Bioassay Guided Isolation Of Antitermite Compounds From The Bark Of Rhizophora Apiculata
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Date
2009-11
Authors
Kong Nein, Hing
Journal Title
Journal ISSN
Volume Title
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.
Description
Keywords
Bioassay Guided Isolation Of Antitermite Compounds From The Bark , Rhizophora Apiculata