the most potent compound exhibiting an IC50 value of 0.0027 µM. An analysis of the structure-activity relationships shows that the 4-benzenesulfonamides are significantly more potent MAO-B inhibitors than the corresponding 3-benzenesulfonamides, and that the corresponding N,N′-diacylhydrazine synthetic precursors are weak MAO inhibitors. Although MAO inhibition by oxadiazole compounds are known, this is the first report of nanomolar MAO inhibition potencies recorded for sulfonamide derivatives. MAO-B specific inhibitors such as those discovered here may be of interest in the treatment of neurodegenerative disorders such as Parkinson’s disease.

Replacement of amide moiety with the 1,2,4-oxadiazole core in the scaffold of recently reported efflux pump inhibitors afforded a novel series of oxadiazole/2-imidazoline hybrids. The latter compounds exhibited promising antibacterial activity on both Gram-positive (Staphylococcus aureus, Bacillus subtilis) and Gram-negative (Escherichia coli, Pseudomonas fluorescens) strains. Furthermore, selected compounds markedly inhibited the growth of certain drug-resistant bacteria. Additionally, the study revealed the antiproliferative activity of several antibacterial frontrunners against pancreas ductal adenocarcinoma (PANC-1) cell line, as well as their type-selective monoamine oxidase (MAO) inhibitory profile.