Extractive from seven African medicinal plants.
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Date
2003
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Abstract
This PhD thesis describes a phytochemical investigation of seven medicinal plants,
namely, Ledebouria ovatifolia (Hyacinthaceae), Eucomis pole-evansii
(Hyacinthaceae ), Lachenalia rub ida (Hyacinthaceae), Drimia capitata
(Hyacinthaceae ), Papaver aculeatum (Papaveraceae), Spilanthes mauritiana
(Asteraceae) and Tachiadenus longiflorus (Gentianaceae).
The southern African Hyacinthaceae is a large, chemically and morphologically
diverse group of plants. Plants of the genus Ledebouria are used extensively by
traditional healers in Kwazulu-Natal, particularly in enemas and as purgatives for both
humans and cattle. Investigations of Ledebouria ovatifolia led to the isolation of three
compounds, a novel norlignan, a class, which has never before been found in this
family, and two eucosterol-type compounds. Chemical investigations of Eucomis
pole-evansii and Lachenalia rub ida have revealed the presence of two
homoisoflavonoids of the 3-benzyl-4-chromanone type, a novel 3-benzylidene-4-
chromanone type homoisoflavonoid as well as a novel 3-benzylchromone.
Investigations of Drimia capitata have yielded a novel bufadienolide and its glycoside
Plants of the family Papaveraceae have been of great interest chemically, as they
contain alkaloids such as morphine and codeine. Morphine is an intense analgesic
used to treat chronic pain, while codeine is milder and is found in cough syrups and
headache remedies. The species Papaver aculeatum is thought to be a premature
member of the Papaveraceae and it was thought that it might contain precursors to
these alkaloids. This plant yielded an alkaloid, (+ )-N-acetylanonaine.
In South Africa, the African plant Spilanthes mauritiana (Asteraceae), is used
medicinally by the Zulus as an oral local analgesic for the relief of toothache. Other
medicinal usage of this plant includes healing broken limbs, stomach-ache, diarrhoea,
bladder complaints and headaches. This plant yielded one known and one novel
isobutylamide. The known isobutylamide, spilanthol, has been attributed with
larvicidal and other insecticidal properties.
Members of the family Gentianaceae commonly accumulate bitter substances called
iridoids. The species Tachiadenus longiflorus yielded the known triterpenoid,
oleanolic acid; two known coumarins, scopoletin and scoparone; and what appears to
be an iridoid derivative. Syntheses of aesculetin, scoparone and isoscopoletin were
also performed for comparison purposes.
The final chapter in this thesis is an attempt to synthesise the norlignan isolated from
Ledebouria ovatifolia. This procedure involves firstly the synthesis of the appropriate
chalcone, secondly the formation of the appropriate Grignard reagent and its
attachment to the chalcone, thirdly reduction of the vinyl ketone to form the vinyl
alcohol and finally dehydration to form the norlignan. This unfortunately did not
occur, however a novel cyc1isation product was formed and was identified as (E)-3-
vinyl-l-( 4 '-hydroxypheny 1)-3",4 "-dimethoxyindene.
Description
Thesis (Ph.D.)-University of Natal, Durban, 2003.
Keywords
Botanical chemistry., Plants -- Analysis., Asparagaceae., Papaveraceae., Compositae., Gentianaceae., Medicinal plants -- Africa., Theses -- Chemistry.