Antimalarials from nature

Flavones: An important scaffold for medicinal chemistry

Infections with protozoan parasites are a major cause of disease and mortality in many tropical countries of the world. Diseases caused by species of the genera Trypanosoma (Human African Trypanosomiasis and Chagas Disease) and Leishmania (various forms of Leishmaniasis) are among the seventeen "Neglected Tropical Diseases" (NTDs) defined by the WHO. Furthermore, malaria (caused by various Plasmodium species) can be considered a neglected disease in certain countries and with regard to availability and affordability of the antimalarials. Living organisms, especially plants, provide an innumerable number of molecules with potential for the treatment of many serious diseases. The current review attempts to give an overview on the potential of such plant-derived natural products as antiprotozoal leads and/or drugs in the fight against NTDs. In part I, a general description of the diseases, the current state of therapy and need for new therapeuticals, assay methods and strategies applied in the search for new plant derived natural products against these diseases and an overview on natural products of terpenoid origin with antiprotozoal potential were given. The present part II compiles the current knowledge on natural products with antiprotozoal activity that are derived from the shikimate pathway (lignans, coumarins, caffeic acid derivatives), quinones of various structural classes, compounds formed via the polyketide pathways (flavonoids and related compounds, chromenes and related benzopyrans and benzofurans, xanthones, acetogenins from Annonaceae and polyacetylenes) as well as the diverse classes of alkaloids. In total, both parts compile the literature on almost 900 different plant-derived natural products and their activity data, taken from over 800 references. These data, as the result of enormous efforts of numerous research groups world-wide, illustrate that plant secondary metabolites represent an immensely rich source of chemical diversity with an extremely high potential to yield a wealth of lead structures towards new therapies for NTDs. Only a small percentage, however, of the roughly 200,000 plant species on earth have been studied chemically and only a small percentage of these plants or their constituents has been investigated for antiprotozoal activity. The repository of plant-derived natural products hence deserves to be investigated even more intensely than it has been up to present.

The Potential of Secondary Metabolites from Plants as Drugs or Leads Against Protozoan Neglected Diseases – Part I

Antimalarial activity of 20 crude extracts from nine African medicinal plants used in Kinshasa, Congo.

Recent trends in research into African medicinal plants

A new biflavanoid, ent-naringeninyl-(I-3alpha,II-8)-4'-O-methylnaringenin (6), along with five known xanthones and two known biflavonoids, was isolated from the root bark of Garcinia livingstonei collected in Tanzania. The absolute configuration of 6 was established by CD spectroscopy. This compound showed moderate activity against P. falciparum (IC(50) 6.7 microM). Antitrypanosomal activity (IC(50) 0.87 microM) was observed for 1,4,5-trihydroxy-3-(3-methylbut-2-enyl)-9H-xanthen-9-one (3). The dimeric xanthone garcilivin A (4) showed a higher and nonselective antiparasitic activity and cytotoxicity (IC(50) 2.0 microM against MRC-5 cells) than its diastereoisomer garcilivin C (5) (IC(50) 52.3 microM).

Antiparasitic activity of some xanthones and biflavonoids from the root bark of Garcinia livingstonei.

Biological Activities of Cryptolepine, An Alkaloid from Cryptolepis sanguinolenta

Guaianolide Glucosides from Elephantopus scaber

The Isolation of a Long Chain Phenol fromSpondias mombin

Structure and Antimicrobial Activity Relationship of Doubly-Linked Procyanidins

D. Berghe

Papers

Antiparasitic activity of some xanthones and biflavonoids from the root bark of Garcinia livingstonei.

Biological Activities of Cryptolepine, An Alkaloid from Cryptolepis sanguinolenta

Guaianolide Glucosides from Elephantopus scaber

The Isolation of a Long Chain Phenol fromSpondias mombin

Structure and Antimicrobial Activity Relationship of Doubly-Linked Procyanidins