Bioassay Guided Isolation Of Antitermite Compounds From The Bark Of Rhizophora Apiculata

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Date
2009-11
Authors
Kong Nein, Hing
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Publisher
Universiti Sains Malaysia
Abstract
The powdered bark of Rhizophora apiculata was initially extracted with petroleum ether (PE) and methanol. The aqueous methanol extract was re-extracted into chloroform (CE), ethyl acetate (EE) and n-butanol (BE). Bioassay (ASTM D3345-74) guided fractionation was carried out on the basis of the least wood loss (LWL). The anti-termite activity (ATA) was in the order of EE>CE>PE>BE, LWLEE = 10.54% at 500 ppm. In contrast, controls were severely damaged. Fractions of EE showed ATA in the order of F2>F3>F1, LWLF2 = 5.53%. Chemical and spectral studies proposed that the active compounds in EE were of phenolic acids. Fraction F2 was then partitioned into aqueous and organic layers at pH ~3 and the organic residue was subjected to chromatographic separation. The chemical and biological properties of the F2 fractions were not altered and the ATA sequence was F2AII>F2AIII>(F2R≈F2AI), LWLF2AII, F2AIII = 6.86, 9.12%. Vanillic (Va) and syringic (Sa) acids were finally isolated from F2AII and F2AIII. Their structures were characterized by means of spectroscopic evidences. They acted as repellent rather than toxicant and the lowest concentration for preventing visible damage was 200 ppm (Va) and 300 ppm (Sa). Additionally, phenolic extraction (pH 6~7) and subsequent column chromatography (CC) of the extract afforded 4 fractions. The ATA of the fractions was FB>FC>FA>FD, LWLFB = 17.24%. Fraction FB was further fractionated by repeated CC to yield methyl vanillate (Mv) and syringol (Sy) from FB2 and FB3, respectively. The sequence of ATA for these potential biocides was (Mv≈Va)>Sa>Sy.
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Keywords
Bioassay Guided Isolation Of Antitermite Compounds From The Bark , Rhizophora Apiculata
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