| dc.description.abstract | ABSTRACT
Myrsine africana Land Maesa lanceolata Forsk are among the five medicinal
Myrsinaceae plants found in Kenya and find a wide application in ethnopharmacology as
anthelmintics and as anti-microbials. The plant parts namely; fruits, leaves, stem and root
barks were-e~acted with non polar (petroleum ether, dichloromethane, ethyl acetate and
dioxane) and polar (methanol) solvents. Chromatographic separation of these extracts on
oxalic acid impregnated silica gel (soaking in 2-3% oxalic acid solution) and active silica
gel using various solvents led to the isolation of an array of compounds whose structures
were established by physical, spectroscopic (UV, IR, IH and 13CNMR and MS) and
chemical properties. The classes of compounds isolated included flavonoids, terpeniods
and/or steriods, anthraquinones, benzoquinones with long aliphatic side chains and a long
chain aliphatic ketone.
The level of benzoquinones was found to be high in all parts of the plants examined
compared to other secondary metabolites with the highest concentration being realised in
the fruits.
Chromatographic separation of M. africana leaf extract resulted in the isolation of
four novel flavonol glycosides which were; myricetin 3-0-3",4"-diacetylrhamnoside (171),
3'-methoxyquercetin 3-0-13-D-glucoside (173), quercetin 3-0-13-D(6-0-a-L-rhamnosyl)
galactoside (183), and quercetin 3-0-13-D-(6-0-a-L-rhamnosyl) glucoside 7-0-13-D-(4-0-aL-rhamnosyl)glucoside
(184) together with known one~Kaempferol (102), quercetin (77),
myricetin (100), myricetin 3-0-rhamnoside (170), rnyricetin 7-0-rhamnoside (172),
quercetin 3-0-rhamnoside (lID, quercetin 3-0-6--D- glucoside (175), quercetin 3-0-6-Dgalactoside
(178), myricetin 3-0-6-D-galactoside (179), myricetin 3-0-xyloside (176),
myricetin 3-0-arabinoside (177), kaempferol 3-0-13-D-(6-0-a-L-rhamnosyl) glucoside
(180), 3'-O-methylquercetin 3-0-13-D-(6-0-a-rhamnosyl) glucoside (liD quercetin 3-0-13D-(6-0-a-L-rhamnosyl)
glucoside (182).
Sitosterol (105), stigmasterol (148), stigmasterol 3-0-glucoside (190), taraxerone
(187) and myricadiol (188) and spinasterol 3-0-6- D-glucoside (110) were the terpenes
and/or steroids isolated from various parts of the plant.
Four anthraquinone pigments, emodin (23), chrysophanol (25), physcion (197) and
2-hydroxychrysophanol (161), and nepodiri (162) a long with gallic acid (194) and a long
chain aliphatic ketone, 2-triacontanone (196) were also isolated from the plant.
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Apart from the compounds listed above several benzoquinones with long aliphatic
side chains were isolated, including five considered to be obtained from the plant for the
first time. These are: 2,5-dihydroxy-6-methyl-3-undecyl-l ,4-benzoquinones (muketanin)
(202), methylvilangin (82), anhydromethylvilangin (,[l), methylenebis (2,5-dihydroxy-4-
-~
tridecy 1-3,6- benzoquinones) (214) and 2,3 -dihydroxy -6- heptadecy 1-1,4-benzoquinones (206).
Together with these, other known benzoquinones isolated were 2,3-dihydroxy-6-undecy-l,4benzoquinone
(myrsinone) (129), 2-hydroxy-5-0-methyl-3-undecyl-l,4-benzoquinone (5-0methylembelin
(130)) and myrsinaquinone (136).
On the other hand a chromatographic analysis of M. lanceolata parts led t~ the
isolation of three new benzoquinones 2-hydroxy-5-methoxy-6-methyl-3-undecyl-l,4benzoquinone
(219), 2,5-dihydroxy-3-(nonadec-14'z-enyl)-1 ,4-benzoquinone (220) and the
fourteen carbon chain linked bisbenzoquinone, lanciaquinone (222). The known
benzoquinones from this plant were identified as maesaquinone (11), acetylmaesaquinone
(94), 2,5-dihydroxy-3-pentadecyl-l ,4-benzoquinone (126), 2,5-dihydroxy-3-(pentadec-1O'zenyl)-I,4-benzoquinone
(127) and 2-hydroxy-5-methoxy-3-(pentadec-1 O'z-enyl)-1 ,4benzoquinone(maesanin,
128). The other quinones isolated from this plant were emodin (23)
and chrysophanol (m. Taraxerol (193) and spinasterol 3-0-glucoside (110) were the only
terpenoids isolated and characterised from this plant.
Apart from isolation and characterisation work, structural modification of known
benzoquinones and synthesis of 2,5-dihydroxy-3-alkyl-f~-benzoquinones were attempted
. ~
...
for structure activity relationship studies for their alkyl moiety. The compounds prepared
were 2,5-dihydroxy-3-ethyl-l,4-benzoquinone (223), 2, 5 -dihydroxy-3-propyl-I,4benzoquinone
(224), 2,5-dihydroxy-3-pentyl-l,4-benzoquinone (225), 2,5-dihydroxy-3heptyl-I,4-benzoquinone
(226), 2,5-dihydroxy-3-nonyl-I,4-benzoquinone (227), 2,5dihydroxy-3-undecyl-l,4-benzoquinone
(embelin, Q2), 2,5-dihydroxy-3-tridecyl-I,4benzoquinone
(rapanone, 1Q) and 2,5-dihydroxy-3-pentadecyl-I,4-benzoquinone (126).
