Isolation and characterization of limonoids from swietenia macrophylla and their antioxidant and antimicrobial activities
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Date
2009
Authors
Seok Keik, Tan
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Abstract
Swietenia macrophylla King, a tree up to 30-35 m tall, is used traditionally by
local folks to cure diabetes and high-blood pressure. The leaves of this tree,
collected from the campus of Universiti Sains Malaysia, were air-dried, powdered
and extracted with n-hexane, dichloromethane and methanol. The
dichloromethane and n-hexane extracts were separated by column
chromatography and preparative thin layer chromatography on silica gel to give
seven limonoids, among which four are new limonoids, namely swietephragmins
H-J [1-3] and swietemacrophine [4]. The structures of the new compounds were
elucidated by spectroscopic methods using lD and 2D NMR, HRESIMS, UV and
IR, and were identified as phragmalin-type limonoids. Meanwhile, the known
compounds were identified as swietenine (5], swietenolide [ 6] and 3-0-tigloylswietenolide
[ 7], which are mexicanolide-type limonoids. These known
compounds were identified based on their spectroscopic data and also by
comparison with related literature.
The total phenolic, total tannin and total flavonoid contents of Swietenia
macrophylla leaf extracts were examined and the contents were decreased in the
following order: methanol extract > dichloromethane extract > n-hexane extract.
The methanol, dichloromethane and n-hexane extracts, together with
swietephragmin H [1], swietephragmin I [2] and swietenolide [6) were further
evaluated for their antioxidant activity using DPPH· radical scavenging assay. The
results showed that all of the extracts tested were active as radical scavengers,
with methanol extract, dichloromethane extract and n-hexane extract showing IC50
at 7.67 ± 0.29, 15.00 ± 0.50 and 26.00 ± 1.73 ~g/mL, respectively. For the pure
compounds tested, swietenolide [6] showed IC50 at 121.50 ± 0.87 ~g/mL, while
the ICso value for swietephramin H [J] and swietephragmin I [2], which showed
low activity, cannot be determined in this study.
The antimicrobial activity of the extracts and compounds [J]-[7] isolated from the
leaves of S. macrophylla were also evaluated against four species of bacteria and
one species of yeast. The methanol and dichloromethane extracts were active
against the Gram-positive bacteria tested, Staphylococcus aureus and Bacillus
subtilis, and were moderately or inactive against the Gram-negative bacteria tested,
Escherichia coli and Pseudomonas aeruginosa. The methanol extract also showed
antifungal properties. On the other hand, then-hexane extract and compounds [J][
7] were found inactive towards all the microorganisms tested.
Description
Keywords
Swietenia macrophylla , Antimicrobial activities