SYNTHESIS OF NEW ANTIBIOTICS RELATED TO 3 AND 5-AMINO-β-RESORCYLIC ACID ENTITIES AND THEIR BIOACTIVITY SCREENING

Abstract

In an attempt to synthesize new antibiotics related to 3 and 5-amino-β- resorcylic acid entities a number of new amide derivatives of 5-amino-β-resorcylic acid were synthesized (15-19) in the course of current study. To study the influence of electron density on stabilization of Ag metal, the synthesized amides were tested for the synthesis of silver nanoparticles (Ag NPs). It was found that as electron density of ligand increases, lesser amount of it is required for capping Ag metal Ag NPs capped with ligand 14 and ligand 19 exhibited higher antibacterial activity than ligand 14 and 19 against Erwinia carotovora pv. carotovora. Ag NPs functionalized with ligand 13, 16 and ligand 19 showed greater inhibitions in growth of Alternaria solani than their ligands. The effect of electron density on growth of inhibition of Erwinia carotovora was also tested. It was established that as electron donating character inreases from ligand 16, 17 and 19, growth of inhibition (%) reduces. However antibacterial activity of these ligand enhances after formation of Ag NPs. So, it was concluded that electron density had a robust impact on antibacterial activity of Ag NPs. A sulfonic acid substituted benzoic acid derivative (Potassium 4- carboxybenzenesulfonate 20) was synthesized and used for synthesis of Ag NPs. Ligand 20 and its Ag NPs are more potent than standard drug (Streptomycin) at 150 and 200 ppm against Erwinia carotovora. Ag NPs stabilize with ligand 20 showed greater antibacterial activity than ligand 20 against Alternaria solani. A number of new strategies were tried for synthesis of 3-amino-β-resorcylic acid, but we failed to synthesize this entity. A novel terathiacyclophane macrocycle 25 was synthesized from 2,4- dihydroxybenzoic acid 1 and used for the formation of Ag NPs. Ag NPs capped with ligand 25 showed excellent antibacterial activity against Erwinia carotovora pv. carotovora than ligand 25 which was completely inactive. However, brine shrimp lethality bioassay test revealed that at 200 ppm, macrocycle 25 and standard drug (Etoposide) showed similar cytotoxic activity against the experimental shrimps. 2,4-dihydroxybenzene carbodithioic acid 28 derivative of 2,4- dihydroxybenzoic 1 acid was also prepared. Biocide 28 Au NPs were synthesized in one pot without using reducing agent. The amount of ligand 28 conjugated to the Au iiiNPs was found to be 7 % by weight, our results indicated that conjugation to the Au NPs boosts the biocidal activity of ligand 28 about 14 times. It has been verified that the structure of Ag and Au nanoparticle core can be determined from MALDI-TOF MS analysis (chapter 4 and 6). Both TEM characterization and MALDI-TOF spectrum analysis of Ag NPs stabilize with ligand 14 and Au NPs capped with ligand 28 indicated the formation of polydispersed nanoparticles. A chemical ionization mechanism is proposed for protonation of the three labile protons of the ligand in nanosilver and nanogold because all the fragments of mass spectrum yielded triply charged specie. To ascertain the potential for in vivo applications, the stability of all synthesized nanoparticles was investigated as a function of temperature, pH and salt concentration. The suspensions were found to be stable for several days at temperatures of up to 100 ̊ C, a pH range of 2-13 and salt concentrations (NaCl) up to 4 mol/L. 5-Amino-β-resorcylic acid hydrochloride dihydrate 13 was used as a chemosensor for quantitative estimation of Sb 3+ . On the basis of three times the standard deviation of the blank (3σ), detection limit was found to be 30 μM. The Sb(III) obeyed Beer’s law from 1-20 equivalents with a linear regression equation of I = 325.2 + 33.78 C with R 2 = 0.967.