Malaria remains one of the most serious world health problem and the major cause of mortality and morbidity in the endemic regions. Brazil is among the 30 high-burden countries and most of the cases occur in the Legal Amazonian Region. New chemotherapeutical agents are needed for the treatment of malaria. Many plant species are used in traditional medicines of malarious countries and a relatively few number of these have been investigated for evaluation of their antimalarial effect. Still lower is the number of those that have had the active natural compounds isolated and the toxicity determined. This area is, then, of great research interest. A discovery project of antimalarial natural products from plants traditionally used to treat malaria must include in vitro and in vivo assays as well as bioguided isolation of active compounds. The final products would be antimalarial chemical entities, potential new drugs or templates for new drugs development, and/or standardized antimalarial extracts which are required for pre-clinical and clinical studies when the aim is the development of effective and safe phythomedicines. This review discusses these two approaches, presents briefly the screening methodologies for evaluation of antimalarial activity and focuses the activity of alkaloids belonging to different structural classes as well as its importance as new antimalarial drugs or leads and chemical markers for phytomedicines.

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Pretreatment of rats with hesperidin (50 and 100 mg kg-1, s.c.) reduced the paw oedema induced by carrageenan by 47 and 63%, respectively, within 5 h. The effect was equivalent to that produced by indomethacin (10 mg kg-1, p.o.), although unrelated to the administered dose, particularly at high doses. At 100 mg kg-1 hesperidin decreased the rat paw oedema induced by dextran by 33%, without influencing the histamine-induced paw oedema. Hesperidin also inhibited pleurisy induced by carrageenan, reducing the volume of exudate and the number of migrating leucocytes by 48 and 34%, respectively, of control values. Equal doses of duartin and claussequinone were ineffective in all the above tests. Pretreatment of mice with hesperidin (100 mg kg-1, s.c.) reduced acetic acid-induced abdominal constriction by 50%, but did not affect the tail flick response. Hyperthermia induced by yeast in rats was slightly reduced by hesperidin. No lesions of the gastric mucosae were detected in rats pretreated with hesperidin. The results indicate that hesperidin obtained from citrus cultures may present a potential therapeutical use as a mild anti-inflammatory agent, being also useful as a precursor of new flavonoids endowed with such activity.

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Aqueous infusions of Brazilian Maytenus leaves are used as beverages, foodstuffs, and phytomedicines. Previously, we isolated two new flavonoid tetrasaccharides from the infusion of Maytenus aquifolium leaves that showed antiulcer activity. In this investigation a new flavonoid tetrasaccharide, kaempferol-3-O-alpha-L-rhamnopyranosyl (1-->6)-O-[alpha-L-arabinopyranosyl (1-->3)-O-alpha-L-rhamnopyranosyl (1-->2)]-O-beta-D-galactopyranoside (3), was isolated, together with kaempferol tri- and disaccharides and quercetin trisaccharides from the aqueous infusion of Maytenus ilicifolia leaves. All structures were elucidated by ES-MS and NMR spectroscopic methods. The quantitative analysis of the flavonoid glycosides from Maytenus ilicifolia and M. aquifolium has been performed by HPLC.

This paper presents a review on kaurane diterpenes and their glycoside derivatives, covering aspects of their occurrence, biological activities and the synthesis of these natural products and their analogues. First, it shows and classifies diterpenes, in accordance with the already established structural criteria in the literature. Then, kaurane diterpenes are presented, focusing on their chemical structures, occurrence in the plant kingdom and their main, recently described, biological activities. Moreover, the most significant works, published between 1964 and November 2006, which describe the total synthesis or structural transformations of some kaurane diterpenes, including either semisynthetic and/or microbiological methodologies, are consisely reviewed. At this point, some general considerations on glycosides are introduced, and kaurane glycosides are presented and discussed on the basis of their toxic importance and occurrence in the plant kingdom, having focused on related aspects of their biological activities and the relationships between these activities and the structural factors of their molecules. Finally, the principal methods of glycosidation by enzymatic and chemical processes are both presented, and a few papers on the synthesis of kaurane glycosides are succinctly discussed. Molecules 2007, 12 456

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