Antimicrobial and acetylcholinesterase inhibitory activities of Buddleja salviifolia (L.) Lam. leaf extracts and isolated compounds

Ethnopharmacological relevance

Buddleja salviifolia leaves are used for the treatment of eye infections and neurodegenerative conditions by various tribes in South Africa.

Aim of study

This study was designed to isolate the phenolic constituents from the leaf extracts of Buddleja salviifolia and evaluate their antimicrobial and acetylcholinesterase (AChE) activities.

Material and methods

Three phenolic compounds were isolated from the ethyl acetate fraction of a 20% aqueous methanol leaf extract of Buddleja salviifolia using Sephadex LH-20 and silica gel columns. Structure elucidation of the isolated compounds was carried out using spectroscopic techniques: mass spectrometry (ESI-TOF-MS) and NMR (1D and 2D). The extracts and isolated compounds were evaluated for antimicrobial and acetylcholinesterase activities using the microdilution technique. The bacteria used for the antimicrobial assays were Gram-positive Bacillus subtilis and Staphylococcus aureus and Gram-negative Escherichia coli and Klebsiella pneumoniae.

Results

The isolated compounds were characterized as: 4′-hydroxyphenyl ethyl vanillate (1) a new natural product, acteoside (2) and quercetin (3). The crude extract, fractions and the isolated compounds from the leaves of the plant exhibited a broad spectrum of antibacterial activity. The EtOAc fraction exhibited good activity against Bacillus subtilis and Staphylococcus aureus with MIC values ranging from 780.0 to 390.0 µg/mL. Isolated compound 2 exhibited good activity against Staphylococcus aureus with an MIC value of 62.5 µg/mL. The hexane and DCM fractions of leaves showed the best activity against Candida albicans with MIC and MFC values of 390.0 µg/mL. In the AChE inhibitory test, among the tested extracts, the hexane fraction was the most potent with an IC₅₀ value of 107.4 µg/mL, whereas for the isolated compounds, it was compound (3) (quercetin) with an IC₅₀ value of 66.8 µg/mL.

Conclusions

Activities demonstrated by the extracts and isolated compounds support the ethnopharmacological use of Buddleja salviifolia against eye infections and neurodegenerative diseases.