ISOLATION, PRENYLATION, AND ANTIOXIDANT ASSAY OF STILBENOIDS FROM HEARTWOOD OF GNETUM GNEMON

• Main Author: Musyarrofah, Lailatul
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/65271
• Institution: Institut Teknologi Bandung

Gnetum gnemon, which belongs to the Gnetaceae family and locally known as melinjo, is widely cultivated in Indonesia. The seeds, fruit peel, and leaves of melinjo have all been consumed as edible part of this plant. In Banten, G. gnemon seeds have been processed as a food product named emping, which is one of the livelihood sources. According to the literature, this species has been used as a traditional medicine in arthritis, bronchitis, and asthma treatments. The efficacy of plants as medicines is related to their secondary metabolites. It has been reported in several studies that the main compounds of G. gnemon are a group of stilbenoids with their dimers and trimers. These compounds are known to have various bioactivities such as antioxidant, antimicrobial, and inhibition of angiogenesis, tyrosine activity, and melanin synthesis. Thus far, studies on secondary metabolites from Indonesian G. gnemon have been carried out on the seeds, fruit peel, stem bark, leaves, and roots. However, the study on secondary metabolites in the heartwood of G. gnemon is still limited. Therefore, in this research, isolation of secondary metabolites (especially stilbenoid compounds) in the heartwood of G. gnemon collected from Desa Melati, Kabupaten Serang, Banten, was conducted. In addition, the prenylation reaction was also carried out on the major stilbenoid derivatives isolated from the heartwood of this species to study its structure and activity. Isolation of secondary metabolites from the heartwood powder of G. gnemon was carried out in several steps, including maceration with acetone solvent, followed by separation and purification of acetone extract using Vacuum Liquid Chromatography (VLC) and Gravitational Column Chromatography (GCC). The structures of the isolated compounds and prenylated products were determined based on spectroscopic data, including 1D-NMR (1H-NMR and 13C NMR) and 2D-NMR (HSQC and HMBC). The prenylation of the major stilbenoid derivatives was carried out using 3,3-diallylbromide under base conditions. The preliminary antioxidant assay on the isolated compounds and prenylated products was carried out using the DPPH method. In this research, the four secondary metabolites have been isolated, including three stilbenoid derivatives, namely trans-resveratrol, piceatannol, and isorhapontigenin, with a simple phenolic, vanillin. Vanillin and piceatannol were first reported from G. gnemon, while trans-resveratrol and isorhapontigenin were previously reported isolated from the stem bark and fruit peel of G. gnemon. Isorhapontigenin is the major compound in the heartwood of G. gnemon (yield 0.035%, 344.5 mg from 1 kg of dried wood). Four isorhapontigenin derivatives, LMP1-4, were obtained from the prenylation. LMP1 (yield 28.4%) and LMP3 (yield 6.7%) were identified as monoprenylated isorhapontigenins, while LMP2 (yield 8.1%) and LMP4 (yield 5.2%) were identified as diprenylated isorhapontigenins. Piceatannol showed the highest inhibition percentage (81%) of the antioxidant activity assay (40 ?M in 10 minutes inhibition duration), while isorhapontigenin and trans-resveratrol showed similar inhibition percentage (50% and 47%). As for isorhapontigenin derivatives, the monopyrenylated isorhapontigenin (LMP3) increased the percentage inhibition of isorhapontigenin by 1.4 times from 50% to 69%. This result suggests that the certain prenylation at the C11 oxygen and the free hydroxyl at the C4 are the significant factors for antioxidant activity of isorhapontigenin.