Synthesis and characterization of new mesogenic esters derived from 1,2,4-oxadiazole and study the effect of alkoxy chain length in their liquid crystalline properties

In this study, a new series of non-symmetrically 3,5-disubstituted of 1,2,4-oxadiazole derivatives, 4-[5-(4-methylphenyl)-1,2,4-oxadiazol-3-yl]-phenyl-4-alkoxybenzoate (G₁–G₁₁), which containing ether and ester linkages in the same molecule, is synthesized using different synthetic procedures and their structures are confirmed by several spectroscopic techniques (FT-IR and ¹H nuclear magnetic resonance). The mesomorphic properties of these compounds are studied by differential scanning calorimetry (DSC) and polarized optical microscopy (POM); all these derivatives exhibited as mesogens and displayed an enantiotropic liquid crystal with nematic texture, the nematogenic phase of these materials was appeared in wide temperature ranges on heating and cooling cycles that were observed by POM and DSC. The influence of 1,2,4-oxadiazole ring and the elongation of alkyl chain in the mesomorphic properties of this series were investigated. The mesogenic behaviour of this series was compared with the compounds possessing a somewhat similar structure.     

Synthesis,characterization and anticancer evaluation of 2-(naphthalen-1-ylmethyl/naphthalen-2-yloxymethyl)-1-[5-(substituted phenyl)-[1,3,4]oxadiazol-2-ylmethyl]-1H-benzimidazole

In the present study o-phenylenediamine and naphtene-1-acetic acid/2-naphthoxyacetic acid were used as a starting material through a series of steps and 2-(naphthalen-1-ylmethyl/Naphthalen-2-yloxymethyl)-1H-benzimidazol-1-yl]acetohydrazide 5a, 5b were obtained. In the first series 1,3,4-oxadiazole derivatives have been synthesized from Schiff base of the corresponding hydrazide i.e. 2-[2-(naphthalen-1-ylmethyl)-1H-benzimidazol-1-yl]acetohydrazide 5a by using Chloramin-T. In the second series 1,3,4-oxadiazole has been synthesized from 2-{2-[(naphthalen-2-yloxy)methyl]-1Hbenzimidazol-1-yl}acetohydrazide 5b by using phosphorous oxychloride and aromatic acid. These compounds were evaluated by IR, NMR, Mass spectrometry, elemental analysis and finally in vitro anticancer evaluation was carried out by NCI 60 Cell screen at a single high dose (10–5 M) on various panel/cell lines. One compound 7c was found to be the most active on breast cancer cell line and compounds 4b and 7d were moderately active.     

New mesogenic materials bearing 1,2,4-oxadiazole moiety: Synthesis,characterization and investigation their mesomorphic behaviors

In this work, two series containing a 1,2,4-oxadiazole ring as a central core were synthesized and characterized by common spectroscopic techniques, including FT-IR, ¹H-NMR, and elemental analysis. The first series was 3-(4-alkoxyphenyl)-5-(p-methylphenyl)-1,2,4-oxadiazole (C_n), which consisted of alkoxy group in the terminal arm and a methyl group in the other, while, the oxidation reaction of methyl group in a series (C_n) to the carboxy group was the method used to synthesize the second series in this work, 4-(3-(4-alkoxyphenyl)-1,2,4-oxadiazol-5-yl)benzoic acid (D_n). The mesophase behaviors of these two series were studied by optical polarized microscopy (OPM) and differential scanning calorimetry (DSC). The liquid crystalline investigations of the compounds (C_n and D_n) show that the last six homologeus of the series (C_n), (C₆–C₁₁), have a monotropic nematic phase, while only the intermediate compounds in the series (D_n), (D₃–D₉), displayed monotropic nematic phase, also, the liquid crystalline properties in the first and last two compounds in this series (D₁, D₂, D₁₀, and D₁₁) had disappeared. The differences in liquid crystalline properties between the two series, (C_n and D_n), were discussed through the influences of the different terminal groups (–CH₃ and –COOH) in addition to the effect of the 1,2,4-oxadiazole ring and the length of the terminal alkyl chain.     

