Antimicrobial secondary metabolites from the medicinal plant Crinum glaucum A. Chev. (Amaryllidaceae)

Medicinal plants are known as sources of potential antibacterial compounds including alkaloids. The aim of the present study was to evaluate the antibacterial activities of the extract, fractions, and some secondary metabolites isolated from the leaves of Crinum glaucum A. Chev. (Amaryllidaceae). The antibacterial activities were performed with the ethanol (EtOH) extract, as well as with ethyl acetate (EtOAc) and n-butanol (n-BuOH) fractions. Repeated column chromatography of the fractions led to the isolation of several compounds and their structures were elucidated mainly by means of extensive spectroscopic analysis [(one-dimensional (1D) and two-dimensional (2D) nuclear magnetic resonance (NMR), mass spectrometry)] and the comparison with published data. This includes eleven alkaloids: (3S)-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid (1), lycorine (2), ungeremine (3), ambelline (4), macronine (5), 5,6-dihydrobicolorine (6), trisphaeridine (7), hippadine (8), adenosine (9), arolycoricidine (10), pratorimine (11); two steroids: beta-sitosterol (12), beta-sitosterol-3-O-beta-D glucopyranoside (14) and one triterpene: oleanolic acid (13). Apart from lycorine (2), all these secondary metabolites are isolated from C. glaucum for the first time. The in vitro antibacterial activity of the EtOH extract, and the n-BuOH and EtOAc fractions as well as compounds 2, 3, 6 and 9 against pathogenic bacteria was performed. All extracts and fractions showed varying levels of antibacterial properties against at least one of the bacteria strains tested. The n-BuOH fraction was the most active extract with the lowest minimal inhibitory concentration (MIC) value of 64 mu g/mL against Enterococcus faecalis. For pure compounds, the best MIC (8 mu g/mL) was obtained with ungeremine (3) against Enterococcus faecalis and Pseudomonas aeruginosa. Our results show the antimicrobial potential of C. glaucum and scientifically validate its uses in traditional medicine against infectious diseases including cough and sexually transmitted infections. Ungeremine seems to be the antimicrobial active ingredient of this medicinal plant. (C) 2020 SAAB. Published by Elsevier B.V. All rights reserved.