Structure Activity Relationship Studies of Synthesised Schiff Bases and Mannich Bases of Substituted 5-Methyl-1, 2-Dihydro-3H-Pyrazol-3-One Derivatives Having Variable Electronegative Atoms for Antioxidant Screening

The proposed project has been designed for structure activity relationship by the Schiff base and Mannich base of substituted 5-methyl-1,2-dihydro-3Hpyrazol- 3-one derivatives for antioxidant screening.

The scheme for synthesis has been designed to synthesise 5-methyl-1,2- dihydro-3H-pyrazol-3-one molecule is done by reacting ethyl acetoacetate with hydrazine and then by benzoylation in basic medium produced 1,2- dibenzoyl derivative of the heterocyclic ring. Further condensation with hydrazine with this heterocyclic ring produced Schiff base at three positions where free ketone group is present. This tri-Schiff base has been condensed with various ketone compounds to produce Schiff base of R1/R2 at three positions as well as the same tri-Schiff bas on condensation with benzaldehyde with urea/thiourea/guanidine produced Mannich bases ath three positions for X=O/S/NH. The synthesised compounds have been characterized by N% and UV, IR, NMR and Mass Spectra. The antioxidant screening is based on the iodine spot activity of synthesised compounds by zone diameter calculation. It has been observed that in Mannich bases derivatives guanidine derivative (Compound-7) showed maximum antioxidant activity. The profile for the antioxidant activity is: Compound- 7(X=NH)>Compound-6(X=S)>Compound-5(X=O). It happens due to the electronegativity: NH=3.1+2.2=5.3; S=2.4; O=3.5. Here "N" has one lone pair of electrons whereas "O" and "S" has two lone pair of electrons but the electronegativity of "NH" is maximum in comparison to "S" and "O" which both have two lone pair of electrons but the electronegativity of "S" is lower that "O" so the antioxidant profile showed a very good satisfactory result. In case of Schiff bases the butanone derivative (Compound-4) showed maximum antioxidant activity. The profile for the antioxidant activity is: Compound-4(R₁=CH₃,R₂=C₂H₅)>Compound-1(R₁=R₂=CH₃)>Compound- 3(R₁=R₂=C₆H₅)>Compound-2(R₁=CH₃,R₂=C₆H₅). It happens due to the presence of CH₃+C₂H₅=3 carbons in alipahtic chain in case of Compound- 4(R₁=CH₃,R₂=C₂H₅) but in case of Compound-1(R₁=R₂=CH₃), here CH₃+CH₃=2 carbons in aliphatic chain, in Compound-3(R₁=R₂=C₆H₅), here C₆H₅+C₆H₅=12 carbons in aromatic ring and in Compound- 2(R₁=CH₃,R₂=C₆H₅), here CH₃+C₆H₅=7 carbons in alipahtic and aromatic ring. Compound-4(R₁=CH₃,R₂=C₂H₅) of Schiff base is more active than Mannich base of Compound-7(X=NH) in antioxidant activity.