New liquid crystals derived from thiophene connected to the 1,2,3-triazole heterocycle

In this work, six new compound derivatives from thiophene were synthesised. The three symmetrical compounds were synthesised containing two heterocyclic 1,2,3-triazole on each side of thiophene, 2,5-disubstituted and the three non-symmetrical compounds were synthesised containing alkyne groups as a spacer in replacing one of these heterocycles. The structural modifications were made by changing the number of alkoxy groups in order to understand the relation between structure and mesomorphic behaviour. Some of the compounds presented liquid crystalline properties, smectic and nematic mesophases. The non-symmetrical compounds allowed for a low emission in the blue region.     

Synthesis of non-symmetrically substituted 1,2,4-oxadiazole derived liquid crystals

Non-symmetrically substituted 1,2,4-oxadiazole derived bent-core liquid crystals have been synthesized by a simple and straightforward synthetic method. All these compounds exhibit enantiotropic nematic phases over exceptionally wide temperature ranges.     

Synthesis of luminescent liquid crystals derived from gallic acid containing heterocyclic 1,3,4-oxadiazole

This article describes the synthesis, liquid crystalline and photophysical properties of luminescent liquid crystalline compounds, derived from gallic acid containing heterocyclic 1,3,4-oxadiazole. The mesophases of these compounds were characterised using polarising optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). All compounds showed high thermal stability and blue photoluminescence in solution, with emission maxima between 376 and 381 nm. For all compounds, the liquid crystalline behaviour was preserved on cooling from the isotropic state to room temperature. These characteristics make these materials good candidates for application in organic electronics.     

Fluorescent liquid crystalline compounds with 1,3,4-oxadiazole and benzo[b]thiophene units

A series of fluorescent liquid crystalline compounds containing 1,3,4-oxadiazole and benzo[b]thiophene units have been prepared. In CH₂Cl₂ solution, these compounds displayed a fluorescent emission with λ_max at 422–426 nm and quantum yields of 41–48%. Most of them exhibited thermotropic liquid crystalline properties with nematic and/or smectic A phases with excellent thermal stability. This work revealed that longer terminal alkoxy chains would be detrimental to the formation of mesophases for such kind of compounds. The effect of the terminal groups on mesomorphic and spectroscopic property is discussed.     

Synthesis,characterisation and mesomorphic behaviours of non-symmetrically substituted 1,2,4- and 1,3,4-oxadiazole derivatives

Two series of non-symmetrically substituted bent-core mesogens derived from the central 3,5 and 2,5 cores of the 1,2,4- and 1,3,4-oxadiazole derivatives, respectively, containing ether and ester linkage have been synthesised by several straightforward synthetic procedures, and their mesomorphic behaviour was studied by optical polarising microscopy (OPM) and differential scanning calorimetry (DSC). The last five homologues of the 1,2,4-oxadiazole series exhibit a monotropic nematic phase on cooling, while the 1,3,4-oxadiazole derivatives do not show any liquid crystalline properties but rather a crystal to isotropic transition is observed by OPM. We show that the bent angles of the 1,2,4- and 1,3,4-oxadiazole rings are crucial in observing the liquid crystal (LC) phases formed, and also that the length of the alkyl substituent is observed to have a significant effect on the nature of the LC phases.     

1,2,4-噁二唑类化合物的合成及抗菌活性研究

以对溴苯腈为原料,通过多步反应合成了一系列3-(吗啉苯基)-5-取代-1,2,4-异噁唑类化合物和3-(吗啉苯基)-5-取代-4,5-二氢-1,2,4-噁二唑类化合物,并用1HNMR、13C NMR和MS进行了结构确证。这些化合物对测试的部分革兰氏阳性菌,如金黄色葡萄球菌、耐甲氧西林金黄色葡萄球菌、表皮葡萄球菌、粪肠球菌显示出一定的抗菌活性,但与噁唑烷酮类上市药物利奈唑胺相比,抗菌活性有明显下降。这一结果表明对于化合物的抗菌活性,1,2,4-噁二唑杂环不如噁唑烷酮结构有效。     

New isothiocyanato liquid crystals containing thieno[3,2-b]thiophene central core

New isothiocyanato liquid crystal (LC) materials based on thieno[3,2-b]thiophene core have been synthesised and characterised. Their mesomorphic and physical properties were evaluated. The results indicate that most of the new compounds exhibit only enantiotropic smectic A phases with high clearing points, and the difluorinated compounds (A3 and A6), in particular, also display a stable nematic phase with low melting points. Compared with the corresponding biphenyl and thiophene-phenyl analogues, these thieno[3,2-b]thiophene-based compounds possess increased birefringence (the highest value found to be 0.40) and mesogenic phase intervals. These new thieno[3,2-b]thiophene-based LCs exhibit a high birefringence and a high clearing point and are of potential use as components of high birefringence mixtures.     

