{'fraction_non_alphanumeric': 0.04308828702075273, 'fraction_numerical': 0.02321491382342596, 'mean_word_length': 5.0052798310454065, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
ANTI-RADICAL ACTIVITIES OF XANTHONES AND FLAVONOIDS FROM GARCINIA SCHOMBURGKIANA

Objective: The present study aimed to isolate and identify the phytochemical constituents of Garcinia schomburgkiana branches and evaluate the antioxidant activity of the compounds. Methods: The chromatographic and spectroscopic (UV, IR, NMR and MS) techniques were used for the isolation and elucidation of the compounds, respectively. The antioxidant activity of the isolated compounds was examined through DPPH, ABTS, nitric oxide and hydroxyl radical scavenging assay. Results: The (-)-5,7,3′,5′-tetrahydroxyflavanone (1), which was firstly found in the Garcinia species, together with kaempferol (2), (-)dihydrokaempferol (3), euxanthone (4), gentisein (5) and norathyriol (6) were isolated from G. schomburgkiana. Among the isolated compounds, compound 1 and 6 exhibited the highest potential for anti-radical activities. Conclusion: Compound 1 could be used as the chemotaxonomic marker of G. schomburgkiana. The branches of G. schomburgkiana could be the alternative source of the antioxidants. The possible inhibitory mechanisms were proposed through the action of electron transfer, chelation, and nitrosylation.


INTRODUCTION
In Thailand, there are 29 species of the genus Garcinia, belonging to the family Clusiaceae. A variety of phytochemicals, xanthone, flavonoid, phloroglucinol and triterpene, as well as pharmacological activities, anti-oxidant, anti-inflammatory, antimicrobial and anticancer, have been being studied [1]. Garcinia schomburgkiana, locally named Ma-dan, is commonly found in South-East Asia. Its fruits, leaves and roots have been traditionally used as a cough and diabetes treatment [2]. The wood, stem and bark of G. schomburgkiana were studied on the chemical constituents and their cytotoxicity. They revealed the presence of xanthones, benzophenones, biphenyls and bioflavonoids [3][4][5]. Some flavonoids from the genus Garcinia such as morelloflavone and fukugeside have been used as the chemotaxonomic markers [6]. Prior to this investigation, the branch of G. schomburgkiana, however, has never been reported on the anti-radical activity. Hence, the present study was undertaken to examine the anti-radical activity and phytochemical constituents of the branch of G. schomburgkiana.

Plant material
In this study, branches of G. schomburgkiana Pierre. were collected from Yan Ta Khao district, Trang Province, Thailand, in October 2013. A voucher specimen (GS-001WU) is deposited at the Research Unit of Natural Product Utilization, Walailak University, Nakhon Si Thammarat, Thailand.

Extraction and isolation
Powdered, dried branches of G. schomburgkiana (17.5 kg) were macerated twice with acetone (32 l) for 5 d at room temperature. The filtrate was combined and the solvent evaporation was carried out under a vacuum to give the crude extract (400 g). The crude extract (100 g) was then subjected to a silica gel column chromatography eluted with gradient CH2Cl2: MeOH to yield 12 fractions (A-L).

Antiradical activity assay
The diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay The DPPH radical scavenging was determined using the method described by Zongo et al. and Gogoi et al. [7,8]. Ascorbic acid was used as the standard. Briefly, the 100 µl of the extracts or standard solution in DMSO (various concentrations: µg/ml) and 100 µl of the DPPH-radical (100 µg/ml in methanol) were mixed. After 15 min at room temperature in the dark, the absorbance of the mixture was measured at 517 nm. The data were expressed as the half maximal radical scavenging concentration (SC50). The equation 1 below was used to calculate the percentage of DPPHradical scavenging.
Where,Asample: The absorbance of the extracts or standards mixed with DPPH Acontrol: The absorbance of the DMSO mixed with DPPH

The 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) cation radical scavenging assay
The ABTS cation radical scavenging was performed according to Re et al. [9] with slight modification. Trolox was used as the standard. Briefly, the ABTS radical cation was produced by the reaction of 7 mmol ABTS solution in DI water with 2.45 mmol K2S2O8 in DI water. After the mixture was stored in the dark at 4 °C for 12-16 h, the absorbance of the mixture (ABTS cation radical) was adjusted to 0.70±0.02 at 734 nm by diluting with DI water. The 20 μl of the extracts or standard solution in DMSO (various concentrations: µg/ml) was mixed with 180 µl of ABTS cation radical. After 3 min at room temperature, the absorbance was measured at 734 nm. The data were expressed as the half maximal radical scavenging concentration (SC50). To calculate the percentage of ABTS cation radical scavenging, equation 2 below was used.

The nitric oxide scavenging assay
This nitric oxide scavenging activity was estimated according to the method of Harput et al., . Vitamin C and quercetin were used as the standards. Briefly, 50 µl of the extracts with varying concentrations (µg/ml) in DMSO and 50 µl of 10 mmol sodium nitroprusside in phosphate buffer saline (PBS), pH 7.4, were mixed. After incubation at room temperature for 150 min under the light condition, 100 µl of Griess reagent (1 % sulfanilamide and 0.1 % N-(1-Naphthyl) ethylenediamine dihydrochloride in 2.5 % H3PO4) was added. After 10 min at room temperature, the absorbance was recorded at 577 nm. The percentage of nitric oxide scavenging was calculated through equation 3 below. The data were represented as the half maximal radical scavenging concentration (SC50).

Statistical analysis
All analyses were tested in triplicate and represented as the means±standard deviation (SD).