Extractive from seven African medicinal plants.

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.