Synthesis and in vitro antibacterial activity of new oxoethylthio-1,3,4-oxadiazole derivatives

In the present investigation, a series of 2(4-pyridyl)-5[(aryl/heteroarylamino)-1-oxoethyl]thio-1,3,4-oxadiazole were synthesized using isonicotinohydrazide and substituted aryl/heteroaryl amines using pyridine as solvent. Newly synthesized compounds were tested for their in vitro anti-tubercular activity against Mycobacterium tuberculosis H37Rv using the BACTEC 460 radiometric system. Among the synthesized compounds, compounds 2(4-pyridyl)-5((2-nitrophenylamino)-1-oxoethyl)thio-1,3,4-oxadiazole (5e), 2(4-pyridyl)-5((4-nitrophenylamino)-1-oxoethyl)thio-1,3,4-oxadiazole (5g) and 2(4-pyridyl)-5((2-pyrrolylamino)-1-oxoethyl)thio-1,3,4-oxadiazole (5k) produced highest efficacy and exhibited >90% inhibition at a concentration of 0.0077, 0.0052 and 0.0089 μM, respectively. All the new compounds were pharmacologically evaluated for their in vitro Antimicrobial activity.     

Synthesis and characterisation of asymmetrical mesogenic materials based on 2,5-disubstituted-1,3,4-oxadiazole

New mesogenic homologous series bearing 1,3,4-oxadiazole ring with a nitro terminal group, 4-(5-(4-nitrophenyl)-1,3,4-oxadiazol-2-yl)phenyl 4-((4-methoxybenzylidene)amino)benzoate (G₁–G₁₁), were synthesised. Their chemical structures are identified by fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance (¹H-NMR) and elemental analysis. The liquid crystalline properties of the series G_n and their precursory F_n were screened by differential scanning calorimetry and optical polarising microscopy (OPM). The compounds of the series G_n were screened by thermogravimetric analysis to observe their thermal stability. The target compounds (G_n) in this study, were displayed different liquid crystalline mesophase, the first two homologous (G₁ and G₂) did not show any liquid crystalline behaviour, the homologous (G₃–G₁₀) which have an alkoxy terminal group (n = 3–10) exhibited nematic phase, whilst the last derivative of the series (G₁₁), n = 12, displayed SmA phase. The mesomorphic properties of these derivatives were affected by the presence of the nitro group at the end of the molecules which was classified as a strong polar group. Also, the role of alkoxy terminal chain and the bent heterocyclic ring (1,3,4-oxadiazole) in the liquid crystalline properties of these molecules were debated.     

Synthesis of 1,2,4-Triazol-3-ylmethyl-, 1,3,4-Oxa-, and -Thiadiazol-2-ylmethyl-1<Emphasis Type="Italic">H</Emphasis>-[1,2,3]-triazolo[4,5-<Emphasis Type="Italic">d</Emphasis>]pyrimidinediones

Summary. 1-Carbethoxymethyl-4,6-dimethyl-1H-[1,2,3]triazolo[4,5-d]pyrimidine-5,7(4H,6H)-dione was synthesized and treated with hydrazine hydrate to give the corresponding hydrazide. The latter hydrazide was treated either with phenylisothiocyanate or with carbon disulfide/alc. KOH to afford the corresponding thiosemicarbazide and oxadiazole derivatives. Alkylation of 2-mercapto-1,3,4-oxadiazole with dimethyl sulfate or ethyl chloroacetate gave the corresponding 2-methylthio-, and 2-ethylthioglycolate derivatives. Formation of 1,3,4-thiadiazole, 5-mercapto-1,2,4-triazole, and 1,3,4-oxadiazole were carried out by treating of the latter thiosemicarbazide with conc. H₂SO₄, NaOH/HCl, and HgO. Treating of 5-mercapto-1,2,4-triazole with ethyl chloroacetate afforded the thioglycolate ester. Hydrolysis of the latter with hydrazine hydrate afforded the hydrazide derivatives. Condensation of these hydrazides with monosaccharide aldoses gave the corresponding sugar hydrazones. The novel compounds were tested for antiviral activity against hepatitis B virus and showed moderate activities.     

