Bioassay Directed Chemical Study of Antimalarial Substances from Clerodendrum myricoides and Dodonaea angustifolia and Comparative Chemical Studies of Moringa stenopetala and Moringa oleifera
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Date
2015-06
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Addis Ababa Universty
Abstract
Human beings have since time immemorial used plants for different purposes including as food,
for flavor, cosmetic, dying clothes, and above all as medicine for treating a wide spectrum of
diseases. The main aim of this dissertation work is to find rationale for the use of selected plants in
combating one of the most challenging diseases in the world, namely, malaria. The selection of the
plant materials for the study was based on ethnomedicinal uses. This led to the need for systematic
investigation of two plants, Clerodendrum myricoides (Lamiaceae) and Dodonaea angustifolia
(Sapindaceae), which are indigenous medicinal plants traditionally used as remedies against
malaria in some parts of Ethiopia. In the course of this study, bioassay guided investigation on the
antiplasmodial activities of the leaves of C. myricoides resulted in the isolation of two active
compounds, namely, α-spinasterol (63) and sitosterol-3-O-β-D-glucoside (64), which significantly
suppress parasitaemia by 51% and 44% at 40 mg/kg, respectively.
Furthermore, the acetone extract of the leaves of C. myricoides afforded verbascoside (12),
ixoroside (73), and compound 71. To our knowledge there is no report in the literature for
compound 71. Tetracosanoic, behenic, icosanoic, stearic, and palmitic acid were also identified
from the leaves of this plant. Investigation of the radical scavenging activities of the above
constituents resulted in verbascoside as the most active compound comparable to ascorbic acid. Bioassay guided fractionation of the ethyl acetate soluble portion of the 80% aqueous MeOH
extract of the leaves of D. angustifolia afforded three compounds, namely, pinocembrin (86),
santin (81) and 15,16-epoxy-2-hydroxy-3,13(16),14-clerodtriene-18-oic acid (128) which
exhibited high percent suppression of parasitaemia by 81% at 40 mg/kg, 80% at 50 mg/kg and
70% at 40 mg/kg, respectively. Under similar conditions chloroquine suppressed parasitaemia by
100% at 25 mg/kg. Column chromatographic fractionation of the ethyl acetate soluble portion of
the ethanol extract of D. angustifolia leaves gave three other compounds in addition to 81, 86 and
128, identified as 5,7,4’-trihydroxy-3,6-dimethoxyflavone (80), ent-16-hydroxy-labdan-3α,8β-
dihydroxy,13(14)-en-15,16-olide (114), and 5,6,7-trihydroxy-3,4’-dimethoxyflavone (125). To
our knowledge compound 125 has not been reported before as a natural product. The extracts and
the four flavonoids isolated from the leaves of D. angustifolia were tested for their antiradical
properties, which led to 5,7,4’-trihydroxy-3,6-dimethoxyflavone (80) as the most active compound.
The leaves of two Moringa species, M. stenopetala which is confined to the horn of Africa namely
Ethiopia, Somalia and Kenya and M. oleifera originally from the Indian subcontinent but now
cultivated in different parts of the world including Africa, were compared with respect to their
main chemical constituents. Different techniques including TLC, HPLC-MS, and UV-Vis
spectrophotometry were employed. Our results unambiguously showed significant differences in
the chemical profiles of the leaves of the two species. Rutin (163) is the only principal flavonoid
glycoside of the leaves of M. stenopetala, which however is not detected in the leaves of M.
oleifera. On the other hand M. oleifera contains significant amounts of two other glycosides,
namely, quercetin-3-O-β-D-glucoside (159) and kaempferol-3-O-β-D-glucoside (161). These
results are significant in distinguishing the two Moringa species. Furthermore, a simple high
performance thin layer chromatographic method was developed and validated for quantitative
analysis of rutin in the leaves of M. stenopetala. The level of rutin in the leaves of M. stenopetala
was found to be 1.9±0.08%. These fingerprinting results can be used not only to differentiate the
two species but also to establish presence or absence of adulterants, an issue that is significant in
the use and marketing of crude and derived products from Moringa leaves Further chemical investigation on the leaves of M. stenopetala afforded three compounds
identified as heptacosanol (185), sitosterol-3-O-β-D-glucoside (64), and inositol dimer (186). The
seed kernel and husk of M. stenopetala was also investigated in this study for the first time. This
resulted in the isolation and characterization of stearic acid (77), 4-(α-L-rhamnopyranosyloxy)
benzyl glucosinolate (164) and sucrose (187) from the seed kernel while the husk furnished
allantoin (191) and compound 190. To our knowledge compound 190 was not reported before as
natural product. GC-MS analysis of the fatty acids of the oil of M. stenopetala afforded oleic acid
(52%), stearic acid (9%), palmitic acid (9%), behenic acid (5%), archidic acid (5%), palmitoleic
acid (1%) and myristic acid (0.2%). The above flavonoid glycosides displayed pronounced radical
scavenging and anti-lipid peroxidation activities.
Key words: Bioassay, Clerodendrum myricoides, Dodonaea angustifolia, Sapindaceae, Lamiaceae,
Antiplasmodial, radical scavenging, pinocembrin, santin, verbascoside, Moringaceae, Fingerprint,
HPLC-MS, TLC, UV, Moringa stenopetala, Moringa oleifera, quality control, radical scavenging
Description
Keywords
Bioassay, Clerodendrum myricoides, Dodonaea angustifolia, Sapindaceae, Lamiaceae, Antiplasmodial, Radical scavenging, Pinocembrin, Santin, verbascoside, Moringaceae