Phytochemical and bioactivity studies of Melastoma Malabathricum L. and Melastoma Imbricatum Wall

Abstract

Phytochemical and bioactivity studies of Melastoma malabathricum and M. imbricatum have been investigated. Isolation of the compounds was carried out using several chromatographic techniques. Chemical structures of isolated compounds were identified by spectroscopic methods including UV, IR, NMR (1H, 13C, DEPT, COSY, HMQC and HMBC) and MS. The n-hexane, ethyl acetate (EtOAc) and methanol (MeOH) extracts of the leaves of M. malabathricum yielded three new compounds, namely 2,5,6- trihydroxynaphtoic carbonic acid, methyl-2,5,6-trihydroxynaphtalene carbonate and flavonol glycoside derivative together with the known of auranamide, patriscabratine, a- amyrin, quercetin, quercitrin and kaempferol-3-O-(2”,6”-di-O-p-trans-coumaroyl)- glucoside. The n-hexane extract of the roots gave betulinic acid, serrat-14-en-16-one and 2-(2’-hydroxyvinyl)-1-methyl-4-propoxyphthalate. The EtOAc extract of the flowers yielded three compounds, kaempferol-3-O-ß-D-glucoside, kaempferol and naringenin. The MeOH extract of the flowers gave kaempferol-3-O-(2”,6”-di-O-p-trans-coumaroyl)- glucoside and kaempferol-3-O-ß-D-glucoside. The EtOAc extract of the fruits afforded betulinic acid, while the n-hexane extract of the stems gave a-amyrin. Phytochemical studies of the EtOAc extract of the leaves of M. imbricatum afforded quercitrin and the MeOH extract gave hyperin and kaempferol-3-O-(2”,6”-di-O-p-trans-coumaroyl)- glucoside. The EtOAc extract of the roots and fruits yielded betulinic acid. The n-hexane of the stems gave a-amyrin. The EtOAc extract of the flowers yielded kaempferol, kaempferol-3-O-ß-D-glucoside and quercitrin. Methylation and acetylation of isolated compounds gave the methyl ether and acetyl derivatives, respectively. The pure compounds and crude extracts were subjected to antimicrobial, antioxidant, antiinflammatory and cytotoxic assays. The MeOH extract of the fruits of M. malabathricum exhibited the strongest inhibition against bacteria, Bacillus subtilis, Streptococcus aureus, Pseudomonas aeruginosa and Escherichia coli with MIC values of 62.5, 62.5, 125.0 and 62.5 µg/mL, respectively, in the antimicrobial assay. The antioxidant assay was carried using FTC and DPPH (UV and ESR spectroscopic) methods. Kaempferol-3-O-(2”,6”-di- O-p-trans-coumaroyl)glucoside, kaempferol-3-O-ß-D-glucose, kaempferol, hyperin, quercetin and quercitrin showed strong activities with inhibition more than 90% in the FTC method. Quercetin was found to be the most active as radical scavenger in DPPH-UV and ESR method with IC50 of 0.69 and 0.65 µM, respectively. a-Amyrin and kaempferol-3-O- (2”,6”-di-O-p-trans-coumaroyl)glucoside demonstrated the strongest activities in the antiinflammatory assay of TPA mouse ear oedema with IC50 of 0.11 and 0.34 mM/ear, respectively. The EtOAc extract of the leaves of M. malabathricum displayed high activity with the inhibition of 94.3%. Kaempferol-3-O-(2”,6”-di-O-p-trans-coumaroyl)glucoside gave an IC50 of 5.6 µM in the PAF anti-inflammatory assay, while the MeOH extract of the leaves of M. imbricatum showed moderate activity with the inhibition of 78.0%. The cytotoxicity study was carried out using MTT assay on MCF7 cell line showed that kaempferol-3-O-(2”,6”-di-O-p-trans-coumaroyl)glucoside and naringenin were found to be active in inhibiting cell proliferation of MCF7 with IC50 of 0.28 and 1.3 µM, respectively.