SYNTHESIS, CHARACTERIZATION AND PHARMACOLOGICAL STUDIES OF 4-ACYLPYRAZOLONE COMPLEXES OF SOME d-BLOCK ELEMENTS

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CHAPTER ONE

1.0       Introduction

Investigation on 4-acyl-3-methyl-1-phenyl-1H-pyrazol-5(4H)-one (4-acylpyrazol-5-one) and its transition metal complexes has attracted significant attention because of their applications as extractants1, antipyretic2, analgesic3, antitubercular4, antimycobacterial5, antibacterial6, antifungal7, and antineoplastic8 drugs. 4-acylpyrazol-5-one, is an enolizable ligand with strong ligating ability. These ligands are synthesized by direct acylation at C – 4 of 3-methyl-1-phenyl-1H-pyrazol (4H)-5-one (PMP) with acyl chloride or anhydrous pyridine in dioxane at reflux9. 4-acylpyrazol-5-ones are phototropic isomers forming ketoenol, diketo-, and aminodiketo tautomers10. These features of tautomerism imbues them with several coordination modes11 (O, O-donors, O, N-donors, O-donor) and easily form coordination compounds with virtually all the elements in the periodic tables. This ligating ability is more predominant with transition elements because of increased bonding orientation associated with the d-orbitals. Owing to their high extracting ability, lower pKa values (in comparison with acetylacetone, (acac), and thenoyltrifluroacetone, (HTTA), great separation power, intense colour of complex extract, and low solubility in aqueous medium, several workers have used 4-acylpyrazol-5-ones to extract metal ions12. Based on their ligating properties they are also used in the spectrophotometric determinations of several metal ions such as Fe(III)13, V(VI)14 UO22+15 Mo(IV)16, Ni(II)17, Co(II)18, Mn(II)19, V(IV)20, Cr(VI)21, Ca(II)22, Zn(II)23, Mg(II)24. 4-acylpyrazol-5-ones such as acetyl-(HPMAP), propionyl-(PMPrP), Butyryl-(HpmBuP), isobutyryl-(Iso-HPMBuP), benzoyl (HPMBP), valeroyl (HPMVP), isovaleroyl- (HPMisoVP), caproyl (HPMCP) trifluoroacetyl (HPTFP), and trichloroacetyl-(HPTCP)25 have been synthesized, spectroscopically characterized, and used in diverse applications that cut across medicine26, biology27 and pharmacology28.

Because of their thermal stability29 these functionalized ß–diketones are used as molecular precursors in chemical vapour deposition techniques and in fabrication of polymer light-emitting diodes for low-cost, full-colour, flat-panel displays30. The magnetic and electronic properties of ß-dikotonates are also used in liquid crystals display and supramolecular assemblies31. As catalysts in hydroformylation and hydroboration, 4-acylpyrazolonates are used as spectator donors32 for intermediate species in organic reactions. Investigation of coordination compounds of lanthanide ions has been done by several worker owing to their fluorescent broad applications in biochemistry33, materials science34, and medicine35. 4-acylpyrazol-5-ones with a pyrazole nucleus share structural features with some pyrazol-5-ones derivatives (metamidozole, phenazone or antipyrine, dipyrone, edaravone) that exhibit as analgesic, antipyretic and anti-inflamatory activity36. Because of its promising antipyretic and analgesic activity, these drugs are used for treating fever and flu-like infections37. Edarovone (3-methyl-1-phenyl-2-pyrazolin-5-one) which has close resemblance to 4-acyl-pyrazol-5-one is used in the treatment of brain ischemia38 and myocardial ischemia39. Also, because of pyrazole functionality, 4-acyl pyrazolone exhibit cytoxic activity against bacterial40 and fungal pathogens41 and cancer cells42.

1.2       Statement of the problem

SYNTHESIS, CHARACTERIZATION AND PHARMACOLOGICAL STUDIES OF 4-ACYLPYRAZOLONE COMPLEXES OF SOME d-BLOCK ELEMENTS