Synthesis, anti-inflammatory and antimicrobial activities of new 1,2,4-oxadiazoles peptidomimetics

New Potential Biologically Active Compounds: Synthesis and Characterization of Urea and Thiourea Derivativpes Bearing 1,2,4-oxadiazole Ring

Background:

Urea, thiourea, and 1,2,4-oxadiazole compounds are of great interest due to their different activities such as anti-inflammatory, antiviral, analgesic, fungicidal, herbicidal, diuretic, antihelminthic and antitumor along with antimicrobial activities.

Objective:

In this work, we provide a new series of potential biologically active compounds containing both 1,2,4-oxadiazole and urea/thiouprea moiety.

Materials and Methods:

Firstly, 5-chloromethyl-3-aryl-1,2,4-oxadiazoles (3a-j) were synthesized from the reaction of different substituted amidoximes (2a-j) and chloroacetyl chloride in the presence of pyridine by conventional and microwave-assisted methods. In the conventional method, 1,2,4-oxadiazoles were obtained in two steps. O-acylamidoximes obtained in the first step at room temperature were heated in toluene for an average of one hour to obtain 1,2,4-oxadiazoles. The yields varied from 70 to 96 %. 1,2,4-oxadiazoles were obtained under microwave irradiation in a single step in a 90-98 % yield at 160 °C in five minutes. 5-aminomethyl-3-aryl-1,2,4- oxadiazoles (5a-j) were obtained by Gabriel amine synthesis in two steps from corresponding 5-chloromethyl-3- aryl-1,2,4-oxadiazoles. Finally, twenty new urea (6a-j) and thiourea (7a-j) compounds bearing oxadiazole ring were synthesized by reacting 5-aminomethyl-3-aryl-1,2,4-oxadiazoles with phenyl isocyanate and isothiocyanate in tetrahydrofuran (THF) at room temperature with average yields (40-70%).

Results and Discussions:

An efficient and rapid method for the synthesis of 1,2,4-oxadiazoles from the reaction of amidoximes and acyl halides without using any coupling reagent under microwave irradiation has been developed, and twenty new urea/thiourea compounds bearing 1,2,4-oxadiazole ring have been synthesized and characterized.

Conclusion:

We have synthesized a new series of urea/thiourea derivatives bearing 1,2,4-oxadiazole ring. Also facile synthesis of 3,5-disubstituted 1,2,4-oxadiazoles from amidoximes and acyl chlorides under microwave irradiation was reported. The compounds were characterized using FTIR, 1H NMR, 13C NMR, and elemental analysis techniques.

Reactions of 3-(p-substituted-phenyl)-5-chloromethyl-1,2,4-oxadiazoles with KCN leading to acetonitriles and alkanes via a non-reductive decyanation pathway

The present work describes an unfamiliar reaction of 5-(chloromethyl)-3-substituted-phenyl-1,2,4-oxadiazoles with KCN affording trisubstituted 1,2,4-oxadiazol-5-ylacetonitriles and their parent alkanes, namely, 1,2,3-trisubstituted-1,2,4-oxadiazol-5-ylpropanes. To the best of our knowledge, the current synthetic route leading to decyanated products will be the first in terms of a decyanation process which allows the transformation of trisubstituted acetonitriles into alkanes by the incorporation of KCN with the association of in situ-formed HCN and most likely through the extrusion of cyanogen which could not be detected or isolated. In addition, the plausible mechanisms were proposed for both transformations. The structures of the title compounds were identified by means of IR, ¹H NMR, ¹³C NMR, 2D NMR spectra, TOF–MS and X-ray measurements.

Synthesis and crystal structure of new heterocyles derived from saccharin and uracil carrying 1,2,4-oxadiazolylmethyl group

Saccharin, uracil, and 1,2,4-oxadiazole heterocyles are important in terms of exhibiting various biological acitivities. In this work, four series of 1,2,4-oxadiazolylmethyl-substituted saccharin, and uracil derivatives are synthesized and their structures are identified by means of spectral/physical characteristics. The first series are oxadiazolylmethyl-substituted saccharins. The second one is oxadiazole-substituted uracils which are obtained as a separable mixture of both mono- and bis-substituted end products. Third series is obtained from 5-amino uracil and chloromethyl oxadiazoles. The fourth group is oxadiazolyl methyl-substituted imino uracils. The structures of some title compounds are also confirmed by X-ray diffraction data.

Synthesis and crystal structure of new heterocycles containing 1,2,4-oxadiazole, 1,2,4-oxadiazolone (thione), hydantoin, and mercaptobenzimidazole units

A number of 1,2,4-oxadiazolone and mercapto nitro benzimidazole derivatives containing 1,2,4-oxadiazole and hydantoin moieties have been prepared, and their structures were identified by means of spectral/physical characteristics including X-ray diffraction data.