Synthesis and characterization of mono- and bicyclic heterocyclic derivatives containing 1,2,4-triazole, 1,3,4-thia-, and -oxadiazole rings

A series of new N- and S-substituted 1,3,4-oxadiazole derivatives were synthesized. 5-Pyridin-3-yl-3-[2-(5-thioxo-4,5-dihydro-l,3,4-thiadiazol-2-yl)ethyl]-1,3,4-oxadiazole-2(3H)-thione and 5-[(5-(pyridin-3-yl)-1,3,4-oxadiazol-2-ylthio)methyl]-N-phenyl-1,3,4-thiadiazol-2-amine were formed by cyclization of 3-(5-pyridin-3-yl-2-thioxo-1,3,4-oxadiazol-3(2H)-ylpropanimidohydrazide and 2-[(5-pyridin-3-yl-1,3,4-oxadiazol-2-yl)thio]thiosemicarbazide with CS₂ and H₂SO₄. On the other hand, a number of new bicyclic 1,2,4-triazolo[3,4-b][1,3,4]thiadiazole derivatives were synthesized. 6-Pyridin-3-ylbis[1,2,4]‐triazolo[3,4-b:4′,3′-d][1,3,4]thiadiazole-3(2H)-thione was synthesized by reaction of 6-(hydrazino)-3-pyridine-3-yl[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole with CS₂/KOH/EtOH. The structures of the newly synthesized compounds were elucidated by the spectral and analytical data IR, Mass, and ¹H NMR spectra. Correspondence: Adel A.-H. Abdel-Rahman, Department of Chemistry, Faculty of Science, Menoufia University, Shebin El-Koam, Egypt; Wael A. El-Sayed, National Research Centre, Department of Photochemistry, Cairo, Egypt.     

6-硝基苯并咪唑杂环衍生物的合成

以６－硝基苯并咪唑－１－乙酰肼和５－（６－硝基苯并咪唑－１－亚甲基）－３－巯基－４－氨基－１,２,４－三唑为原料,在不同条件下合成了一系列新的均三唑〔３,４－ｂ〕－１,３,４－噻二唑,１,２,４－三唑和１,３,４－恶二唑衍生物。化合物的结构均经元素分析、＾１Ｈ ＮＭＲ、ＩＲ和ＭＳ确证,并对其波谱性质进行了讨论。     

Synthesis,characterization and biological activity of Hg(II), Fe(III) complexes with 1,3,4-oxadiazole, 1,2,4-triazole derivatives from L-methionine

Four novel heterocyclic1,3,4-oxadiazole, 1,2,4-triazole derivatives, namely: 5-[1-amino-3-(methylsulfanyl)propyl]-1,3,4-oxadiazole-2(3H)-thione (4), 4-amino-5-[1-amino-3-(methylsulfanyl)propyl]-4H-1,2,4-triazole-3-thiol (5), 1-amino-3-[1-amino-3-(methylsulfanyl)propyl]-1H-1,2,4-triazole-5-thiol (7), and 5-[1-amino-3-(methylsulfanyl)propyl]-1H-1,2,4-triazole-3-thiol (9) have been synthesized from l-methionine and characterized by different spectroscopic techniques (FT-IR, UV–Vis, ¹H NMR, ¹³C NMR and MS). Complex formation with Hg⁺⁺ and Fe⁺⁺⁺ ions were formed from the four heterocyclic 4, 5, 7 and 9. The antimicrobial activities for synthetic intermediates and final four products were assisted using paper disk diffusion method against Gram-negative bacteria: Escherichia coli, Pseudomonas aeroginosae and Gram-positive bacteria: Staphylococus aureus 25923, Staphylococus aureus 43300 and showed variant activity against some of the microorganisms tested.     

