Several isoflavones [formononetin (1), castanin (5), odoratin (6), glycitein (7), pseudobaptogenin (8), fujikinetin (9), and cuneatin (10)] were isolated from Dalbergia frutescens, and their antiprotozoal activities were determined against Giardia intestinalis. Among these compounds, formononetin (1) was the most potent antigiardial agent, with an IC(50) value of 30 ng/mL (approximately 0.1 microM), as compared to the value for metronidazole, the current drug of choice, of 100 ng/mL (approximately 0.6 microM). Three isoflavones closely related to formononetin [daidzein (2), biochanin A (3) and genistein (4)] were also evaluated, but they were at least 100 times less active than 1. Formononetin (1) may thus be an interesting lead for development of new antigiardial agents or as a probe for a new mechanistic target.

Flavonoids and their glycosides form a large group of polyphenolic compounds which are widely distributed in plants. 2,3) Animals depend on plants for flavonoids as they are unable to biosynthesize them.4) The exception was the detection of flavonoids in butterfly wings with the likely source being the plant food of the larva.5) Flavonoids add colour, 6) flavour and processing characteristics to many foods (fruits and vegetables) and drinks (tea, wine). 7) So far, over 4000 flavonoid derivatives have been identified and numerous beneficial health effects including, anti-inflammatory, [8][9][10] antiviral 11) and anti-cancer 8,12,13) properties have been reported. Some epidemiological studies have also demonstrated that the intake of flavonoids reduced the risk of cardiovascular diseases. 8,[14][15][16] Most of the pharmacological activities could be attributed to their ability to inhibit certain enzymes and to their oxygen free radical scavenging and iron chelating capabilities.17) The antioxidant properties are suggested to be due to the number and arrangement of their phenolic hydroxyl groups.18) It has been shown that 3-hydroxy-, 7-hydroxy-and 5-hydroxyflavones have hypochlorite scavenging activity with 3-hydroxyflavone showing the greatest effect.19) Depending on the concentration and the reaction conditions, flavonoids could act as antioxidants as well as prooxidants. 17)Toxicity of some flavonoids has been attributed to their prooxidant behavior. Hence, careful examination of flavonoids for their behavior in varying reaction conditions has to be carried out before being considered for therapeutic uses. 17)Although in vitro experiments have shown that flavonoids possess a wide range of biological activities, their overall function in vivo has to be clarified. It has been observed that only aglycones and flavonoid glucosides are absorbed in the small intestine.18) They are then metabolized rapidly to methylated, glucuronidated or sulphated metabolites in the jejunal and ileal parts of the small intestine. After metabolism in the intestine, the flavonoids are further metabolized in the liver to yield various conjugated forms. The reactions include methylation, sulphation and glucuronidation. Conjugation is essentially a detoxification process in which the compounds are made to eliminate by way of bile and urine by increasing their hydrophilic character.20) The unabsorbed flavonoids undergo further metabolism by the bacterial enzymes in the colon.21) Using animal models, human trials and in vitro fermentation experiments, it was shown that the intestinal microorganisms are greatly responsible for catabolism and scission of the flavonoid. Scission of the flavonoid structure depends on their hydroxylation pattern.21) Absence of hydroxyl groups in the B-ring for example, prevents ring scission. In vitro metabolism studies of flavonoids using rat liver microsomes showed that the B-ring is the main structural moiety that undergoes biotransformation. B-rings with a single hydroxyl group at C-4Ј or none at all get hy...