Biological activity tests such as insect anti-feedant, anti-microbiols, phytotoxicity,
acaricidal, contact insecticidal and nematicidal were carried out with crude extracts from
various plant parts and also with some of the compounds isolated, prepared and/or
structurally modified.
Insect anti-feedant tests were carried out with Epilachna varivestis Muls on
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Phaseolus vulgaris L using "choice" test in which one bean leaf with one half treated and
the other half untreated is in one petri dish. Dichloromethane, ethyl acetate, and methanol
extracts of both M. africana and M. lanceolata parts leaves, fruits stem and root barks in
- - ~
three concentrations (O.S, 0.2 and 0.1 %, w/v) were tested. Similarly several compounds
including the isolates, structurally modified ones as well as the prepared 2,S-dihydroxy-3alkyl-l,4-benzoquinones
in up to five concentrations (0.1, O.OS, 0.02S, 0.02 and 0.01 %
w/v) were also tested and results showed that both CH2Cl2 and ethyl acetate extracts of M.
africana various parts gave less than 5% consumption by E. varivestis at all concentrations
tested. However, extracts from M. lanceolata various parts did not deter the test animals
from feeding. In this case the percentage consumption at all concentrations was over 90%.
On the other hand several components of M. africana parts were tested at different
concentrations and the activity of related chemical structures compared. Results obtained
from the test showed that embelin (Q2) and rapanone eZID gave percent consumption as
15% and 2S% respectively when tested at 0.02%. Similarly 2,S-dihydroxy-3-nonyl-l,4benzoquinone
(227) and 2,S-dihydroxy-3-pentadecyl-l,4-benzoquinone (126) afforded
percentage consumption as 40 and SO respectively when tested at the same concentration.
Phytotoxicity effects of benzoquinones has been demonstrated by measuring the
inhibitory activity of these compounds at 1000, SOO and 2S0 ppm concentrations on
seedling growth of Radish seeds (Scorlet globe variety). Bioassays showed that radicle
elongation of seedlings tested was inhibited by most Qr the benzoquinones tested. For
example, myrsinone (129), embelin (Q2), 2,S-dihydroxy-3-.pentadecyl-l,4-benzoquinone
(126), rapanone (70), muketanin (202), 2,S-dihydroxy-3-alkyl-l,4-benzoquinones 223, 224,
22S, 226 and 227, maesaquinone ill), maesanin (128), and acetylmaesaquinone (2.1)
inhibited radicle elongation at 1000 ppm with values ranging from O-S% and percentage
germination in the range 0-30% after 72 hours.
Nematicidal activity tests of benz oquin ones using Meloidogyn incognita revealed that
at 100 ppm and 1000 ppm, the compounds, maesanin (128) and S-O-methylembelin (130)
were 82% and 80.S% nematicidal respectively. Embelin (Q2), rapanone (70), methylvilangin
(m, compounds 223, 224, 22S, 226, 227 and maesaquinone ill) gave values ranging from
52-73% with higher values recorded for embelin and rapanone. The latter compounds were
considered not active as nematicides since the recorded values were less than 80%.
Bioautographic technique for detecting fungitoxic substances on t.l.c revealed that
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at concentrations 50 ppm, 10 ppm and 1 ppm acetylmaesaquinone (.21), muketanin (202),
compound (206), 2,5-dihydroxy-3-(nonadec-14'z-enyl)-1 ,4-benzoquinone (220), embelin
(69), rapanone (70), anhydrovilangin (ru, methylvilangin (82), maesanin (128),
maesaquinone (11) and 5-0-methylembe1in (130) were active against Cladosporium
cucumerinum by displaying a white spot after incubation period.
Anti-bacterial tests were conducted using a wide range of both Gram-positive and
Gram-negative bacteria. Embelin (Q2), rapanone (1Q), 2,5-dihydroxy-3-alkyl-1,4benzoquinones
(220) and (126) displayed strong antibacterial activity against Candida
albicans and Streptococus faecacus but showed weak activity against Pseudomonas
acidororous. On the other hand the compounds (223), (224), (225), (226) and (227) showed
a weak activity against Candida and no activity against .s.. faecalus.
Results of the effect of benzoquinone derivatives investigated on Boophilus
microplus (Canestrinii) the southern cattle tick revealed that embelin (69), myrsinone (129),
maesaquinone (11) and maesanin (128) were quite effective in inhibiting the hatching of
this anthropod eggs. The order of activity in inhibiting eggs hatching at 8 ug per tick was:
embelin 95.3% > maesanin 91.0% > maesaquinone 72.2% > myrsinone 45.5%.
Finally contact toxicity effect of benzoquinone compounds on Cylas formicarius
elegantulus, a sweet potato weevil showed that at 120 mg per insect, embelin (Q2), rapanone
(1Q), embelin dimethylether (201), maesaquinone dimethylether (217) and 2,5-dihydroxy-3pentadecyl-l,4-benzoquinone
(126) brought about 100~fnii.sect mortality 48 hours after
treatment. | en |
