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.