Synthesis of derivatives of β-sitosterol and evaluation of their anti-bacterial activity

Antimicrobial resistance is one of a major health issue and warrants the development of new antimicrobial agents with structural diversity and novel mechanisms of action. β-Sitosterol is naturally abundant steroid in many plant families that shows moderate antibacterial activity. Hence, this study aimed to identify the importance of the functional groups present in β-sitosterol in enhancing the antibacterial activity. β-Sitosterol was isolated from the dichloromethane extract of fruit pulps of Persea americana (Yield 2.3% with respect to the crude). Isolated β-sitosterol was subjected to epoxidation, hydrogenation, and anti-Markovnikov hydration at the endocyclic olefin at C5-C6, and the acetylation at C3- hydroxyl group. The parent compound and semisynthetic derivatives were characterized using ¹H-NMR and FTIR and their antibacterial activity was determined using the micro broth dilution method with respect to the oxacillin and amoxicillin. The derivative with C6 hydroxyl of β-sitosterol was reported for the first time. The minimum inhibition concentrations of β-sitosterol, epoxide, and C6 hydroxyl compound were 512 ppm, and that of hydrogenated and acetylated compounds were above 1024 ppm. These empirical data revealed that the incorporation of oxygen heteroatom at the C5 and C6 positions while removing the double bond character at C5-C6 has not affected the antibacterial activity of β-sitosterol, however, hydrogenation and acetylation at the C3 hydroxyl group have significantly reduced the antibacterial activity compared to the β-sitosterol.