Antimicrobial activities of extract, fractions and compounds from the medicinal plant Helichrysum odoratissimun (L.) Sweet (Asteraceae)

The use of plants in the treatment of various diseases is a practice known since ancient times, and even nowadays, a number of plant products are traditionally used as medicines. Many modern medicines are frequently based on plant biologically active compounds. The aim of this study was to evaluate the antimicrobial activity of extract, fractions and compounds isolated from Helichrysum odoratissimun (Asteraceae) against some bacteria and fungi using the broth microdilution method. The in vitro antibacterial and antifungal activities of the EtOH (ethanol) extract and the n-BuOH (n-butanol) and EtOAc (ethyl acetate) fractions as well as compounds 1-8 were evaluated. The EtOAc fraction showed the most potent activity against Pseudomonas aeruginosa (ATCC74117) and Candida albicans (ATCC 9028) with minimum inhibitory concentration (MIC) values at 16 µg/mL and 32 µg/mL, respectively. Otherwise, the n-BuOH fraction showed activity against Candida albicans (ATCC 9028) with a MIC value of 64 µg/mL. Based on these results, the EtOAc and n-BuOH fractions were purified using varying chromatographic methods to afford 5,8-dihydroxy-3,6,7-trimethoxyflavone (1), 5,4´-dihydroxy-7-methoxyflavanone (2), methylinositol (3), quercetin (4), quercetin-3-methoxy-7-O-β-D-glucopyranoside (5), 3-hydroxydihydrobenzofurane (6), 4,5-di-p-trans-coumaroyl quinic acid (7), kaempferol (8), β-sitosterol- 3-O-β-D-glucopyranoside (9), and oleanolic acid (10), Their structures were established using extensive spectroscopic and spectrometric analysis as well as comparison with published data. Among the isolated compounds, 5,8-dihydroxy-3,6,7-trimethoxyflavone, 5,4´-dihydroxy-7-methoxyflavanone and quercetin showed moderated activity against Candida albicans with MIC values of 64 µg/mL, 64 µg/mL and 32 µg/mL, respectively. These results are in agreement with the use of H. odoratissimun in traditional medicine against infectious diseases. To the best of our knowledge, this is the first report on the isolation of compounds 1-10 from this medicinal plant.