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Two short series of five membered heterocyclic 3,5-disubstituted–isoxazolines derivatives (Va–f) and 2,3,5-trisubstituted-pyrazolines derivatives (VIIa–f) were synthesized via 1,3-dipolar cycloaddition reaction of 2-(allyloxy)-4,6-dimethoxypyrimidine (III) with aromatic aldoximes (IV) which undergo oxidative–dehydrogenation with Chloramine-T to give 3,5-disubstituted–isoxazolines derivatives (Va–f) and oxidative cyclization of diphenyl hydrazones (VI) using Chloramine-T to give 2,3,5-trisubstituted-pyrazoline derivatives (VIIa–f) in good yield. The newly synthesized compounds were screened for anti-oxidant and anti-microbial activities. 2,3,5-trisubstituted-pyrazolines derivatives (VIIb–e) revealed higher antioxidant activity at 10 µg/mL while 3,5-disubstituted-isoxazolines derivatives (Va–c) and 2,3,5-trisubstituted-pyrazolines derivatives (VIIa–c) showed better anti-microbial activity at 100 µg/mL compared with standard vitamin C and ciprofloxacin, respectively. Structures of newly synthesized compounds were established on the basis of their elemental analysis and spectral IR, 1H-NMR and 13C-NMR.

In continuation of our research on thiosemicarbazones and their metal complexes as antiamoebic agents, a new series of indole-3-carboxaldehyde thiosemicarbazones (TSC) 1-7 were prepared by condensing indole-3-carboxaldehyde with cycloalkylaminothiocarbonyl hydrazines. Their palladium(II) complexes of the [Pd(TSC)Cl2] type, were synthesized upon coordination with [Pd(DMSO)2Cl2]. The chemical structures of all the compounds were established by elemental analyses, electronic, IR, (1)H NMR and (13)C NMR spectral data. The structure of the complexes was further established by thermogravimetric analysis and FAB MS. Spectroscopic data revealed that thiosemicarbazones act as bidentate ligands, making use of thione sulphur and azomethine nitrogen atom for coordination to the Pd(II) ion. Among all the compounds evaluated for antiamoebic activity using HM1:IMSS strain of Entamoeba histolytica, all palladium complexes were found to be more active than their respective ligands. Moreover, ligand 5 and complexes 1a-3a, 5a and 7a showed antiamoebic activity, at lower IC(50) doses when compared to the reference drug metronidazole with IC(50)=1.81 microM.

Several thiosemicarbazone derivatives of 5-nitrothiophene-2-carboxaldehyde were prepared by the simple process in which N 4 -thiosemicarbazone moiety was replaced by aliphatic, arylic and cyclic amine. Among these thiosemicarbazones compound 11 showed significant antiamoebic activity whereas compound 3 was more active antitrichomonal than the reference drug.

Cyclization of Mannich base with N(4)-substituted thiosemicarbazides by different aliphatic, aromatic and cyclic amines afforded a series of new 1-N-substituted cyclised pyrazoline analogues of thiosemicarbazones (PYZ-TSC) 1-10. Reaction of [Pd(DMSO)(2)Cl(2)] with pyrazoline derivatives led to new palladium(II) complexes [Pd(PYZ-TSC)Cl(2)] 1a-10a. The structures of all the compounds were characterized by spectroscopic methods. It was concluded that the pyrazoline thiosemicarbazone derivatives have two chelating arms, one attached at the 2-position of the pyrazole ring (that is, N donor) and other (S donor) linked to the thiosemicarbazone branch. The determination of antiamoebic activity of all the compounds was done using HM1:IMSS strain of Entamoeba histolytica, among all the complexes, 8a showed the most promising IC(50)=0.37 microM vs. IC(50)=1.81 microM of metronidazole, the reference drug. MTT assay showed that the compounds are non-toxic to human kidney epithelial cell line.

Various oxime ether derivatives of 2-acetylpyridine and 2-acetylfuran series have been synthesised. O-Alkylation of the oximes by various alkylaminoethyl halides gave the corresponding oxime ether derivatives. The structures of these compounds were elucidated by UV, IR, 1 H NMR, 13 C NMR spectroscopic methods and elemental analyses. All the compounds were screened in vitro against the HM1:IMSS strain of Entamoeba histolytica . Based on the 50% inhibitory concentration (IC 50 ) data of the 12 compounds evaluated, two of the 2-acetylpyridine series and two in the 2-acetylfuran series showed better IC 50 values in vitro when compared with the standard amoebicidal drug, metronidazole. Moreover, one compound showed the most promising antiamoebic activity (IC 50 = 0.5 μM vs IC 50 = 1.9 μM of metronidazole).