Synthesis and pharmacological evaluation of 3-diphenylmethyl-6-substituted-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazoles: A condensed bridgehead nitrogen heterocyclic system

A series of 3-diphenylmethyl-6-substituted-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazole derivatives (4a–j and 5a–d) were synthesized by condensation of 4-amino-5-diphenylmethyl-4H-1,2,4-triazole-3-thiol with various substituted aromatic acids and aryl/alkyl-isothiocyanates. The structures of synthesized compounds were characterized by elemental analysis, IR, ¹H NMR, ¹³C NMR and mass spectroscopic studies. These compounds were tested in vivo for their anti-inflammatory activity. The compounds which showed activity comparable to the standard drug ibuprofen were screened for their analgesic, ulcerogenic, lipid peroxidation and hepatotoxic effects. Compounds 6-(4-chlorophenyl)-3-diphenylmethyl-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazole (4a) and 6-(2,4-dichlorophenyl)-3-diphenylmethyl-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazole(4c) emerged as the most active compounds of the series and were moderately more potent than the standard drug ibuprofen.     

Synthesis and pharmacological evaluation of 3-[5-(aryl-[1,3,4]oxadiazole-2-yl]-piperidine derivatives as anticonvulsant and antidepressant agents

In the present study, we have synthesized a series of fifteen nipecotic acid 1,3,4-oxadiazole based hybrids with significant (60–78%) yields. All the compounds were characterized by using different spectroanalytical techniques such as FT-IR, ¹H NMR, ¹³C NMR, and elemental analysis. This design strategy was validated by using in vivo anti-epileptic and anti-depressant bioassay models. Anti-convulsant activity was evaluated using subcutaneous pentylenetetrazol (scPTZ) in mice and MES induced seizure. Among a spectrum of activities, three compounds (4i, 4m, and 4n) displayed significant activity against pentylenetetrazole (scPTZ) induced seizures. No disruptions in motor co-ordination were observed in mice pretreated with the test compounds in the rotarod test. Their influence on the safety profile of elevated serum levels of biochemical markers such as hepatic and renal toxicity has been found to be safe. The derivatives also show marked anti-depressant activity, devoid of serotonergic augmentation as assessed using the despair swim test, 5-hydroxytryptophan (5-HTP)-induced head twitch test and learned helplessness test. In silico docking studies targeted on homology modelled GABA transporter 1 (GAT1) protein shows the critical enzyme-ligand interactions leading to the inhibition of the GAT1 transporter. The compound 4m was found to be the most active compound among all the synthesized compounds.     

One-potCuAAC synthesis of (1H-1,2,3-triazol-1-yl)methyl-1,3,4/1,2,4-oxadiazoles starting from available chloromethyl-1,3,4/1,2,4-oxadiazoles

The one-pot CuAAC synthesis of (1H-1,2,3-triazol-1-yl)methyl-1,3,4-oxadiazole and (1H-1,2,3-triazol-1-yl)methyl-1,2,4-oxadiazole derivatives via three-component reaction of consequent nucleophilic substitution of chlorine, with azide, and its further “click” reaction, with alkynes, in the presence of CuI was studied. The utility of newly synthesized 2-(azidomethyl)-1,3,4/1,2,4-oxadiazoles and chloromethyl-1,3,4/1,2,4-oxadiazole derivatives was explored, and their limitations were determined. Novel 5-([4-aryl-1H-1,2,3-triazol-1-yl]methyl)-3-(aryl)-1,2,4-oxadiazoles, 2-([4-aryl-1H-1,2,3-triazol-1-yl]methyl)-5-(aryl)-1,3,4-oxadiazoles were obtained in good yields.     

