Rajendra M. Srivastava

Synthesis, optical properties and thermal behaviour of 1,3,4‐oxadiazole‐based twin dimers

The synthesis, optical properties and thermal behaviour of five new 1,3,4‐oxadiazole‐based light‐emitting twin dimers are described. The synthesised compounds were obtained in good yields following a convergent synthetic approach. The products 8a–8e display blue fluorescence both in solution and in solid phases. All compounds exhibited dendritic crystalline growth. Furthermore, compound 8b also exhibited liquid crystal properties. Due their high thermal stabilities thin films of 8a–8e could be prepared by thermal evaporation technique. The morphology of the film surface was investigated using atomic force microscopy (AFM).

Non‐symmetrical luminescent 1,2,4‐oxadiazole‐based liquid crystals

Thermal and optical behaviours of a series of highly π‐conjugated hockey stick‐shaped non‐symmetrical 1,2,4‐oxadiazoles, with liquid crystalline properties, have been studied. All of them presented liquid crystalline phases, in particular smectic and nematic phases typical of calamitic compounds. Although these substances are thermally less stable than their 1,3,4‐oxadiazole isomers, they showed better liquid crystalline behaviour with lower melting points. UV–visible spectra of compounds 1a–1f in solution displayed similar absorption patterns with maxima around 320 and 350 nm (ε ∼ 2.0–6.0×104 L mol−1 cm−1). All compounds exhibited strong blue fluorescence ( = 405–468 nm) with large Stokes shift (79–117 nm). The quantum yields (ΦF) are 42–65%, except for compounds 1c and 1f where the yields are 2 and 14%, respectively. These compounds also exhibited blue emission in the solid phase ( = 408–492 nm).

Antiinflammatory property of 3-aryl-5-(n-propyl)-1,2,4-oxadiazoles and antimicrobial property of 3-aryl-5-(n-propyl)-4,5-dihydro-1,2,4-oxadiazoles: Their syntheses and spectroscopic studies

The synthesis of six 3-aryl-5-(n-propyl)-4,5dihydro-1,2,4-oxadiazoles 3a-f has been achieved in a facile manner by the reaction of an appropriate arylamidoxime 1a-f with butyraldehyde 2. Oxidation of 3a-f individually using MnO(2) in CH(2)Cl(2) or sodium hypochlorite in THF/H(2)O furnished 1,2,4-oxadiazoles 4a-f in good to excellent yields. Compounds 4a-f were also evaluated against inflammation. Except 4e, all of them reduced inflammation, however, 4c presented better antiinflammatory activity. A preliminary antimicrobial activity tests of 3a-f showed that these compounds possess activity against some microorganisms. In fact, 3c and 3f have been found to be more effective against Staphylococcus aureus, Mycobacterium smegmatis, and Candida albicans.

Synthesis of 1,2,3-triazole derivatives and in vitro antifungal evaluation on Candida strains.

1,2,3-Triazoles have been extensively studied as compounds possessing important biological activities. In this work, we describe the synthesis of ten 2-(1-aryl-1H-1,2,3-triazol-4-yl)propan-2-ols via copper catalyzed azide alkyne cycloaddition (CuAAc or click chemistry). Next thein vitro antifungal activity of these ten compounds was evaluated using the microdilution broth method against 42 isolates of four different Candida species. Among all tested compounds, the halogen substituted triazole 2-[1-(4-chlorophenyl)-1H-(1,2,3)triazol-4-yl]propan-2-ol, revealed the best antifungal profile, showing that further modifications could be done in the structure to obtain a better drug candidate in the future.

Synthesis and cytotoxic profile of glycosyl–triazole linked to 1,2,4-oxadiazole moiety at C-5 through a straight-chain carbon and oxygen atoms

The convergent synthesis of an unusual (but simple) class of compounds 5a-g has been achieved by the copper-catalyzed [3+2] cycloaddition reaction of 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl azide 4 with propynyl 3-[3-(aryl)-1,2,4-oxadiazol-5-yl] propionates 3a-g. The formerly known azide 4 has been prepared according to the literature procedure; however, the synthesis of esters 3a-g is being reported for the first time. The infrared as well as (1)H NMR spectra of all new products are in agreement with their proposed structures. By carrying out the nOe experiment of one of the final compounds 5a, we have been able to establish that only the 1,4-regioisomers have been formed in the cycloaddition reaction. All final products presented weak cytotoxic activity, but 5e and 5g had somewhat better behaviour showing 22-25% cell growth inhibition against two cell strains: NCI-H(292) (lung carcinoma) and HEp-2 (larynx carcinoma).

Structural investigation of anti-Trypanosoma cruzi 2-iminothiazolidin-4-ones allows the identification of agents with efficacy in infected mice.

We modified the thiazolidinic ring at positions N3, C4, and C5, yielding compounds 6-24. Compounds with a phenyl at position N3, 15-19, 22-24, exhibited better inhibitory properties for cruzain and against the parasite than 2-iminothiazolidin-4-one 5. We were able to identify one high-efficacy trypanocidal compound, 2-minothiazolidin-4-one 18, which inhibited the activity of cruzain and the proliferation of epimastigotes and was cidal for trypomastigotes but was not toxic for splenocytes. Having located some of the structural determinants of the trypanocidal properties, we subsequently wished to determine if the exchange of the thiazolidine for a thiazole ring leaves the functional properties unaffected. We therefore tested thiazoles 26-45 and observed that they did not inhibit cruzain, but they exhibited trypanocidal effects. Parasite development was severely impaired when treated with 18, thus reinforcing the notion that this class of heterocycles can lead to useful cidal agents for Chagas disease.

Microwave-induced synthesis of 2,3-unsaturated O-glycosides under solvent-free conditions

Abstract Microwave irradiation of a mixture of tri- O -acetyl- d -glucal 1 and an appropriate alcohol 2a – f , in the presence of Montmorillonite K-10 as a catalyst, provided unsaturated glycosides 3a – f in much shorter time and in yields comparable with conventional heating.

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.

Synthesis and hypolipidemic activity of N-substituted phthalimides. Part V☆

A series of N-aryl- or N-(1,2,4-triazol-yl)-phthalimides (4a-4i) have been synthesized starting from phthalic anhydride (1) and an appropriate amine (2a-2i). All compounds presented hypolipidemic activity, but compound 4d proved to be the most active and reduced plasma cholesterol and triglyceride levels in Swiss white mice significantly.

Benzamidoximes: structural, conformational and spectroscopic studies. I

Abstract The synthesis and properties of seven arylamidoximes are reported. 1 H- and 13 C-NMR studies and MO calculations were performed on all seven and an X-ray crystallographic determination was done on one, to determine their structure. The theoretical calculations were done using the AM1 and PM3 methods. From these results it is concluded that, for all of the arylamidoximes studied here, the NH 2 group of the amidoxime ( N -hydroxyamidine) has very little sp 2 character and the aryl ring is not coplanar with the amidoxime group. X-ray crystallographic data for p -chlorobenzamidoxime were compared with the theoretically calculated coordinates. It is interesting to note that, in crystals, the –NH 2 group is coplanar with the CN bond and the aryl ring is out of the plane of the amidoxime group. Molecular mechanics (Biosym) calculations on benzamidoxime yielded better coordinates than either the AM1 or PM3 methods.