Synthesis and anti-protozoal activity of novel dihydropyrrolo[3,4-d][1,2,3]triazoles

1,2,4-Oxadiazole and 1,2,3-triazole containing heterocyclic compounds continue to gain interest in synthesis of chemical entities and exhibit various biological activities as anti-protozoal and anti-cancer agents. By using the principle of bioisosterism, a series of novel oxadiazolyl pyrrolo triazole diones; namely, (3aS,6aR)-1-((3-(4-substituted phenyl)-1,2,4-oxadiazol-5-yl)methyl)-5-phenyl-1,6a-dihydropyrrolo[3,4-d][1,2,3] triazole-4,6(3aH,5H)-diones (5a-k) was designed and synthesized by the 1,3-dipolar cycloaddition reaction of novel 5-azidomethyl 3-aryl substituted 1,2,4-oxadiazoles (4a-k) with N-phenyl maleimide. The structures of all the cycloadducts were elucidated by means of spectroscopic methods and physical characteristics. The in vitro anti-protozoal and cytotoxic activities of these novel heterocyclic compounds were investigated.

Ultrasound-promoted synthesis of 3-trichloromethyl-5-alkyl(aryl)-1,2,4-oxadiazoles

The alternative synthesis of 12 1,2,4-oxadiazoles using ultrasound irradiation from trichloroacetoamidoxime and acyl chlorides is reported. Seven of them are novel compounds. The 3-trichloromethyl-5alkyl(aryl)-1,2,4-oxadiazoles have been synthesised in better yields and shorter reaction times compared to the conventional method. This protocol can be applicable for preparation of 1,2,4-oxadiazoles containing aryl or alkyl groups attached at their C-5 side-chain.

Convenient synthesis and biological profile of 5-amino-substituted 1,2,4-oxadiazole derivatives

We describe herein a convenient straightforward synthesis of 5-amino-substituted 1,2,4-oxadiazoles, upon the reactions of amidoximes with carbodiimides, as well as their further derivatization to acetamides, in good yields. Most of the compounds exhibited in general low interaction with the stable radical 1,1-diphenyl-2-picryl-hydrazyl. Compounds 32 and 39 inhibited significantly soybean lipoxygenase. Selected compounds were screened for their in vivo anti-inflammatory activity using the carrageenin paw edema model and showed significant anti-inflammatory activity (26, 51%). The ability of the compounds to release NO in the presence of a thiol factor has been also investigated.

First ultrasound-mediated one-pot synthesis of N-substituted amides

Ultrasound irradiation, an efficient and innocuous technique of reagent activation for synthesizing organic compounds, has been applied with success to transform seven carboxylic acids to fourteen secondary amides in good to excellent yields. The reaction has worked well either with aryl or alkyl carboxylic acids as well as with aromatic or aliphatic amines. This methodology is expeditious and reliable for preparing secondary carboxamides which in many cases are embedded in the C-5 side-chain of 1,2,4-oxadiazoles (14, 15, 17-27). The elemental analyses of new compounds (19-27) in conjunction with the spectral data of all synthesized amides gave an idea about their structures, while the crystallographic data of one of the compounds (26) supplied information concerning the configurational behavior of the amidic part and also the conformational aspect of the entire molecule in the crystalline state.

An Efficient One-Pot Synthesis of 5-(substituted amino)-1,2,4-thia- and -oxa-diazoles

A general protocol for the synthesis of 5-(substituted amino)-1,2,4-thiadiazoles by the cyclocondensation reaction of amidoximes with N-substituted thioureas in the presence of KF/Al2O3, and of 5-(cyclohexylamino)-1,2,4-oxadiazoles with DCC in the presence of KF/Al2O3 and thiourea, is described. The structures of the new compounds were elucidated by spectroscopic and physical data, and the crystal structure determination by X-ray diffraction of three examples.

Synthesis of glycosyl-triazole linked 1,2,4-oxadiazoles

The synthesis of four different types of oxadiazoles containing a terminal acetylenic group is described. Reaction of these oxadiazoles with various azidoglycosides via a copper-catalyzed [3+2] cycloaddition ('click chemistry') afforded the corresponding glycosyl-triazole linked 1,2,4-oxadiazoles in good yields.

Synthesis of aminoacyl thiaolidones as potential antitumour agents

In the scope of a research program aiming to perform the synthesis and pharmacological evaluation of novel possible antitumour prototype compounds, we report in this paper the synthesis of new peptidyl derivatives from 4-thiazolidone nucleus. The synthesis reactions have been performed based in peptide synthesis as strategies. The characterisation of this new class of compounds was performed with IR and (1)H-NMR spectroscopy. In vivo, antitumour activity tests showed that some of these compounds were able to inhibit significantly sarcoma S-180 tumour growth in mice, revealing itself as a new potential class of drugs in cancer chemotherapy.

Genotoxic activity of 3-[3-phenyl-1,2,4-oxadiazol-5-yl] propionic acid and its peptidyl derivatives determined by Ames and SOS response tests

Compounds derived from 1,2,4-oxadiazole have being reported for their anti-inflammatory activity. However, those compounds should be devoid of any genotoxic side effect. In this work, the genotoxic activity of peptidomimetic moiety-containing 1,2,4-oxadiazoles derivatives was tested based on the Ames and SOS Chromotest. The results showed no mutagenic activity on the Ames test for 3-[3-phenyl-1,2,4-oxadiazol-5-yl] propionic acid (POPA) parental drug, but a weak SOS response induction on Chromotest. The chemical modifications reduced that response to a non-significative level, with l-phenylalanine peptidomimetic derivative being showing the lowest induction response. The results pointed out for the effectiveness of promoting chemical modifications of biological active compounds to increase its mode of action, showed in previous work, without increasing and even decreasing its DNA damage effect.