Synthesis,characterization and pharmacological evaluation of some new 1,3,4-oxadiazole derivatives bearing 3-chloro-2-fluoro phenyl moiety

A new series of 2-(3-chloro-2-fluorophenyl)-5-aryl-1,3,4-oxadiazole (3a–j) and 2-(aryl sulfanyl)-5-(3-chloro-2-fluorophenyl)-1,3,4-oxadiazole (5a–e) were synthesized via a multistep reaction from 3-chloro-2-fluoro benzoic acid. The newly synthesized compounds were characterized by IR, ¹H NMR, ¹³C NMR, mass spectral data and elemental analysis. They were also screened for their in vivo anti-convulsant and anti-inflammatory activities. Some of them exhibited significant biological activities and were well supported by in silico molecular docking studies for the inhibition of cyclooxygenase-2 (PDB ID: 1CX2) and voltage-gated sodium channels (PDB ID: 4F4L) comparable with the standard drugs. Thus, they were believed to be good inhibitors of cyclooxygenase-2 (PDB ID: 1CX2) and voltage-gated sodium channels (PDB ID: 4F4L).     

Synthesis,spectroscopic and crystal structure investigation of [Cu(bzsmp)2Cl2];{bzsmp = 2-benzylsulfanyl-5-(2-methoxyphenyl)-1,3,4-oxadiazole}: cyclization of N-[bis(benzylsulfanyl)methylene]-2-methoxybenzohydrazide to 2-benzylsulfanyl-5-(2-methoxyphenyl)-1,3,4 -oxadiazole during complexation

The ligand N²-[bis(benzylsulfanyl)methylene]-2-methoxybenzohydrazide (N²-bmbh) (1) on reaction with CuCl₂.2H₂O yielded the mononuclear complex [Cu(bzsmp)₂Cl₂] (2) (2-benzylsulfanyl-5-(2-methoxyphenyl)-1,3,4-oxadiazole, bzsmp). Complex 2 has been characterized by analytical, spectroscopic and X-ray data. X-ray study of 2 reveals that the cyclized ligand 2-benzylsulfanyl-5-(2-methoxyphenyl)-1,3,4-oxadiazole (bzsmp) acts as neutral bidentate ligand to form six membered chelate ring and the presence of C–H?π (face to edge) and C–H?S and two type of C–H?Cl weak interactions.     

Design,synthesis, and characterization of some new benzimidazole derivatives and biological evaluation

A new series of benzimidazole derivatives ( 1-15 ) containing 1,2,4-triazole, 1,3,4-thiadiazole, 1,3,4-oxadiazole, and thiazolidinon rings have been synthesized. All new synthesized benzimidazole compounds were confirmed by ¹H NMR, ¹³C NMR spectra, and LC-MS, and they were examined for their antioxidant and antimicrobial activities. Compounds 7 and 1 showed the highest and the lowest antioxidant activities, respectively. The lowest minimum inhibition concentration value found in compound 5 against Enterobacter aerogenes.     

Polyamides with pendant 1,3,4-oxadiazole and pyridine moieties

A novel aromatic diamine,2-（5-（3,5-diaminophenyl）-l,3,4-oxadiazole-2-yl）pyridine（POBD）,containing a pyridine ring and a 1,3,4-oxadiazole moiety,was synthesized.It was used in a polycondensation with various aromatic and aliphatic diacid chlorides to generate a series of new aromatic polyamides with pendant 1,3,4-oxadiazole groups.The prepared polyamides were characterized by IR,elemental analysis and through the synthesis of model compounds.Thermophysical properties of the synthesized polyamides have been studied by DSC,TGA and inherent viscosity measurements. Relatively high inherent viscosity values（0.76-1.62 dL/g,in 0.125%H₂SO₄ at 25℃） were observed for these compounds. Number average molecular weight（M_n） of the polymers was measured by vapor phase osmometry（VPO）.The introduction of bulky side chains in the structure of aromatic polyamides led to increased solubility of these polymers in common polar and aprotic solvents,such as DMF,DMSO,NMP and DMAc,which allowed thin films to be cast from polymer solutions. The highest molecular weight（M_n = 51190） was observed for polymer（DC）,which was prepared from pyridine-2,6-dichlorocarbonyl.     

