283
11.6 Antimalarial Agents
Many plants are used in traditional medicine for the treatment of malaria. It is therefore worthy to study such plants, which have been used over the centuries for
medicinal purposes. The newly developed techniques in the area of isolation, characterization and pharmacological testing have led to an increased interest in plants
as a source of new drugs. Several classes of the secondary plant substances are
responsible for antimalarial activity, but the most important and diverse biopotency
has been observed in alkaloids, quassinoids and sesquiterpene lactones (Saxena
et al. 2003). Quinine, an alkaloid isolated from the bark of Cinchona species
(Rubiaceae), was the first antimalarial drug. It is one of the most important antimalarial drugs that are still used today. The discovery of artemisinin, the most potent
antimalarial drug, and the success of quinine, both from plant sources, have led to
the exploration of plants as antimalarial agents. Artemisinin (qinghao su) is isolated
from the plant Artemisia annua (White 1997). Now several research groups are
working to develop new antimalarial drugs in order to combat chloroquinoneresistant malarial parasite especially Plasmodium falciparum.
Some of the active constituents isolated from the root bark of Zanthoxylum gilletii (Rutaceae), the tubers of Cyperus rotundus (Cyperaceae) and the root bark of
Margaritaria discoidea (Euphorbiaceae) were a-cyperone, N-isobutyldeca-2,4dienamide and securinine, respectively. The significant antimalarial activity of these
compounds was attributed to the presence of a,b-unsaturated carbonyl moiety. This
moiety was supposed to undergo a Michael reaction with nucleophilic sites in the
DNA molecule of the malarial parasite and inhibit the growth of P. falciparum
(Weenen et al. 1990; Achenbach et al. 1992). Several plant-based compounds can
thus be utilized for the successful treatment of malaria, which is one of the most
prevalent insect-borne diseases.
11.7 Methods of Extraction
A systematic methodology is inevitable for the scientific analysis of plant components. Active components may be present in any parts of the plant. Plants are collected either randomly or based on the knowledge from classical texts like those of
Ayurveda and traditional healers. Usually crude aqueous or alcohol extracts are
used for initial screening of the plants for antimicrobial activities, and it can be followed by different organic extraction strategies. Since most of the compounds from
plants are aromatic or saturated organic constituents, they are mostly obtained
through the initial extraction using ethanol or methanol. For taking alcoholic
extracts, the plant parts are dried, ground to fine powder and then soaked in ethanol
or methanol for extended periods. The slurry is filtered and washed, then it may be
11 Antimicrobial Agents from Plants
11.6 Antimalarial Agents
Many plants are used in traditional medicine for the treatment of malaria. It is therefore worthy to study such plants, which have been used over the centuries for
medicinal purposes. The newly developed techniques in the area of isolation, characterization and pharmacological testing have led to an increased interest in plants
as a source of new drugs. Several classes of the secondary plant substances are
responsible for antimalarial activity, but the most important and diverse biopotency
has been observed in alkaloids, quassinoids and sesquiterpene lactones (Saxena
et al. 2003). Quinine, an alkaloid isolated from the bark of Cinchona species
(Rubiaceae), was the first antimalarial drug. It is one of the most important antimalarial drugs that are still used today. The discovery of artemisinin, the most potent
antimalarial drug, and the success of quinine, both from plant sources, have led to
the exploration of plants as antimalarial agents. Artemisinin (qinghao su) is isolated
from the plant Artemisia annua (White 1997). Now several research groups are
working to develop new antimalarial drugs in order to combat chloroquinoneresistant malarial parasite especially Plasmodium falciparum.
Some of the active constituents isolated from the root bark of Zanthoxylum gilletii (Rutaceae), the tubers of Cyperus rotundus (Cyperaceae) and the root bark of
Margaritaria discoidea (Euphorbiaceae) were a-cyperone, N-isobutyldeca-2,4dienamide and securinine, respectively. The significant antimalarial activity of these
compounds was attributed to the presence of a,b-unsaturated carbonyl moiety. This
moiety was supposed to undergo a Michael reaction with nucleophilic sites in the
DNA molecule of the malarial parasite and inhibit the growth of P. falciparum
(Weenen et al. 1990; Achenbach et al. 1992). Several plant-based compounds can
thus be utilized for the successful treatment of malaria, which is one of the most
prevalent insect-borne diseases.
11.7 Methods of Extraction
A systematic methodology is inevitable for the scientific analysis of plant components. Active components may be present in any parts of the plant. Plants are collected either randomly or based on the knowledge from classical texts like those of
Ayurveda and traditional healers. Usually crude aqueous or alcohol extracts are
used for initial screening of the plants for antimicrobial activities, and it can be followed by different organic extraction strategies. Since most of the compounds from
plants are aromatic or saturated organic constituents, they are mostly obtained
through the initial extraction using ethanol or methanol. For taking alcoholic
extracts, the plant parts are dried, ground to fine powder and then soaked in ethanol
or methanol for extended periods. The slurry is filtered and washed, then it may be
11 Antimicrobial Agents from Plants