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.     

Non-symmetric liquid crystal dimers based on 1,3,4-oxadiazole derivatives: synthesis,photoluminescence and liquid crystal behaviour

A series of non-symmetric liquid crystal compounds consisting of two different semi-rigid anisometric cores, namely 1,3,4-oxidiazole and biphenyl units, and two short terminal groups, have been synthesised in good yield. It has been shown by polarising optical microscopy and differential scanning calorimetry that all these compounds display liquid crystalline behaviour, with nematic and/or smectic A mesophases. The nature of the mesophases is dependent on the electronic properties of the terminal groups. In methylene chloride solution all the compounds displayed a room temperature emission with λ_max at 358–396 nm and quantum yields of 0.29–0.56. The effect of the terminal groups on the mesomorphic and photoluminescent properties is briefly discussed in the context of their electronic characteristics.     

Focused microwave irradiation-assisted synthesis of N-cyclohexyl-1,2,4-oxadiazole derivatives with antitumor activity

A facile synthesis of 3,5-disubstituted 1,2,4-oxadiazole derivatives under focused microwave irradiation (FMWI) is reported. Arylamidoximes 1a–i and dicyclohexylcarbodiimide (DCC) were carried out in DMF under FMWI to obtain 1,2,4-oxadiazoles 2a–i in 61–81% yields. All compounds exhibited antiproliferative activities in vitro against three human cancer cell lines HCT-116, PC-3, and SNB-19.     

Cyclization of protected N-acylhydroxyguanidine to 3-amino-1,2,4-oxadiazole

The acid mediated cyclization of a protected N-acylhydroxyguanidine into the corresponding 3-amino-1,2,4-oxadiazole and confirmation of its structure by single crystal X-ray crystallography is reported herein. The yield of the cyclization is comparable to literature reports utilizing alternative procedures. Importantly, these new conditions provide complementary chemoselectivity to current synthetic procedures which may be useful for the synthesis of 3-amino-1,2,4-oxadiazoles in general.     

Macrodiscotic liquid crystals derived from planar phthalocyanine oligomers

A novel unsymmetrically substituted phthalocyanine, which contains an extended planar core and a pair of adjacent peripheral hydroxyl groups is synthesised and used to prepare planar phthalocyanine oligomers. These materials act as macrodiscotic liquid crystals giving a columnar mesophase, which is stable over a large temperature range.     

Chiral banana liquid crystals derived from sugars

This paper describes the synthesis and physical properties of a chiral bent-core liquid crystal containing the chiral non-aromatic central ring system 1,5-anhydro-2-desoxy-D-arabino-hexitol. The preparation involved a stepwise construction of the mesogenic side chains via a selective diesterification of glucal at positions three and six with 4-O-acetylbenzoyl chloride followed by selective deacetylation. Repeated esterification of the aromatic hydroxy group with a substituted benzoic acid and hydrogenation of the double bond resulted in the desired product. To our knowledge, this is the first banana shaped liquid crystal synthesized containing a sugar derivative as a chiral core. Investigation of the mesogenic properties and electro-optic experiments showed traditional calamitic phases along with banana phases.     

Polycyclic systems containing 1,2,4-oxadiazole ring 2. 4-(1,2,4-Oxadiazol-5-yl)pyrrolidin-2-ones: Synthesis and prediction of biological activity

A one-pot condensation of 5-oxopyrrolidine-3-carboxylic acids, carbonyldiimidazole, and benzamidoximes leads to the formation of the novel 4-(1,2,4-oxadiazol-5-yl)pyrrolidin-2-one bicyclic systems, the structures of which have been confirmed by IR and ¹H NMR methods and by liquid chromato-mass spectrometry. The results of a PASS prediction of the biological activity of the synthesized compounds are presented. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 758–764, May, 2008.     

Hexagonal columnar mesophases of polycatenar para-phenylene connected bis-oxadiazole-based liquid crystals

In this article polycatenar liquid crystals containing two 1,3,4-oxadiazoles interconnected by a para-substituted benzene ring as the central linking unit and three alkoxy chains at each terminal have been synthesised, and investigated by polarising microscopy, DSC and XRD scattering. Molecules with medium chain length form exclusively hexagonal columnar liquid crystalline phases.     

