Uncatalyzed synthesis of new substituted dihydro-2H-dipyrimido[1,2-a,4,5-d]pyrimidine-2,4(3H)-dione

Research on Chemical Intermediates - A convenient and new method has been developed for the synthesis of highly substituted dihydro-2H-dipyrimido[1,2-a,4,5-d]pyrimidine-2,4(3H)-dione derivatives by...     

Syntheses of New Unsymmetrical 2,5‐Disubstituted‐1,3,4‐oxadiazoles and 1,2,4‐Triazolo[3,4‐b]‐1,3,4‐thiadiazoles Bearing Thieno[2,3‐c]pyrazolo Moiety

New series of (thieno[2,3‐c]pyrazolo‐5‐yl)‐[1,2,4]triazolo[3,4‐b][1,3,4]thiadiazoles 10a , 10b , 10c and (thieno[2,3‐c]pyrazol‐5‐yl)‐1,3,4‐oxadiazol‐3(2H)‐yl)ethanones 6a , 6b , 6c has been synthesized from thieno[2,3‐c]pyrazole‐5‐carbohydrazide 3 by multistep reaction sequence. (5‐Aryl‐1,3,4‐oxadiazol‐2‐yl)‐1H‐thieno[2,3‐c]pyrazoles 4a , 4b , 4c were also synthesized from thieno[2,3‐c]pyrazole‐5‐carbohydrazide 3 by cyclization with various aromatic carboxylic acids. The hydrazide 3 was obtained by reaction of thieno[2,3‐c]pyrazole‐5‐carboxylate 2 with hydrazine hydrate in good yield, and compound 2 was obtained by the reaction of 5‐chloro‐3‐methyl‐1‐phenyl‐1H‐pyrazole‐4‐carbaldehyde 1 and 2‐ethyl thioglycolate in presence of sodium alcoholate in good yield.     

Electro-oxidation and determination of antihistamine drug, cetirizine dihydrochloride at glassy carbon electrode modified with multi-walled carbon nanotubes

A multi-walled carbon nanotube (MWCNT) film-modified glassy carbon electrode (GCE) was constructed for the determination of an antihistamine drug, cetirizine dihydrochloride (CTZH) using cyclic voltammetry (CV). Owing to the unique structure and extraordinary properties of MWCNT, the MWCNT film has shown an obvious electrocatalytic activity towards oxidation of CTZH, since it facilitates the electron transfer and significantly enhances the oxidation peak current of CTZH. All experimental parameters have been optimized. Under the optimum conditions, the oxidation peak current was linearly proportional to the concentration of CTZH in the range from 5.0×10(-7) to 1.0×10(-5)M. The detection limit was 7.07×10(-8)M with 180s accumulation. Finally, the proposed sensitive and simple electrochemical method was successfully applied to CTZH determination in pharmaceutical and urine samples.     

Spectrofluorimetric Studies of the Interaction Between Quinine Sulfate and Riboflavin

The molecular interaction between quinine sulfate [QS] and riboflavin [RF] was investigated by fluorescence and UV-VIS absorption spectroscopy in aqueous solutions. The fluorescence of QS was quenched by RF. The Stern-Volmer quenching equation was successfully applied and the corresponding thermodynamic parameters enthalpy change (??H), Gibbs energy change (??G) and entropy change (??S) were calculated at different temperatures (294, 301, 307 and 314 K) according to the van??t Hoff equation. This information showed that hydrogen bonds play a major role in stabilizing the complex. The value of the critical energy transfer distance (R ₀) was found to be 46.47 Å, less than 50 Å, which proves that an efficient resonance energy transfer takes place between QS (donor) and RF (acceptor). The oxidation and reduction potentials determined from cyclic voltammetry indicated that association of QS and RF occurs in the excited state by electron transfer. The fluorescence quenching method was successfully applied for the direct determination of riboflavin (vitamin B₂) from pharmaceutical samples.     

CsF mediated rapid condensation of 1,3-cyclohexadione with aromatic aldehydes:Comparative study of conventional heating vs.ambient temperature

A mild,efficient and high yielding protocol for the synthesis of 2,2'-arylmethelene dicyclohexane-1,3-dione derivatives at room temperature and 9-aryl-l,8-dihydrooctahydroxanthene at conventional heating using cesium fluoride as a catalyst is reported.The major advantages of this reaction are excellent yield,very short reaction time and use of inexpensive catalyst.     

Multiresidue analysis of multiclass plant growth regulators in grapes by liquid chromatography/tandem mass spectrometry

A selective and rapid multiresidue analysis method is presented for simultaneous estimation of 12 plant growth regulators (PGRs), namely, auxins (indol-3-acetic acid, indol-3-butyric acid, and naphthyl acetic acid), cytokinins (kinetin, zeatin, and 6-benzyladenine), gibberellic acid (GA3), abscisic acid, and synthetic compounds, namely, forchlorfenuron, paclobutrazole, isoprothiolane, and 2,4-dichlorophenoxy acetic acid (2,4-D) in bud sprouts and grape berries at the development stages of 2-3 and 6-8 mm diameters, which are the critical phases when exogenous application of PGRs may be necessary to achieve desired grape quality and yield. The sample preparation method involved extraction of plant material with acidified methanol (50%) by homogenization for 2 min at 15000 rpm. The pH of the extract was enhanced up to 6 by adding ammonium acetate, followed by homogenization and centrifugation. The supernatant extract was cleaned by SPE on an Oasis HLB cartridge (200 mg, 6 cc). The final extract was measured directly by LC/MS/MS with electrospray ionization in positive mode, except for 2,4-D, GA3, and abscisic acid extracts, which required analysis in negative mode. Quantification by multiple reaction monitoring (MRM) was supported with full-scan mass spectrometric confirmation using "information-dependent acquisition" triggered with MRM to "enhanced product ionization" mode of the hybrid quadrupole-ion trap mass analyzer. The LOQ of the test analytes varied between 1 and 10 ng/g with associated recoveries of 80-120% and precision RSD <25% (n = 8). Significant matrix-induced signal suppression was recorded when the responses for pre- and postextraction spikes of analytes were compared; this could be resolved by using matrix-matched calibration standards. The method could successfully be applied in analyzing incurred residue samples and would, therefore, be useful in precisely deciding the necessity and dose of exogenous applications of PGRs on the basis of measured endogenous levels.