Phytochemicals and bioactivities of Garcinia prainiana King and G. hombroniana Pierre

Abstract

Phytochemical and bioactivity investigations of two Garcinia species, namely Garcinia prainiana King and G. hombroniana Pierre have been carried out. The leaves and barks of G. prainiana and the roots of G. hombroniana were extracted using n-hexane, dichloromethane and methanol, consecutively. Isolation and purification of the crude extracts carried out using several chromatographic techniques have led to the identification of seventeen compounds. The structures of the isolated compounds were elucidated by spectroscopic methods such as UV, IR, 1D (1H, 13C, DEPT) and 2D (COSY, HMQC, HMBC) NMR and MS. Purification of the leaves and barks extracts of G. prainiana afforded eleven known compounds. Six triterpenes identified as squalene, friedelin, lupeol, methyl putranjivate, eupha-5,22-diene-3β-ol and eupha-5,22-diene-3β-acetate were isolated from the n-hexane extracts of leaves and barks of G. prainiana while five biflavonoids characterized as morelloflavone, O-methylfukugetin, volkensiflavone, amentoflavone and 4'"-methylamentoflavone were obtained from the methanol extract of barks of G. prainiana. Purification of the roots extract of G. hombroniana yielded two new compounds, 1,3,7-trihydroxy-4-(1,1-dimethylprop-2-enyl)-8-methoxyxanthone and 3,3',4",5',5",6-hexahydroxybenzophenone together with four known compounds, garceduxanthone, cheffouxanthone, norathyriol and 2,3ʹ,4,5ʹ-tetrahydroxy-6-methoxybenzophenone. Total phenolic content, total antioxidant, antibacterial, antityrosinase and toxicity studies were carried out on the crude extracts and selected compounds. Measurement of the total phenolic content using Folin-Ciocalteau reagent indicated that the crude methanol extract of the barks of G. prainiana had the highest value of gallic acid and (±)-catechin equivalents. The crude methanol extract also showed the highest value of ascorbic acid and butylated hydroxytoluene equivalents on forming the phosphomolybdenum complex in the total antioxidant assay. The antioxidant assays on 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical showed that the crude methanol extract of barks of G. prainiana had the highest radical scavenging activity. Morelloflavone revealed a strong free radical scavenging activity with IC50 value 15.7 μg/mL. The antibacterial assay was carried out using disc diffusion method, followed by minimum inhibition concentration (MIC) determinations. The crude methanol extract of the barks of G. prainiana displayed weak antibacterial activity against Gram-negative bacteria Pseudomonas aeruginosa and Gram-positive bacteria Bacillus subtilis. The selected compound, morelloflavone, showed moderate antibacterial activity against B. subtilis and P. aeruginosa with MIC value of 450 μg/mL. The cytotoxic activities of the isolated compounds were evaluated using the MTT assay against H1299 and A549 lung cancer cells. The results showed that eupha-5,22-diene-3β-acetate had strong cytotoxity activity against H1299 and A549 cell lines with IC50 values of 18.0 and 36.3 μg/mL, respectively while squalene gave IC50 values of 23.2 μg/mL (H1299) and 74.8 μg/mL (A549). Meanwhile, the screening for antityrosinase activity using the mushroom tyrosinase enzyme assay for all crude extracts and isolated compounds showed that the percentage of tyrosinase inhibition at a concentration of 100 μg/mL were higher than 50%.