Secondary Metabolites from Garcinia dryobalanoides and their Anti-bacterial Activity

Nur Fazlin Zafirah, Zaine (2024) Secondary Metabolites from Garcinia dryobalanoides and their Anti-bacterial Activity. Masters thesis, Universiti Malaysia Sarawak.

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Abstract

Garcinia was discovered to have excellent sources of bioactive compounds with therapeutic potential and hence received significant attention due to its potential for medicinal applications. This study investigates Garcinia species' secondary metabolites and their anti-bacterial activity, specifically Garcinia dryobalanoides. Different chromatographic methods were used to isolate and purify the pure compounds. Along with that, structural modification of the major compound was successfully synthesized via Williamson etherification. The structural elucidations of these isolated and synthesized compounds were achieved through FT-IR, UV-Vis, LC-MS, 1D, and 2D-NMR. Anti-bacterial tests were conducted against various bacterial strains, including Gram-positive bacteria (Lactiplantibacillus plantarum) and Gram-negative bacteria (Enterobacter cloacae, Pseudomonas aeruginosa, and Serratia marcescens). Six compounds (76, 2, 77, 78, 79 and 59) were successfully isolated and five rubraxanthone derivatives (80 – 84) were successfully synthesized. Astonishingly, compound 76 was the first naturally occurring benzophenone isolated from the Garcinia genus. The anti-bacterial evaluation on crude extract, isolated, and synthesized compounds against tested bacteria demonstrated moderate to excellent activities outlining anti-bacterial potential. Structure-activity relationships (SAR) study demonstrated that xanthones bearing prenyl and hydroxy groups exhibit excellent bacterial inhibition. However, adding an alkyl chain to the hydroxyl group reduced this effect, possibly due to steric hindrance. This study highlights Garcinia species as a promising source of natural anti-bacterial and further investigation is needed.

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