Chemical constituents and antibacterial activity of Melastoma malabathricum L.

Abstract

The aqueous methanolic extracts of Melastoma malabathricum L. exhibited antibacterial activity when assayed against seven microorganisms by the agar diffusion method. Solvent fractionation afforded active chloroform and ethyl acetate fractions from the leaves and the flowers, respectively. A phytochemical study resulted in the identification of ursolic acid (1), 2α-hydroxyursolic acid (2), asiatic acid (3), β-sitosterol 3-O-β-D-glucopyranoside (4) and the glycolipid glycerol 1,2-dilinolenyl-3-O-β-D-galactopyanoside (5) from the chloroform fraction. Kaempferol (6), kaempferol 3-O-α-L-rhamnopyranoside (7), kaempferol 3-O-β-D-glucopyranoside (8), kaempferol 3-O-β-D-galactopyranoside (9), kaempferol 3-O-(2″,6″-di-O-E-p-coumaryl)-β-D-galactopyranoside (10), quercetin (11) and ellagic acid (12) were found in the ethyl acetate fraction. The structures of these compounds were determined by chemical and spectral analyses. Compounds 1-4, the flavonols (6 and 11) and ellagic acid (12) were found to be active against some of the tested microorganisms, while the kaempferol 3-O-glycosides (7-9) did not show any activity, indicating the role of the free 3-OH for antibacterial activity. Addition of p-coumaryl groups results in mild activity for 10 against Staphylococcus aureus and Bacillus cereus. Compounds 2-5, 7 and 9-12 are reported for the first time from M. malabathricum. Compound 10 is rare, being reported only once before from a plant, without assignment of the double bond geometry in the p-coumaryl moiety.

Antibacterial effects and action modes of asiatic acid

“…The antibacterial activity of asiatic acid against E. coli, B. subtilis and S. sonnei has been reported before [13]. The results of our present study extend the inhibitory effects of this agent toward other Gram-negative and Gram-positive foodborne bacterial pathogens including S. Typhimurium DT104, P. aeruginosa, L. monocytogenes, S. aureus, E. faecalis, and B. cereus.…”

“…), basil (Ocimum basilicum), and brown mustard (Brassica juncea) [10,11]. It has been reported that this compound exhibits inhibitory effects against S. aureus, B. cereus, E. coli, B. subtilis, and Shigella sonnei, as determined by agar diffusion methods [12,13]. Garo et al indicated that asiatic acid could enhance the susceptibility of P. aeruginosa biofilms to tobramycin [14].…”

Antibacterial Activities of Flavonoids: Structure-Activity Relationship and Mechanism

“…Flavonols have been reported to be active agents against both gramnegative and gram-positive microorganisms, but the flavonols with only hydroxyl or methoxyl substitutions generally show activity that is rather weaker than common antibiotics [48][49][50]. For example, kaempferol showed activity against S. aureus and E. coli, and the MIC values was respectively 63 and 16 g mL -1 , while those values of gentamicin (antibiotic) was only 0.2 and 0.8 g mL-1, correspondingly [51].…”

Growth inhibition and antioxidative response of wood decay fungi exposed to plant extracts ofCaseariaspecies

“…; Sova ; Wong et al . ). A wood preservative formulation based on cinnamic acid at 15% protected wood samples against Trametes versicolor for 3 months (Kartal et al .…”