Synthesis and Characterisation of Halogenated Vanillin Derivatives as Potential Antibacterial Agents

Mohamad Azmeer, Hissam (2023) Synthesis and Characterisation of Halogenated Vanillin Derivatives as Potential Antibacterial Agents. Masters thesis, Universiti Malaysia Sarawak.

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Abstract

The escalating issue of antimicrobial resistance has become a pressing global challenge and poses a significant threat to public health. Thus, new potent drugs derived from natural product are in demand in the pharmaceutical sector as it offers a wide range of chemical structures and diverse bioactive compounds. However, the extraction of secondary metabolites from natural resources are labour-intensive, time-consuming and frequently inefficient due to the mismatch between the active group and the target receptor. Chemical modification of a lead compound derived from natural resources such as vanillin has garnered increasing attention for pharmacological purposes. In this study, three different series of novel vanillin derivatives namely halogenated vanillin azo derivatives (43a-h) were successfully synthesised via diazo coupling reaction, while halogenated vanillin Schiff base derivatives were prepared via nucleophilic substitution reaction (44a-h). The hybrid molecules of vanillin azo-Schiff base derivatives bearing halogens (Br, Cl, F) (45a-h) were prepared from the reaction of 43a-h with aniline to give significant yields of 67-83% via microwave irradiation method compared to the conventional heating (38-53%). The antibacterial assay of all synthesised compounds at a concentration of 100 ppm was evaluated employing Kirby-Bauer disc diffusion assays against Escherichia coli (ATCC 25922) and Staphylococcus aureus (S48/81). All target compounds were active against both bacterial strains in comparison to the parent vanillin. Compounds 43a-h and 44a-h were active against S. aureus with inhibition zones of 7-10 mm and 8-13 mm, respectively, but less active against E. coli with inhibition zones of 7-9 mm and 7-8 mm, respectively. Notably, compounds 45a-h demonstrated good antibacterial activity (8-11mm) against both bacterial strains in comparison to the standard drug ampicillin (11 mm). Among the halogenated vanillin azo-Schiff base derivatives, compound bearing fluorine at meta position (45b) demonstrated excellent antibacterial efficacy against E. coli and S. aureus with both inhibition zones of 11 mm respectively, comparable to standard drug ampicillin. The successful synthesis of these hybrid vanillin azo-Schiff base derivatives implies their potential utility in drug design that will aid in the development of new, potent antibacterial drugs with excellent properties.

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