Synthesis and comparative study of the heterocyclic rings on liquid crystalline properties of 2,5-aryl-1,3,4-oxa(thia)diazole derivatives containing furan and thiophene units

A series of heterocyclic liquid crystalline compounds containing 1,3,4-oxadiazole/thiadiazole, furan and thiophene units were synthesised and characterised by means of electrospray ionisation-mass spectrometry (ESI-MS), high-resolution mass spectroscopy (HRMS), ¹H nuclear magnetic resonance (NMR) and ¹³C NMR. The thermal behaviours were investigated by differential scanning calorimetry (DSC) and polarised optical microscopy (POM). The effect of the 1,3,4-oxadiazole, 1,3,4-thiadiazole, furan, thiophene and benzene rings on the liquid crystalline properties was discussed briefly in context with the geometrical and electronic factors. The results showed that the tendency to form mesophases follows the sequence: 1,4-disustituted benzene >2,5-disubstituted thiophene >2,5-disustituted furan and 1,3,4-thiadiazole >1,3,4-oxadiazole.     

Columnar mesophases and phase behaviors of novel polycatenar mesogens containing bi-1,3,4-oxadiazole

A new series of liquid-crystalline bi-1,3,4-oxadiazole derivatives (2,2′-bis(3,4,5-trialkoxyphenyl)-bi-1,3,4-oxadiazole, BOXD-Tn, n=3, 4, 5, 6, 7, 8, 10, 14) were designed and synthesized. They have been confirmed to give rise to columnar mesophases. The columnar mesophases for BOXD-Tn (n=5, 6, 7, 8, 10) could be supercooled to −20 °C on the cooling runs. A room temperature Col_ho phase was obtained for BOXD-T14. All BOXD-Tn exhibit good fluorescence properties either in cyclohexane or in solid state.     

含吡啶环的1,3,4-噁二唑衍生物的合成及生物活性研究

依据生物电子等排原理,在分子中同时引入吡啶环和1,3,4-噁二唑杂环合成了5-(3-吡啶基或4-吡啶基)-1,3,4-噁二唑2-硫乙酸胺类化合物,用¹HNMR,IR,质谱和元素分析对其结构进行了表征.离体试验表明,化合物B1-5小麦赤霉病菌和苹果轮纹病菌的抑制率分别为30%和42%,化合物B1-6对苹果轮纹病菌的抑制率为38%.除草活性实验结果表明,化合物B1-6对油菜和稗草具有较高的抑制作用.     

Thermally stable polymers containing 1,3,4-oxadiazole units obtained from Huisgen reaction

Thermally stable polymers containing 1,3,4-oxadiazole units have been synthesized through Huisgen reaction of the aromatic/aliphatic bis-tetrazole compounds with the aromatic/aliphatic bis-acid chlorides in pyridine as solvent.The obtained polymers are insoluble or slightly soluble even in polar aprotic solvents such as DMSO and DMF.Relatively high inherent viscosity values（0.61-1.33 dL/g,in 0.125%H₂SO₄ at 25℃） were observed for these compounds.Thermal analyses of the polymers using DSC and TGA techniques showed that the polymers have improved thermal stabilities.The glass transition temperature has not been observed in the fully aromatic polymers,but the polymers obtained from 5-[6-（1H-tetrazol -5-yl）hexyl]-lH-tetrazole（Ⅳ） showed very clear T_g.A model reaction was also investigated and the resulting bis-1,3,4-oxadiazole compound was characterized by conventional spectroscopy methods.