The chemical constituents of Ehretia rigida, Apodytes dimidiata and Ocotea kenyensis.
Three species have been investigated in this project: Iso-ocobullenone (p 23) and its probable precursor (p 27) have been isolated from the leaves and bark of Ocotea kenyensis. This is only the second time that these compounds have been isolated and the first time from this species. The isolation of these two compounds in the leaves establishes a commercially important chemical link with the bark. The bark of the closely related Ocotea bullata is the most sought after source of "muthi" in the Kwa-Zulu Natal region and it is becoming a very scarce commodity. The leaves of Ocotea kenyensis have also yielded related compounds including A8'-3,5-dimethoxy-3',4'-methylenedioxy-l ',2',3',4'-tetrahydro-6' -oxo-7,1',8,3'-neolignan which is described here for the first time. Other compounds isolated were bacterialprenol, triacontane, B-sitosterol and a previously undescribed isoprenoid. An investigation into the molluscicidal potential of compounds in Apodytes dimidiata was extended with a view toward control of the population of the intermediary snail host for bilharzia-causing trypanosomes. This study afforded the known compounds squalene, lupeol, betulinic acid and catechin. The synthesis of a previously isolated compound, 4-ethyl catechol, with molluscicidal activity was successfully completed and its structure and activity were confirmed. A bio-assay guided isolation procedure was used to determine the potential value of compounds in Ehretia rigida for the control of sleeping sickness. Allantoin, a- and B-amyrin, triacontanol and B-sitosterol were isolated. Activity of the extracts was not high enough to be of commercial value.