Model studies on the structure of poly(amide oxime)s and their cyclodehydration reactions leading to poly(1,2,4-oxadiazole)s

To obtain an understanding of the low molecular weight character of wholly aromatic poly(1,4-arylene acyldiamide oxime)s (PAAs) having n-alkyloxymethyl side braches and the additional decrease in molecular weight during their cyclodehydration reaction leading to the corresponding poly(1,4-arylene-1,2,4-oxadiazole)s (PAOs), tautomeric structures of poly[1,4-phenylene-2,5-bis(n-octyloxymethyl)terephthaldiamide oxime] (C₈-PAA) were ¹H-NMR-spectroscopically investigated by using two model compounds: O,O'-dibenzoyl terephthaldiamide oxime (H-PAA-M, 4) and O,O'-dibenzoyl-2,5-bis(n-octyloxymethyl) terephthaldiamide oxime (C₈-PAA-M, 5). In solution H-PAA-M existed exclusively as oximino isomer, while C₈-PAA-M consisted only of imino tautomer and C₈-PAA contained both the oximino and imino form, the former being dominant in composition. It was found that the presence of imino tautomer caused serious effects both on the low molecular weight character of C₈-PAA and on the additional decrease in molecular weight during thermal cyclodehydration to C₈-PAO, whereas the presence of oximino tautomer showed practically little effect. A discussion on the results is provided from mechanistic viewpoint. © 1993 John Wiley & Sons, Inc.     

Ultrasound-assisted,one-pot,three-component synthesis and antibacterial activities of novel indole derivatives containing 1,3,4-oxadiazole and 1,2,4-triazole moieties

Thirteen novel indole derivatives were efficiently synthesized through ultrasound irradiation by using 4-amino-5-(1H-indol-3-yl)-4H-[1,2,4]triazole-3-thiol (8) and 2-mercapto-5-substituted-1,3,4-oxadiazoles (5a–m). Compared with conventional and microwave methods, yields increased to 82–93%, and reaction times decreased to 15–35 min. The structures of these novel compounds were characterized by spectral data and elemental analysis. Two out of the synthesized compounds (10f and 10l) exhibited excellent activity against Staphylococcus aureus and Escherichia coli, and thus warrant further research.     

Non-symmetrically (1,2,4- and 1,3,4-)oxadiazole homologous: synthesis,characterisation and study the effect of different substituents on their mesophase behaviours

We have previously demonstrated that the type of oxadiazole isomers is relatively affected on showing the liquid crystalline properties of the compounds that have the same chemical compositions. In this paper, we presented the synthesis and mesomorphic behaviour of related compounds that possess ester linkage with different substituted groups on para of the phenyl to six derivatives containing 1,3,4-oxadiazole and like another six containing 1,2,4-oxadiazole rings. The formation of these compounds was evidenced by FTIR, ¹H NMR, ¹³C NMR, elemental analysis and mass techniques. Their mesophase behaviours were studied by optical polarised microscopy (OPM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). All of them presented liquid crystalline properties with nematic (N), smectic A (SmA) and smectic C (SmC) phases typically to calamitic compounds. The effect of substituent group nature and the type of oxadiazole isomers on the liquid crystalline properties of these compounds are analysed and discussed.     

5-嘧啶基-1,2,4-噁二唑衍生物的合成及生物活性研究

通过嘧啶甲酰氯与取代的苄胺肟反应得到一系列结构新颖的5-嘧啶基-1,2,4-噁二唑类化合物,并对其结构进行了表征,培养并测定了化合物5a的晶体结构;将目标化合物晶体结构对接到靶酶酵母乙酰辅酶A羧化酶(ACCase)的活性位点,发现目标化合物与复合物晶体中的禾草灵分子的构象及结合模式相似;初步生物活性测试表明部分化合物具有较好的除草活性.     

新型噻吩席夫碱及其酯化产物合成与性能

以噻吩为起始原料,对工艺进行了优化合成出噻吩-2-甲醛,并由噻吩-2-甲醛与4-氨基苯酚缩合反应生成未见报道的噻吩-2-甲醛缩4-氨基苯酚席夫碱,进一步由DCC/DMAP高效酯化法与十一烯酸进行酯化反应。通过用纸片法测试了该席夫碱抑菌活性,结果表明具有较好的抑制作用;并通过偏光显微镜对酯化产物进行研究,观察到了较好的液晶相织构。