Chemotaxonomy and Antibacterial Activity of the Extracts and Chemical Constituents of Psychotria succulenta Hiern. (Rubiaceae)

Abstract

The use of natural products for medicinal purposes is becoming more and more common nowadays, as evidenced by the presence in plants of secondary metabolites with different potentials such as antioxidant and antibacterial properties. We evaluated in this work the antimicrobial activities of the extracts and some isolated compounds from the seeds of Psychotria succulenta Hiern. (Rubiaceae), a Cameroonian medicinal plant traditionally used to cure microbial infections. The ethanol extract was prepared by maceration and extracted with ethyl acetate and n-butanol. The EtOAc ( m = 168 g ) and n-BuOH ( m = 20 g ) extracts were further fractionated by silica gel column chromatography to isolation of compounds. Their structures were elucidated by spectroscopic analysis and by comparison with published data. The antibacterial activity of extracts and compounds was assessed by evaluating the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against pathogenic bacteria. Thirteen compounds including four alkaloids (veprisine (1), naucleofficine III (2), vepridimerine B (3), and vepridimerine C (4)), three triterpenes (barbinervic acid (5), 3-O-α-L-rhamnopyranosyl quinovic acid (6), and oleanolic acid (7)), one steroid (β-sitosterol-3-O-β-D-glucopyranoside (8)), four phenolic compounds (scopoletin (9), gallic acid (10), quercetin-3-O-β-D-glucopyranoside (11), and kaempferol 3-O-α-L-rhamnopyranoside-7-O-α-L-rhamnopyranoside (12)), and one iridoid (borreriagenin (13)) were isolated from the EtOAc and n-BuOH extracts. These compounds were identified by 1D and 2D NMR combined analysis as well as by melting point comparison. The EtOH, EtOAc, and n-BuOH extracts exhibited significant antibacterial activities ( MIC = 32 ‐ 128 μ g / mL ; MBC = 64 ‐ 256 μ g / mL ) against Staphylococcus aureus (Gram-positive bacterium), Pseudomonas aeruginosa, Escherichia coli, and Klebsiella pneumonia (Gram-negative bacteria). Among the isolated compounds, scopoletin (9) showed a moderate activity against Klebsiella pneumoniae with MIC and MBC values of 16 μg/mL and 32 μg/mL, respectively. It appears that, chemotaxonomically, some of the isolated compounds have already been obtained from the genus Psychotria but to the best of our knowledge, this is the first report on the phytochemical investigation of P. succulenta. Although many other studies need to be achieved, our results support the use of P. succulenta in traditional medicine to cure infectious diseases particularly those caused by the tested bacteria.

Chemical Constituents of Macaranga occidentalis, Antimicrobial and Chemophenetic Studies

“…This suggests that the plant contains several active principles with different polarities, as shown by the nature of the isolates. Indeed, the antibacterial activity of medicinal plants is correlated with their chemical composition [3]. The n-BuOH fraction was the most active against Escherichia coli ATCC 25922, but all of the isolated compounds from this fraction presented weak or no activity against the selected strains, which could be due to the synergetic effect of the different constituents of this fraction.…”

“…The high rate of bacterial resistance to available antibiotics is alarming and makes the treatment of even simple bacterial infections difficult [2]. This resistance could be due to the capacity of Gram-positive or Gram-negative bacteria to acquire resistance mechanisms to face environmental aggression such as competing bacteria, the natural environment, host defense, or antibiotics, either by modification of the anti-infective active sites or by the production of degradative enzymes [3]. This concern requires a continuous search for new and efficient lead antibacterial agents to fight against multiresistant microbial agents and to limit undesirable side effects.…”