Isolation of three oligostilbenes from the bark of Shorea bracteolate
Shorea species is the largest subfamily of Dipterocarpaceae and are the source of resveratrol oligomers (oligostilbene), sesquiterpenes and triterpenes (Aminah et al., 2002). Shorea bracteolata Dyer – also called white meranti is locally known as „Meranti Pa'ang“ and is widely distributed in Sumatera, Peninsular Malaysia, Indonesia and Singapura. The tree is up to 50m in height and the timber is light hardwood. The study was undertaken to extract and isolate the chemical constituents from the stembark of Shorea species namely Shorea bracteolata and to elucidate the structures of the chemical constituents isolated by using modern spectroscopic methods. The stembark of S. bracteolata (4kg) was dried and cut into small pieces and ground to powdery about 1mm mesh size using grinder. The sample was extracted with acetone, filtered and evaporated in vacuo at 400oC to yield crude extract (320g). Diethyl ether was added to crude extract to remove the tannin. The tannin free crude extract was fractionated using vacuum liquid chromatography (VLC) to give six fractions. Fraction 2 was subjected to radial chromatography 1 [Hex:EtOAc (5:5) ] and 2 [ CHCl3:MeOH (9.5:0.5 ] to yield ε-viniferin (1) (Muhtadi et al., 2005) and α-viniferin (2) (Sutopo, 2009). Double purification of fraction 5 using radial chromatography [EtOAc:MeOH (9:1)] and [CHCl3: Acetone:MeOH (7:2:1)] afforded hopeaphenol (3) (Guebailia et al., 2006). The structure of the isolated compounds was determined based on analysis of spectroscopic data, including NMR, UV, IR and comparison with previous reported studies.
Acknowledgement: The authors would like to thank Faculty of Applied Sciences, Universiti Teknologi MARA, Malaysia for financing this research project. The scholarship of one of the authors was financed by UiTM Fellowship.
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Muhtadi HEH et al. (2005) J. Matematika dan Sains, 10(4): 137–143.
Sutopo H (2009) Modern Applied Science 3(4): 45–51.